Origin of the Intrinsic Fluorescence of the Green Fluorescent Protein

Multiplexed and Quantitative Imaging of Live-Cell Membrane Proteins by a Precise and Controllable DNA-Encoded Amplification Reaction

Amplifying DNA conjugated affinity ligands can improve the sensitivity and multiplicity of cell imaging and play a crucial role in comprehensively deciphering cellular heterogeneity and dynamic changes during development and disease. However, the development of one-step, controllable, and quantitative DNA amplification methods for multiplexed imaging of live-cell membrane proteins is challenging. Here, we introduce the template adhesion reaction (TAR) method for assembling amplifiable DNA sequences with different affinity ligands, such as aptamers or antibodies, for amplified and multiplexed imaging of live-cell membrane proteins with high quantitative fidelity. The precisely controllable TAR enables proportional amplification of membrane protein targets with variable abundances by modulating the concentration ratios of hairpin templates and primers, thus allowing sensitive visualization of multiple membrane proteins with enhanced signal-to-noise ratios (SNRs) without disturbing their original ratios. Using TAR, we achieved signal-enhanced imaging of six proteins on the same live-cell within 1-2 h. TAR represents an innovative and programmable molecular toolkit for multiplexed profiling of membrane proteins in live-cells.

GFP Chromophore Integrated Conjugated Microporous Polymers toward Bioinspired Photocatalytic CO2 Reduction to CO

The development of highly active, durable, and low-cost metal-free catalysts for the photocatalytic CO2 reduction reaction (CO2RR) is an efficient and environmentally friendly solution to address significant problems like global warming and high energy demand. In the present study, we have demonstrated the design and synthesis of a donor-acceptor based conjugated microporous polymer (CMP), TPA-GFP, by integrating an electron donor, tris(4-ethynylphenyl)amine (TPA), with a green fluorescent protein chromophore analogue (Z)-4-(2-hydroxy-3,5-diiodobenzylidene)-1-(4-iodophenyl)-2-methyl-1H-imidazol-5(4H)-one (o-HBDI-I3) (GFP). In comparison to nondonor 1,3,5-triethynylbenzene (TEB) based TEB-GFP CMP, photocatalytic CO2 reduction using donor-acceptor based TPA-GFP CMP displays a 3-fold increment of CO production yield with a maximum CO yield of 1666 μmol g-1 at 12 h. Further, the CO selectivity increases significantly from a mere 54% in TEB-GFP to an impressive 95% in TPA-GFP. The impressive CO2 reduction efficiency and selectivity for TPA-GFP can be attributed to the efficient light-harvesting capability and facile charge separation and migration through donor-acceptor building units of the CMP. The mechanistic aspect of the photocatalytic CO2 reduction process is explored using in situ DRIFTS and DFT calculation, and a plausible photocatalytic mechanism is proposed.

Conical Intersection Accessibility Dictates Brightness in Red Fluorescent Proteins

Red fluorescent protein (RFP) variants are highly sought after for in vivo imaging since longer wavelengths improve depth and contrast in fluorescence imaging. However, the lower energy emission wavelength usually correlates with a lower fluorescent quantum yield compared to their green emitting counterparts. To guide the rational design of bright variants, we have theoretically assessed two variants (mScarlet and mRouge) which are reported to have very different brightness. Using an α-CASSCF QM/MM framework (chromophore and all protein residues within 6 Å of it in the QM region, for a total of more than 450 QM atoms), we identify key points on the ground and first excited state potential energy surfaces. The brighter variant mScarlet has a rigid scaffold, and the chromophore stays largely planar on the ground state. The dimmer variant mRouge shows more flexibility and can accommodate a pretwisted chromophore conformation which provides easier access to conical intersections. The main difference between the variants lies in the intersection seam regions, which appear largely inaccessible in mScarlet but partially accessible in mRouge. This observation is mainly related with changes in the cavity charge distribution, the hydrogen-bonding network involving the chromophore and a key ARG/THR mutation (which changes both charge and steric hindrance).

Spectroscopy and dynamics of isolated anions: Versatile instrumentation for photodetachment and photoelectron spectroscopy

Molecular anions are appealing targets for study because, compared with their neutral and cationic counterparts, they can be probed with conventional laboratory lasers without the need for multiphoton ionization schemes, and they provide spectroscopic details on the corresponding neutral molecules. Here, we describe a section of a modular instrument designed to perform high-throughput photoelectron and photodetachment spectroscopy of gas-phase anions, with future provision for time-resolved and isomer-selective spectroscopy. The instrument framework allows for the incorporation and adaptation of several ion sources, as demonstrated here with plasma (electric) discharge sources providing variable hard to soft ion generation conditions. The generated anions are separated according to their mass-to-charge ratio through time-of-flight mass spectrometry (m/zΔm/z = 500-600) and are focused into a set of perpendicular velocity-map imaging electrodes (ΔEE≈4%), where mass-selected anions are probed using laser light and the ejected electrons are velocity-map imaged. Instrument performance is demonstrated through the acquisition of photodetachment and photoelectron spectra for CH2CN-, showing sharp resonances in the vicinity of the detachment threshold assigned to rovibrational states of a dipole-bound anion and broader lifetime-limited spectral features at photon energies well above the threshold assigned to prompt autodetachment from a temporary anion resonance. Similar measurements could be performed on any molecular anions generated in the sources.

Dynamics of Anions: From Bound to Unbound States and Everything In Between

Gas-phase anions present an ideal playground for the exploration of excited-state dynamics. They offer control in terms of the mass, extent of solvation, internal temperature, and conformation. The application of a range of ion sources has opened the field to a vast array of anionic systems whose dynamics are important in areas ranging from biology to star formation. Here, we review recent experimental developments in the field of anion photodynamics, demonstrating the detailed insight into photodynamical and electron-capture processes that can be uncovered. We consider the electronic and nuclear ultrafast dynamics of electronically bound excited states along entire reaction coordinates; electronically unbound states showing that photochemical concepts, such as chromophores and Kasha's rule, are transferable to electron-driven chemistry; and nonvalence states that straddle the interface between bound and unbound states. Finally, we consider likely developments that are sure to keep the field of anion dynamics buoyant and impactful.

