A new pH sensitive fluorescent and white light emissive material through controlled intermolecular charge transfer

Anthocyanins of Delonix Regia Floral Petals: A Novel Approach on Fluorescence Enhancement, Forster Resonance Energy Transfer Mechanism and Photostability Studies for Optoelectronic Applications

In this work, we focused on extracting the anthocyanin dye in acetone, butanol, ethanol, and water solvents from Delonix regia flowers by a simple maceration extraction process. The identification of functional group analysis, vibrational studies, energy transfer mechanisms, optoelectronic properties, photostability studies, FRET-assisted potential light emissions and photometric properties of the anthocyanin dyes are successively investigated. FTIR spectroscopy and vibrational studies have confirmed the existence of polyphenolic groups in 2-phenyl chromenylium (anthocyanin) dyes. The optoelectronic results show the least direct bandgap (2.04 eV), indirect bandgap (1.55 eV), Urbach energy (0.380 eV), high refractive index (1.20), dielectric constant (2.794), and high optical conductivity (1.954 × 103 S/m) for the anthocyanin dye extracted found in water solvent. The photoluminescence properties such as Stoke's shift, high quantum yield, and lifetime results show that anthocyanin dyes are promising candidates for red-LEDs and optical materials. The absorption and emission spectra of the anthocyanin dyes follow the mirror image rule and the Franck-Condon factor exists between vibrational energy levels corresponding to all the electronic transitions. The excellent correspondence between the absorption and emission spectra reinforces that the anthocyanins are efficient (46%) FRET probes. Further, photometric properties such as CIE, CRI, CCT and colour purity results of anthocyanins in all studied solvents revealed that this material exhibits orange to red shades (x = 0.48 → 0.54 and y = 0.36 →0.45) and is well suitable for have great potential in the manufacturing of Organic-LEDs and other optoelectronic device applications.

Designing Thieno[3,4-c]pyrrole-4,6-dione Core-Based, A2-D-A1-D-A2-Type Acceptor Molecules for Promising Photovoltaic Parameters in Organic Photovoltaic Cells

Nonfullerene-based organic solar cells can be utilized as favorable photovoltaic and optoelectronic devices due to their enhanced life span and efficiency. In this research, seven new molecules were designed to improve the working efficiency of organic solar cells by utilizing a terminal acceptor modification approach. The perceived A2-D-A1-D-A2 configuration-based molecules possess a lower band gap ranging from 1.95 to 2.21 eV compared to the pre-existing reference molecule (RW), which has a band gap of 2.23 eV. The modified molecules also exhibit higher λmax values ranging from 672 to 768 nm in the gaseous and 715-839 nm in solvent phases, respectively, as compared to the (RW) molecule, which has λmax values at 673 and 719 nm in gas and chloroform medium, respectively. The ground state geometries, molecular planarity parameter, and span of deviation from the plane were analyzed to study the planarity of all of the molecules. The natural transition orbitals, the density of state, molecular electrostatic potential, noncovalent interactions, frontier molecular orbitals, and transition density matrix analysis of all studied molecules were executed to validate the optoelectronic properties of these molecules. Improved charge mobilities and dipole moments were observed, as newly designed molecules possessed lower internal reorganization energies. The open circuit voltage (Voc) of W4, W5, W6, and W7 among newly designed molecules was improved as compared to the reference molecule. These results elaborate on the superiority of these novel-designed molecules over the pre-existing (RW) molecule as potential blocks for better organic solar cell applications.

Stimuli-fluorochromic smart organic materials

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

Unraveling the Photoluminescence Properties of a Boron Nitride Nanosheet Dispersed in Different Solvents and Its Application to Generate White Light

Hexagonal boron nitride (h-BN) is an influential 2D nanomaterial; however, its practical optoelectronic applications rely primarily on controlling the structural defects. The photoluminescence depends explicitly on the developed vacancies and substitutional defects. The present work utilizes the concept of facile liquid-phase exfoliation of hexagonal (h) boron nitride (BN) powder in common organic solvents and cosolvent mixtures to obtain a layered boron nitride nanosheet (BNNS). Although the literature concerning the layered structure of BNNS obtained by different methods is substantial, what is lacking is a detailed photoluminescence study of the layered structure obtained by changing the solvent and cosolvent mixtures, and here lies the novelty of our work. The obtained layered structure was subjected to a detailed photoluminescence study by varying the temperature. We tried to correlate how the defects originating upon changing the solvent and cosolvent affected the photoluminescence of the layered BNNS. The obtained layered structure is suitably supported by optical and electron microscopy images. High-resolution transmission electron microscopy confirm the presence of a few layers, and X-ray photoelectron spectroscopy studies give an idea of the atomic composition of the obtained BNNS. The photoluminescence properties of the obtained BNNS in water were modulated by the addition of two different classes of block copolymers, e.g., Pluronic (F-68, P-407, and P-123) and Tetronic (T-904, T-908, and T-90R4) copolymers. As an application, we were successful in constructing a nanocomposite material made up of a BNNS-copolymer-organic fluorophore to check the possibilities of generating white light.

Multistimuli-Responsive Chromism of Vinylene-Linked Bisflavin Based on the Aggregation and Redox Properties

Multistimuli-responsive chromism was observed for vinylene-linked bisflavin 1 a with an extended π-conjugated platform. The yellow emission of a dilute solution of 1 a in CHCl₃ (0.2 mM) observed at 298 K under UV excitation was changed to orange or red emission upon