Fluorescent protein chromophores modified with aromatic heterocycles for photodynamic therapy and two-photon fluorescence imaging

In this paper, three fluorescent protein chromophore analogs PFPAr (PFPP, PFPC, and PFPT) were synthesized and proved to be useful for photodynamic therapy and two-photon fluorescence imaging. By adding five- or six-membered aromatic heterocycles to the photosensitizer PFP, we obtained three fluorescent protein photosensitizers PFPAr with better performances. As a demonstration, compared with the reported photosensitizer PFP, photosensitizer PFPP exhibits larger emission wavelengths (701 nm) and achieves a slight enhancement in the efficiency of singlet oxygen (ΦΔ = 23%). Notably, PFPP can perform good two-photon fluorescence imaging with an 800 nm femtosecond laser in zebrafish. In in vitro cytotoxicity assays, PFPP shows good phototoxicity (IC50 = 4.12 μM) and acceptable dark toxicity (cell viability assay >90%). The reactive oxygen imaging experiments and AO/EB double staining assay indicate that PFPP can generate singlet oxygen to eliminate A-549 tumor cells effectively with photoexcitation of 460 nm blue light (20 mW cm-2). Furthermore, PFPP can label the lysosomes of tumor cells with high specificity for lysosomes (Pearson's correlation coefficient of 0.91). Thus, our study demonstrated that the rational introduction of aromatic heterocycles into fluorescent protein photosensitizers can effectively enhance the key parameters of photosensitivity and pave the way for further two-photon photodynamic therapy.

Chemical control of excited-state reactivity of the anionic green fluorescent protein chromophore

Controlling excited-state reactivity is a long-standing challenge in photochemistry, as a desired pathway may be inaccessible or compete with other unwanted channels. An important example is internal conversion of the anionic green fluorescent protein (GFP) chromophore where non-selective progress along two competing torsional modes (P: phenolate and I: imidazolinone) impairs and enables Z-to-E photoisomerization, respectively. Developing strategies to promote photoisomerization could drive new areas of applications of GFP-like proteins. Motivated by the charge-transfer dichotomy of the torsional modes, we explore chemical substitution on the P-ring of the chromophore as a way to control excited-state pathways and improve photoisomerization. As demonstrated by methoxylation, selective P-twisting appears difficult to achieve because the electron-donating potential effects of the substituents are counteracted by inertial effects that directly retard the motion. Conversely, these effects act in concert to promote I-twisting when introducing electron-withdrawing groups. Specifically, 2,3,5-trifluorination leads to both pathway selectivity and a more direct approach to the I-twisted intersection which, in turn, doubles the photoisomerization quantum yield. Our results suggest P-ring engineering as an effective approach to boost photoisomerization of the anionic GFP chromophore.

Excited-state dynamics and fluorescence lifetime of cryogenically cooled green fluorescent protein chromophore anions

Time-resolved action spectroscopy together with a fs-pump probe scheme is used in an electrostatic ion-storage ring to address lifetimes of specific vibrational levels in electronically excited states. Here we specifically consider the excited-state lifetime of cryogenically cooled green fluorescent protein (GFP) chromophore anions which is systematically measured across the S0-S1 spectral region (450-482 nm). A long lifetime of 5.2 ± 0.3 ns is measured at the S0-S1 band origin. When exciting higher vibrational levels in S1, the lifetime changes dramatically. It decreases by more than two orders of magnitude in a narrow energy region ∼250 cm-1 (31 meV) above the 0-0 transition. This is attributed to the opening of internal conversion over an excited-state energy barrier. The applied experimental technique provides a new way to uncover even small energy barriers, which are crucial for excited-state dynamics.

Targeting Ultrafast Spectroscopic Insights into Red Fluorescent Proteins

Red fluorescent proteins (RFPs) represent an increasingly popular class of genetically encodable bioprobes and biomarkers that can advance next-generation breakthroughs across the imaging and life sciences. Since the rational design of RFPs with improved functions or enhanced versatility requires a mechanistic understanding of their working mechanisms, while fluorescence is intrinsically an ultrafast event, a suitable toolset involving steady-state and time-resolved spectroscopic techniques has become powerful in delineating key structural features and dynamic steps which govern irreversible photoconverting or reversible photoswitching RFPs, and large Stokes shift (LSS)RFPs. The pertinent cis-trans isomerization and protonation state change of RFP chromophores in their local environments, involving key residues in protein matrices, lead to rich and complicated spectral features across multiple timescales. In particular, ultrafast excited-state proton transfer in various LSSRFPs showcases the resolving power of wavelength-tunable femtosecond stimulated Raman spectroscopy (FSRS) in mapping a photocycle with crucial knowledge about the red-emitting species. Moreover, recent progress in noncanonical RFPs with a site-specifically modified chromophore provides an appealing route for efficient engineering of redder and brighter RFPs, highly desirable for bioimaging. Such an effective feedback loop involving physical chemists, protein engineers, and biomedical microscopists will enable future successes to expand fundamental knowledge and improve human health.

Alkylated green fluorescent protein chromophores: dynamics in the gas phase and in aqueous solution

Fluorescent labelling of macromolecular samples, including using the green fluorescent protein (GFP), has revolutionised the field of bioimaging. The ongoing development of fluorescent proteins require a detailed understanding of the photophysics of the biochromophore, and how chemical derivatisation influences the excited state dynamics. Here, we investigate the photophysical properties associated with the S1 state of three alkylated derivatives of the chromophore in GFP, in the gas phase using time-resolved photoelectron imaging, and in water using femtosecond fluorescence upconversion. The gas-phase lifetimes (1.6-10 ps), which are associated with the intrinsic (environment independent) dynamics, are substantially longer than the lifetimes in water (0.06-3 ps), attributed to stabilisation of both twisted intermediate structures and conical intersection seams in the condensed phase. In the gas phase, alkylation on the 3 and 5 positions of the phenyl ring slows the dynamics due to inertial effects, while a 'pre-twist' of the methine bridge through alkylation on the 2 and 6 positions significantly shortens the excited state lifetimes. Formation of a minor, long-lived (≫ 40 ps) excited state population in the gas phase is attributed to intersystem crossing to a triplet state, accessed because of a T1/S1 degeneracy in the so-called P-trap potential energy minimum associated with torsion of the single-bond in the bridging unit connecting to the phenoxide ring. A small amount of intersystem crossing is supported through TD-DFT molecular dynamics trajectories and MS-CASPT2 calculations. No such intersystem crossing occurs in water at T = 300 K or in ethanol at T ≈ 77 K, due to a significantly altered potential energy surface and P-trap geometry.

High-Resolution Spectroscopy and Selective Photoresponse of Cryogenically Cooled Green Fluorescent Protein Chromophore Anions

By time-resolved action spectroscopy of cryogenically cooled molecular ions, we have achieved a remarkable vibrational resolution in the photoresponse of the deprotonated green fluorescent protein (GFP) chromophore, a key molecular unit in the bioimaging of living cells. We define four characteristic spectral regions of the S₀-S₁ band with competing electronic and nuclear decay channels. We determine the energy barrier toward internal conversion to be ∼250 cm^-1. This inhibits internal conversion and hence statistical fragmentation near the S₀-S₁ band origin, which is identified at 481.51 ± 0.15 nm (20768 ± 6 cm^-1). The origin is red-shifted by only 221 cm^-1 compared to that of wild-type GFP at 77 K. This, together with a striking agreement between the vibronic profiles of the protein and its chromophore, suggests their similar photophysics. In combination with theory, the data reveal the coexistence of mutually energy-borrowing mechanisms between nuclei and electrons mediated by specific vibrational modes.

In Vivo Fluorescence Imaging-Guided Development of Near-Infrared AIEgens

In vivo fluorescence imaging has received extensive attention due to its distinguished advantages of excellent biosafety, high sensitivity, dual temporal-spatial resolution, real-time monitoring ability, and non-invasiveness. Aggregation-induced emission luminogens (AIEgens) with near-infrared (NIR) absorption and emission wavelengths are ideal candidate for in vivo fluorescence imaging for their large Stokes shift, high brightness and superior photostability. NIR emissive AIEgens provide deep tissue penetration depth as well as low interference from tissue autofluorescence. Here in this review, we summarize the molecular engineering strategies for constructing NIR AIEgens with high performances, including extending π-conjugation system and strengthen donor (D)-acceptor (A) interactions. Then the encapsulation strategies for increasing water solubility and biocompatibility of these NIR AIEgens are highlighted. Finally, the challenges and prospect of fabricating NIR AIEgens for in vivo fluorescence imaging are also discussed. We hope this review would provide some guidelines for further exploration of new NIR AIEgens.

Cryogenic Fluorescence Spectroscopy of Ionic Fluorones in Gaseous and Condensed Phases: New Light on Their Intrinsic Photophysics

Fluorescence spectroscopy of gas-phase ions generated through electrospray ionization is an emerging technique able to probe intrinsic molecular photophysics directly without perturbations from solvent interactions. While there is ample scope for the ongoing development of gas-phase fluorescence techniques, the recent expansion into low-temperature operating conditions accesses a wealth of data on intrinsic fluorophore photophysics, offering enhanced spectral resolution compared with room-temperature measurements, without matrix effects hindering the excited-state dynamics. This perspective reviews current progress on understanding the photophysics of anionic fluorone dyes, which exhibit an unusually large Stokes shift in the gas phase, and discusses how comparison of gas- and condensed-phase fluorescence spectra can fingerprint structural dynamics. The capacity for temperature-dependent measurements of both fluorescence emission and excitation spectra helps establish the foundation for the use of fluorone dyes as fluorescent tags in macromolecular structure determination. We suggest ideas for technique development.

Laser-Induced Fluorescence (LIF) Spectroscopy of Trapped Molecular Ions in the Gas Phase

This review focuses on the laser-induced fluorescence (LIF) spectroscopy of trapped gas-phase molecular ions, a developing field of research. Following a brief description of the theory and experimental approaches employed in general for fluorescence spectroscopy, the review summarizes the current state-of-the-art intrinsic fluorescence measurement techniques employed for gas-phase ions. Whereas the LIF spectroscopy of condensed matter systems is a well-developed area of research, the instrumentation used for such studies is not directly applicable to gas-phase ions. However, some measurement schemes employed in condensed-phase experiments could be highly beneficial for gas-phase investigations. We have included a brief discussion on some of these techniques as well. Quadrupole ion traps are commonly used for spatial confinement of ions in the ion-trap-based LIF. One of the main challenges involved in such experiments is the poor signal-to-noise ratio (SNR) arising due to weak gas-phase fluorescence emission, high background noise, and small solid angle for the fluorescence collection optics. The experimental approaches based on the integrated high-finesse optical cavities employed for the condensed-phase measurements provide a better (typically an order of magnitude more) SNR in the detected fluorescence than the single-pass detection schemes. Another key to improving the SNR is to exploit the maximum solid angle of light collection by choosing high numerical aperture (NA) collection optics. A combination of these two approaches integrated with ion traps could transmogrify this field, allowing one to study even weak fluorescence emission from gas-phase molecular ions. The review concludes by discussing the scope of the advances in the LIF instrumentation for detailed spectral characterization of fluorophores of weak gas-phase fluorescence emission, considering fluorescein as one example.

Observation of Cation Chromophore Photoisomerization of a Fluorescent Protein Using Millisecond Synchrotron Serial Crystallography and Infrared Vibrational and Visible Spectroscopy

The chromophores of reversibly switchable fluorescent proteins (rsFPs) undergo photoisomerization of both the trans and cis forms. Concurrent with cis/trans photoisomerisation, rsFPs typically become protonated on the phenolic oxygen resulting in a blue shift of the absorption. A synthetic rsFP referred to as rsEospa, derived from EosFP family, displays the same spectroscopic behavior as the GFP-like rsFP Dronpa at pH 8.4 and involves the photoconversion between nonfluorescent neutral and fluorescent anionic chromophore states. Millisecond time-resolved synchrotron serial crystallography of rsEospa at pH 8.4 shows that photoisomerization is accompanied by rearrangements of the same three residues as seen in Dronpa. However, at pH 5.5 we observe that the OFF state is identified as the cationic chromophore with additional protonation of the imidazolinone nitrogen which is concurrent with a newly formed hydrogen bond with the Glu212 carboxylate side chain. FTIR spectroscopy resolves the characteristic up-shifted carbonyl stretching frequency at 1713 cm^-1 for the cationic species. Electronic spectroscopy furthermore distinguishes the cationic absorption band at 397 nm from the neutral species at pH 8.4 seen at 387 nm. The observation of photoisomerization of the cationic chromophore state demonstrates the conical intersection for the electronic configuration, where previously fluorescence was proposed to be the main decay route for states containing imidazolinone nitrogen protonation. We present the full time-resolved room-temperature X-ray crystallographic, FTIR, and UV/vis assignment and photoconversion modeling of rsEospa.

Action-Absorption Spectroscopy at the Band Origin of the Deprotonated Green Fluorescent Protein Chromophore In Vacuo

The application of action spectroscopy in connection with determination of the S₀ to S₁ band origin in the GFP anion model chromophore (deprotonated HBDI) is discussed. We specifically address the consequences of the lowest vibrational levels in S₁ being located behind a potential-energy barrier that inhibits internal conversion to the S₀ electronic ground state. Action spectroscopy based on consecutive absorption of two photons together with internal conversion will as a consequence reveal an apparent band origin that is significantly blue-shifted.

Liquid-microjet photoelectron spectroscopy of the green fluorescent protein chromophore

Green fluorescent protein (GFP), the most widely used fluorescent protein for in vivo monitoring of biological processes, is known to undergo photooxidation reactions. However, the most fundamental property underpinning photooxidation, the electron detachment energy, has only been measured for the deprotonated GFP chromophore in the gas phase. Here, we use multiphoton ultraviolet photoelectron spectroscopy in a liquid-microjet and high-level quantum chemistry calculations to determine the electron detachment energy of the GFP chromophore in aqueous solution. The aqueous environment is found to raise the detachment energy by around 4 eV compared to the gas phase, similar to calculations of the chromophore in its native protein environment. In most cases, electron detachment is found to occur resonantly through electronically excited states of the chromophore, highlighting their importance in photo-induced electron transfer processes in the condensed phase. Our results suggest that the photooxidation properties of the GFP chromophore in an aqueous environment will be similar to those in the protein.

The electronic structures of photoactive proteins underlie many natural photoinduced processes. The authors, using UV liquid-microjet photoelectron spectroscopy and quantum chemistry calculations, determine electron detachment energies of the green fluorescent protein chromophore in aqueous solution, approaching conditions of the protein environment.

Light Driven Ultrafast Bioinspired Molecular Motors: Steering and Accelerating Photoisomerization Dynamics of Retinal

Photoisomerization of retinal protonated Schiff base in microbial and animal rhodopsins are strikingly ultrafast and highly specific. Both protein environments provide conditions for fine-tuning the photochemistry of their chromophores. Here, by combining time-resolved action absorption spectroscopy and high-level electronic structure theory, we show that similar control can be gained in a synthetically engineered retinal chromophore. By locking the dimethylated retinal Schiff base at the C11═C12 double bond in its trans configuration (L-RSB), the excited-state decay is rendered from a slow picosecond to an ultrafast subpicosecond regime in the gas phase. Steric hindrance and pretwisting of L-RSB are found to be important for a significant reduction in the excited-state energy barriers, where isomerization of the locked chromophore proceeds along C9═C10 rather than the preferred C11═C12 isomerization path. Remarkably, the accelerated excited-state dynamics also becomes steered. We show that L-RSB is capable of unidirectional 360° rotation from all-trans to 9-cis and from 9-cis to all-trans in only two distinct steps induced by consecutive absorption of two 600 nm photons. This opens a way for the rational design of red-light-driven ultrafast molecular rotary motors based on locked retinal chromophores.

Internal conversion of the anionic GFP chromophore: in and out of the I-twisted S1/S0 conical intersection seam

The functional diversity of the green fluorescent protein (GFP) family is intimately connected to the interplay between competing photo-induced transformations of the chromophore motif, anionic p-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI^-). Its ability to undergo Z/E-isomerization is of particular importance for super-resolution microscopy and emerging opportunities in optogenetics. Yet, key dynamical features of the underlying internal conversion process in the native HBDI^- chromophore remain largely elusive. We investigate the intrinsic excited-state behavior of isolated HBDI^- to resolve competing decay pathways and map out the factors governing efficiency and the stereochemical outcome of photoisomerization. Based on non-adiabatic dynamics simulations, we demonstrate that non-selective progress along the two bridge-torsional (i.e., phenolate, P, or imidazolinone, I) pathways accounts for the three decay constants reported experimentally, leading to competing ultrafast relaxation primarily along the I-twisted pathway and S₁ trapping along the P-torsion. The majority of the population (∼70%) is transferred to S₀ in the vicinity of two approximately enantiomeric minima on the I-twisted intersection seam (MECI-Is). Despite their sloped, reactant-biased topographies (suggesting low photoproduct yields), we find that decay through these intersections leads to products with a surprisingly high quantum yield of ∼30%. This demonstrates that E-isomer generation results at least in part from direct isomerization on the excited state. A photoisomerization committor analysis reveals a difference in intrinsic photoreactivity of the two MECI-Is and that the observed photoisomerization is the combined result of two effects: early, non-statistical dynamics around the less reactive intersection followed by later, near-statistical behavior around the more reactive MECI-I. Our work offers new insight into internal conversion of HBDI^- that both establishes the intrinsic properties of the chromophore and enlightens principles for the design of chromophore derivatives and protein variants with improved photoswitching properties.

Laser Photodissocation, Action Spectroscopy and Mass Spectrometry Unite to Detect and Separate Isomers

The separation and detection of isomers remains a challenge for many areas of mass spectrometry. This article highlights laser photodissociation and ion mobility strategies that have been deployed to tackle...

Fluorescence Modulation by Ultrafast Chromophore Twisting Events: Developing a Powerful Toolset for Fluorescent-Protein-Based Imaging

The advancement of modern life sciences has benefited tremendously from the discovery and development of fluorescent proteins (FPs), widely expressed in live cells to track a myriad of cellular events. The chromophores of various FPs can undergo many ultrafast photophysical and/or photochemical processes in the electronic excited state and emit fluorescence with different colors. However, the chromophore becomes essentially nonfluorescent in solution environment due to its intrinsic twisting capability upon photoexcitation. To study "microscopic" torsional events and their effects on "macroscopic" fluorescence, we have developed an integrated ultrafast characterization platform involving femtosecond transient absorption (fs-TA) and wavelength-tunable femtosecond stimulated Raman spectroscopy (FSRS). A wide range of naturally occurring, circularly permuted, non-canonical amino-acid-decorated FPs and FP-based optical highlighters with photochromicity, photoconversion, and/or photoswitching capabilities have been recently investigated in great detail. Twisting conformational motions were elucidated to exist in all of these systems but to various extents. The associated different ultrafast pathways can be monitored via frequency changes of characteristic Raman bands during primary events and functional processes. The mapped electronic and structural dynamics information is crucial and has shown great potential and initial success for the rational design of proteins and other photoreceptors with novel functions and fluorescence properties.

Tuning fast excited-state decay by ligand attachment in isolated chlorophyll a

Excited-state dynamics plays a key role for light harvesting and energy transport in photosynthetic proteins but it is nontrivial to separate the intrinsic photophysics of the light-absorbers (chlorophylls) from interactions with the protein matrix. Here we study chlorophyll a (4-coordinate complex) and axially ligated chlorophyll a (5-coordinate complex) isolated in vacuo applying mass spectrometry to shed light on the intrinsic dynamics in the absence of nearby chlorophylls, carotenoids, amino acids, and water molecules. The 4-coordinate complexes are tagged by quaternary ammonium ions while the charge is provided by a formate ligand in the case of 5-coordinate complexes. Regardless of excitation to the Soret band or the Q band, a fast ps decay is observed, which is ascribed to the decay of the lowest excited singlet state either by intersystem crossing (ISC) to nearby triplet states or by excited-state relaxation on the excited-state potential-energy surface. The lifetime of the first excited state is 15 ps with Mg²⁺ at the chlorophyll center, but only 1.7 ps when formate is attached to Mg²⁺. When the Soret band is excited, an initial sup-ps relaxation is observed which is ascribed to fast internal conversion to the first excited state. With respect to ISC, two factors seem to play a role for the reduced lifetime of the formate-chlorophyll complex: (i) The Mg ion is pulled out of the porphyrin plane thus reducing the symmetry of the chromophore, and (ii) the first excited state (Q band) and T₃ are tuned almost into resonance by the ligand, which increases the singlet-triplet mixing.

Designing Red-Shifted Molecular Emitters Based on the Annulated Locked GFP Chromophore Derivatives

Bioimaging techniques require development of a wide variety of fluorescent probes that absorb and emit red light. One way to shift absorption and emission of a chromophore to longer wavelengths is to modify its chemical structure by adding polycyclic aromatic hydrocarbon (PAH) fragments, thus increasing the conjugation length of a molecule while maintaining its rigidity. Here, we consider four novel classes of conformationally locked Green Fluorescent Protein (GFP) chromophore derivatives obtained by extending their aromatic systems in different directions. Using high-level ab initio quantum chemistry calculations, we show that the alteration of their electronic structure upon annulation may unexpectedly result in a drastic change of their fluorescent properties. A flip of optically bright and dark electronic states is most prominent in the symmetric fluorene-based derivative. The presence of a completely dark lowest-lying excited state is supported by the experimentally measured extremely low fluorescence quantum yield of the newly synthesized compound. Importantly, one of the asymmetric modes of annulation provides a very promising strategy for developing red-shifted molecular emitters with an absorption wavelength of ∼600 nm, having no significant impact on the character of the bright S-S1 transition.

Spectroscopy and photoisomerization of protonated Schiff-base retinal derivatives in vacuo

The protonated Schiff-base retinal acts as the chromophore in bacteriorhodopsin as well as in rhodopsin. In both cases, photoexcitation initializes fast isomerization which eventually results in storage of chemical energy or signaling. The details of the photophysics for this important chromophore is still not fully understood. In this study, action-absorption spectra and photoisomerization dynamics of three retinal derivatives are measured in the gas phase and compared to that of the protonated Schiff-base retinal. The retinal derivatives include C₉C₁₀trans-locked, C₁₃C₁₄trans-locked and a retinal derivative without the β-ionone ring. The spectroscopy as well as the isomerization speed of the chromophores are altered significantly as a consequence of the steric constraints.

Excited-State Dynamics of a meta-Dimethylamino Locked GFP Chromophore as a Fluorescence Turn-on Water Sensor†

Strategic incorporation of a meta-dimethylamino (-NMe₂ ) group on the conformationally locked green fluorescent protein (GFP) model chromophore (m-NMe₂ -LpHBDI) has drastically altered molecular electronic properties, counterintuitively enhancing fluorescence of only the neutral and cationic chromophores in aqueous solution. A ˜200-fold decrease in fluorescence quantum yield of m-NMe₂ -LpHBDI in alcohols (e.g., MeOH, EtOH and 2-PrOH) supports this GFP-derived compound as a fluorescence turn-on water sensor, with large fluorescence intensity differences between H₂ O and ROH emissions in various H₂ O/ROH binary mixtures. A combination of steady-state electronic spectroscopy, femtosecond transient absorption, ground-state femtosecond stimulated Raman spectroscopy (FSRS) and quantum calculations elucidates an intermolecular hydrogen-bonding chain between a solvent -OH group and the chromophore phenolic ring -NMe₂ and -OH functional groups, wherein fluorescence differences arise from an extended hydrogen-bonding network beyond the first solvation shell, as opposed to fluorescence quenching via a dark twisted intramolecular charge-transfer state. The absence of a meta-NMe₂ group twisting coordinate upon electronic excitation was corroborated by experiments on control samples without the meta-NMe₂ group or with both meta-NMe₂ and para-OH groups locked in a six-membered ring. These deep mechanistic insights stemming from GFP chromophore scaffold will enable rational design of organic, compact and environmentally friendly water sensors.

Action spectroscopy of the isolated red Kaede fluorescent protein chromophore

Incorporation of fluorescent proteins into biochemical systems has revolutionized the field of bioimaging. In a bottom-up approach, understanding the photophysics of fluorescent proteins requires detailed investigations of the light-absorbing chromophore, which can be achieved by studying the chromophore in isolation. This paper reports a photodissociation action spectroscopy study on the deprotonated anion of the red Kaede fluorescent protein chromophore, demonstrating that at least three isomers-assigned to deprotomers-are generated in the gas phase. Deprotomer-selected action spectra are recorded over the S1 ← S0 band using an instrument with differential mobility spectrometry coupled with photodissociation spectroscopy. The spectrum for the principal phenoxide deprotomer spans the 480-660 nm range with a maximum response at ≈610 nm. The imidazolate deprotomer has a blue-shifted action spectrum with a maximum response at ≈545 nm. The action spectra are consistent with excited state coupled-cluster calculations of excitation wavelengths for the deprotomers. A third gas-phase species with a distinct action spectrum is tentatively assigned to an imidazole tautomer of the principal phenoxide deprotomer. This study highlights the need for isomer-selective methods when studying the photophysics of biochromophores possessing several deprotonation sites.

A photoelectron imaging study of the deprotonated GFP chromophore anion and RNA fluorescent tags

Green fluorescent protein (GFP), together with its family of variants, is the most widely used fluorescent protein for in vivo imaging. Numerous spectroscopic studies of the isolated GFP chromophore have been aimed at understanding the electronic properties of GFP. Here, we build on earlier work [A. V. Bochenkova, C. Mooney, M. A. Parkes, J. Woodhouse, L. Zhang, R. Lewin, J. M. Ward, H. Hailes, L. H. Andersen and H. H. Fielding, Chem. Sci., 2017, 8, 3154] investigating the impact of fluorine and methoxy substituents that have been employed to tune the electronic structure of the GFP chromophore for use as fluorescent RNA tags. We present photoelectron spectra following photoexcitation over a broad range of wavelengths (364-230 nm) together with photoelectron angular distributions following photoexcitation at 364 nm, which are interpreted with the aid of quantum chemistry calculations. The results support the earlier high-level quantum chemistry calculations that predicted how fluorine and methoxy substituents tune the electronic structure and we find evidence to suggest that the methoxy substituents enhance internal conversion, most likely from the 2ππ* state which has predominantly Feshbach resonance character, to the 1ππ* state.

Excitation ratiometric chloride sensing in a standalone yellow fluorescent protein is powered by the interplay between proton transfer and conformational reorganization

Natural and laboratory-guided evolution has created a rich diversity of fluorescent protein (FP)-based sensors for chloride (Cl⁻). To date, such sensors have been limited to the Aequorea victoria green fluorescent protein (avGFP) family, and fusions with other FPs have unlocked ratiometric imaging applications. Recently, we identified the yellow fluorescent protein from jellyfish Phialidium sp. (phiYFP) as a fluorescent turn-on, self-ratiometric Cl⁻ sensor. To elucidate its working mechanism as a rare example of a single FP with this capability, we tracked the excited-state dynamics of phiYFP using femtosecond transient absorption (fs-TA) spectroscopy and target analysis. The photoexcited neutral chromophore undergoes bifurcated pathways with the twisting-motion-induced nonradiative decay and barrierless excited-state proton transfer. The latter pathway yields a weakly fluorescent anionic intermediate , followed by the formation of a red-shifted fluorescent state that enables the ratiometric response on the tens of picoseconds timescale. The redshift results from the optimized π–π stacking between chromophore Y66 and nearby Y203, an ultrafast molecular event. The anion binding leads to an increase of the chromophore pK_a and ESPT population, and the hindrance of conversion. The interplay between these two effects determines the turn-on fluorescence response to halides such as Cl⁻ but turn-off response to other anions such as nitrate as governed by different binding affinities. These deep mechanistic insights lay the foundation for guiding the targeted engineering of phiYFP and its derivatives for ratiometric imaging of cellular chloride with high selectivity.

We discovered an interplay between proton transfer and conformational reorganization that powers a standalone fluorescent-protein-based excitation-ratiometric biosensor for chloride imaging.

Resolving the ultrafast dynamics of the anionic green fluorescent protein chromophore in water

The chromophore of the green fluorescent protein (GFP) is critical for probing environmental influences on fluorescent protein behavior. Using the aqueous system as a bridge between the unconfined vacuum system and a constricting protein scaffold, we investigate the steric and electronic effects of the environment on the photodynamical behavior of the chromophore. Specifically, we apply ab initio multiple spawning to simulate five picoseconds of nonadiabatic dynamics after photoexcitation, resolving the excited-state pathways responsible for internal conversion in the aqueous chromophore. We identify an ultrafast pathway that proceeds through a short-lived (sub-picosecond) imidazolinone-twisted (I-twisted) species and a slower (several picoseconds) channel that proceeds through a long-lived phenolate-twisted (P-twisted) intermediate. The molecule navigates the non-equilibrium energy landscape via an aborted hula-twist-like motion toward the one-bond-flip dominated conical intersection seams, as opposed to following the pure one-bond-flip paths proposed by the excited-state equilibrium picture. We interpret our simulations in the context of time-resolved fluorescence experiments, which use short- and long-time components to describe the fluorescence decay of the aqueous GFP chromophore. Our results suggest that the longer time component is caused by an energetically uphill approach to the P-twisted intersection seam rather than an excited-state barrier to reach the twisted intramolecular charge-transfer species. Irrespective of the location of the nonadiabatic population events, the twisted intersection seams are inefficient at facilitating isomerization in aqueous solution. The disordered and homogeneous nature of the aqueous solvent environment facilitates non-selective stabilization with respect to I- and P-twisted species, offering an important foundation for understanding the consequences of selective stabilization in heterogeneous and rigid protein environments.

Shedding light on ultrafast ring-twisting pathways of halogenated GFP chromophores from the excited to ground state

Since green fluorescent protein (GFP) has revolutionized molecular and cellular biology for about three decades, there has been a keen interest in understanding, designing, and controlling the fluorescence properties of GFP chromophore (i.e., HBDI) derivatives from the protein matrix to solution. Amongst these cross-disciplinary efforts, the elucidation of excited-state dynamics of HBDI derivatives holds the key to correlating the light-induced processes and fluorescence quantum yield (FQY). Herein, we implement steady-state electronic spectroscopy, femtosecond transient absorption (fs-TA), femtosecond stimulated Raman spectroscopy (FSRS), and quantum calculations to study a series of mono- and dihalogenated HBDI derivatives (X = F, Cl, Br, 2F, 2Cl, and 2Br) in basic aqueous solution, gaining new insights into the photophysical reaction coordinates. In the excited state, the halogenated "floppy" chromophores exhibit an anti-heavy atom effect, reflected by strong correlations between FQY vs. Franck-Condon energy (EFC) or Stokes shift, and knrvs. EFC, as well as a swift bifurcation into the I-ring (major) and P-ring (minor) twisting motions. In the ground state, both ring-twisting motions become more susceptible to sterics and exhibit spectral signatures from the halogen-dependent hot ground-state absorption band decay in TA data. We envision this type of systematic analysis of the halogenated HBDI derivatives to provide guiding principles for the site-specific modification of GFP chromophores, and expand design space for brighter and potentially photoswitchable organic chemical probes in aqueous solution with discernible spectral signatures throughout the photocycle.

Developing Bright Green Fluorescent Protein (GFP)-like Fluorogens for Live-Cell Imaging with Nonpolar Protein-Chromophore Interactions

Fluorescence-activating proteins (FAPs) that bind a chromophore and activate its fluorescence have gained popularity in bioimaging. The fluorescence-activating and absorption-shifting tag (FAST) is a light-weight FAP that enables fast reversible fluorogen binding, thus advancing multiplex and super-resolution imaging. However, the rational design of FAST-specific fluorogens with large fluorescence enhancement (FE) remains challenging. Herein, a new fluorogen directly engineered from green fluorescent protein (GFP) chromophore by a unique double-donor-one-acceptor strategy, which exhibits an over 550-fold FE upon FAST binding and a high extinction coefficient of approximately 100,000 M^-1  cm^-1 , is reported. Correlation analysis of the excited state nonradiative decay rates and environmental factors reveal that the large FE is caused by nonpolar protein-fluorogen interactions. Our deep insights into structure-function relationships could guide the rational design of bright fluorogens for live-cell imaging with extended spectral properties such as redder emissions.

Controlling Light-Induced Proton Transfer from the GFP Chromophore

Green Fluorescent Protein (GFP) is known to undergo excited-state proton transfer (ESPT). Formation of a short H-bond favors ultrafast ESPT in GFP-like proteins, such as the GFP S65T/H148D mutant, but the detailed mechanism and its quantum nature remain to be resolved. Here we study in vacuo, light-induced proton transfer from the GFP chromophore in hydrogen-bonded complexes with two anionic proton acceptors, I^- and deprotonated trichloroacetic acid (TCA^- ). We address the role of the strong H-bond and the quantum mechanical proton-density distribution in the excited state, which determines the proton-transfer probability. Our study shows that chemical modifications to the molecular network drastically change the proton-transfer probability and it can become strongly wavelength dependent. The proton-transfer branching ratio is found to be 60 % for the TCA complex and 10 % for the iodide complex, being highly dependent on the photon energy in the latter case. Using high-level ab initio calculations, we show that light-induced proton transfer takes place in S₁ , revealing intrinsic photoacid properties of the isolated GFP chromophore in strongly bound H-bonded complexes. ESPT is found to be very sensitive to the topography of the highly anharmonic potential in S₁ , depending on the quantum-density distribution upon vibrational excitation. We also show that the S₁ potential-energy surface, and hence excited-state proton transfer, can be controlled by altering the chromophore microenvironment.

Green Fluorescent Protein GFP-Chromophore-Based Probe for the Detection of Mitochondrial Viscosity in Living Cells

Viscosity is a pivotal factor for indicating the dysfunction of the mitochondria. To date, most of the fluorescent probes developed for mitochondrial viscosity have been designed using BODIPY, hemicyanine, or pyridine-based molecular rotors as part of the core structure. Our aim with this research was to extend the range of suitable fluorophores available for the construction of such fluorescent molecular rotors for evaluating the viscosity of mitocondria. Herein, we have developed a green fluorescent protein (GFP)-chromophore-based fluorescent probe (MIT-V) for the detection of mitochondrial viscosity in live cells. MIT-V exhibited a high sensitivity toward viscosity (from 7.9 cP to 438.4 cP). The "off-on" sensing mechanism of MIT-V was ascribed to the restricted rotation of single bonds and excited-state C═C double bonds of MIT-V. Cell studies indicated that MIT-V targets the mitochondria and that it was able to monitor real-time changes in the viscosity of live HeLa cell mitochondria. Therefore, we propose that MIT-V can be used as an effective chemosensor for the real-time imaging of mitochondrial viscosity in live cells. Our results clearly demonstrate the utility of such GFP-chromophore-based derivatives for the development of viscosity-sensitive systems.

Switching between Ultrafast Pathways Enables a Green-Red Emission Ratiometric Fluorescent-Protein-Based Ca2+ Biosensor

Ratiometric indicators with long emission wavelengths are highly preferred in modern bioimaging and life sciences. Herein, we elucidated the working mechanism of a standalone red fluorescent protein (FP)-based Ca2+ biosensor, REX-GECO1, using a series of spectroscopic and computational methods. Upon 480 nm photoexcitation, the Ca2+-free biosensor chromophore becomes trapped in an excited dark state. Binding with Ca2+ switches the route to ultrafast excited-state proton transfer through a short hydrogen bond to an adjacent Glu80 residue, which is key for the biosensor's functionality. Inspired by the 2D-fluorescence map, REX-GECO1 for Ca2+ imaging in the ionomycin-treated human HeLa cells was achieved for the first time with a red/green emission ratio change (ΔR/R0) of ~300%, outperforming many FRET- and single FP-based indicators. These spectroscopy-driven discoveries enable targeted design for the next-generation biosensors with larger dynamic range and longer emission wavelengths.

Covalent Attachment of Active Enzymes to Upconversion Phosphors Allows Ratiometric Detection of Substrates

Upconverting phosphors (UCPs) convert multiple low energy photons into higher energy emission via the process of photon upconversion and offer an attractive alternative to organic fluorophores for use as luminescent probes. Here, UCPs were capped with functionalized silica in order to provide a surface to covalently conjugate proteins with surface-accessible cysteines. Variants of green fluorescent protein (GFP) and the flavoenzyme pentaerythritol tetranitrate reductase (PETNR) were then attached via maleimide-thiol coupling in order to allow energy transfer from the UCP to the GFP or flavin cofactor of PETNR, respectively. PETNR retains its activity when coupled to the UCPs, which allows reversible detection of enzyme substrates via ratiometric sensing of the enzyme redox state.

Aggregate Science: From Structures to Properties

Molecular science entails the study of structures and properties of materials at the level of single molecules or small interacting complexes of molecules. Moving beyond single molecules and well-defined complexes, aggregates (i.e., irregular clusters of many molecules) serve as a particularly useful form of materials that often display modified or wholly new properties compared to their molecular components. Some unique structures and phenomena such as polymorphic aggregates, aggregation-induced symmetry breaking, and cluster excitons are only identified in aggregates, as a few examples of their exotic features. Here, by virtue of the flourishing research on aggregation-induced emission, the concept of "aggregate science" is put forward to fill the gaps between molecules and aggregates. Structures and properties on the aggregate scale are also systematically summarized. The structure-property relationships established for aggregates are expected to contribute to new materials and technological development. Ultimately, aggregate science may become an interdisciplinary research field and serves as a general platform for academic research.

Dissecting Optical Response and Molecular Structure of Fluorescent Proteins With Non-canonical Chromophores

Tracking the structural dynamics of fluorescent protein chromophores holds the key to unlocking the fluorescence mechanisms in real time and enabling rational design principles of these powerful and versatile bioimaging probes. By combining recent chemical biology and ultrafast spectroscopy advances, we prepared the superfolder green fluorescent protein (sfGFP) and its non-canonical amino acid (ncAA) derivatives with a single chlorine, bromine, and nitro substituent at the ortho site to the phenolate oxygen of the embedded chromophore, and characterized them using an integrated toolset of femtosecond transient absorption and tunable femtosecond stimulated Raman spectroscopy (FSRS), aided by quantum calculations of the vibrational normal modes. A dominant vibrational cooling time constant of ~4 and 11 ps is revealed in Cl-GFP and Br-GFP, respectively, facilitating a ~30 and 12% increase of the fluorescent quantum yield vs. the parent sfGFP. Similar time constants were also retrieved from the transient absorption spectra, substantiating the correlated electronic and vibrational motions on the intrinsic molecular timescales. Key carbon-halogen stretching motions coupled with phenolate ring motions of the deprotonated chromophores at ca. 908 and 890 cm-1 in Cl-GFP and Br-GFP exhibit enhanced activities in the electronic excited state and blue-shift during a distinct vibrational cooling process on the ps timescale. The retrieved structural dynamics change due to targeted site-specific halogenation of the chromophore thus provides an effective means to design new GFP derivatives and enrich the bioimaging probe toolset for life and medical sciences.

Unraveling the Effect on Luminescent Properties by Postsynthetic Covalent and Noncovalent Grafting of gfp Chromophore Analogues in Nanoscale MOF-808

Here, we demonstrate mimicking of photophysical properties of native green fluorescent protein (gfp) by immobilizing the gfp chromophore analogues in nanoscale MOF-808 and further exploring the bioimaging applications. The two virtually nonfluorescent gfp chromophore analogues carrying different functionalities, BDI-AE (COOH/COOMe) and BDI-EE (COOMe/COOMe) were immobilized in nanosized MOF-808 via postsynthetic modification. An ¹H NMR and IR study confirms that BDI-AE was coordinated in NMOF-808, whereas BDI-EE was just noncovalently encapsulated. Interestingly, the extremely weakly fluorescent monomers BDI-AE and BDI-EE (QY = 0.01-0.03%, lifetime = 0.01-0.03 ns) showed a 10²-fold increase in quantum efficiency with a significantly longer excited-state lifetime (QY = 1.8-5.6%, lifetime 0.89-1.49 ns) after immobilization in the NMOF-808 scaffold. Moreover, BDI-AE@MOF-808 has 4 times higher quantum efficiency as well as longer excited-state lifetime in comparison to BDI-EE@NMOF-808 due to the rigidity imposed in the chromophore upon coordination with Zr⁴⁺ in the former case. Further, a cell viability test performed for BDI-AE@NMOF-808 in HeLa cells confirmed the nontoxic nature of the material and, more importantly, bioimaging applications have also been explored successfully.

Probing the Microsolvation Environment of the Green Fluorescent Protein Chromophore In Vacuo

We present vibrational and electronic photodissociation spectra of a model chromophore of the green fluorescent protein in complexes with up to two water molecules, prepared in a cryogenic ion trap at 160-180 K. We find the band origin of the singly hydrated chromophore at 20 985 cm^-1 (476.5 nm) and observe partially resolved vibrational signatures. While a single water molecule induces only a small shift of the S₁ electronic band of the chromophore, without significant change of the Franck-Condon envelope, the spectrum of the dihydrate shows significant broadening and a greater blue shift of the band edge. Comparison of the vibrational spectra with predicted infrared spectra from density functional theory indicates that water molecules can interact with the oxygen atom on the phenolate group or on the imidazole moiety, respectively.

Shape memory histocompatible and biodegradable sponges for subcutaneous defect filling and repair: greatly reducing surgical incision

Reducing surgical incision for large area subcutaneous defect filling and repair is a great challenge in the biomedical field, especially for plastic surgery. In this study, a novel hydroxyethyl cellulose/soy protein isolate (HEC/SPI) composite sponge (EHSS) with a fluid responsive shape memory property was constructed, whose thickness could be controlled by hot-pressing conditions to reduce the required surgical incision greatly. Effects of the main factors such as pressure, temperature and hot-pressing cycles on the recovery degree of EHSS were investigated systematically. The structure and physical properties of the sponges were characterized by FTIR spectroscopy, XRD, SEM etc. The results showed that EHSS could be pressed into thin disks with much smaller thickness, and the thickness retention ratio and recovery ratio were affected by hot-pressing conditions such as pressure and temperature. Especially, EHSS could be hot-pressed into a dense thin disk (EHSS-PT-130) at 130 °C with the pressure of 30 MPa, which could quickly recover its original shape by soaking in hydrophilic fluids. EHSS-PT-130 also exhibited good hydrophilicity, cytocompatibility, histocompatibility and in vivo biodegradability. Compared with the original EHSS, in vivo shape memory EHSS-PT-130 required much smaller surgical incision to reach the same repair effect and no need of extra sterilization, showing potential application for subcutaneous defect filling and repair.

Red-Shifted Substrates for FAST Fluorogen-Activating Protein Based on the GFP-Like Chromophores

A genetically encoded fluorescent tag for live cell microscopy is presented. This tag is composed of previously published fluorogen-activating protein FAST and a novel fluorogenic derivative of green fluorescent protein (GFP)-like chromophore with red fluorescence. The reversible binding of the novel fluorogen and FAST is accompanied by three orders of magnitude increase in red fluorescence (580-650 nm). The proposed dye instantly stains target cellular proteins fused with FAST, washes out in a minute timescale, and exhibits higher photostability of the fluorescence signal in confocal and widefield microscopy, in contrast with previously published fluorogen:FAST complexes.

Endo- and Exo-Functionalized Tetraphenylethylene M12L24 Nanospheres: Fluorescence Emission inside a Confined Space

The intrinsic relationship between the properties of green fluorescent protein (GFP) and its encapsulated small molecular light machine has spurred many biomimicking studies, aiming at revealing the detailed mechanism and further promoting its wide applications in different disciplines. However, how to build a similar confined microenvironment to mimic the cavity of a β-barrel and the fluorescence turn-on process is a fundamental challenge for both chemists and biologists. Herein, two distinct exo- and endo-functionalized tetraphenylethylene (TPE)-based M12L24 nanospheres with precise distribution of anchored TPE moieties and unique photophysical properties were constructed by means of a coordination-driven self-assembly strategy. Under dilute conditions, the nanospheres fluoresce more strongly than the corresponding TPE subcomponents. Meanwhile, the endo-functionalized sphere is able to induce a higher local concentration and more restrained motion of the enclosed 24 TPE units compared with exo-functionalized counterpart and thus induces much stronger emission due to the restriction of the rotation of the pendant TPE units. The biomimetic methodology developed here represents a promising way to understand and construct artificial GFP materials on the platforms of supramolecular coordination complexes.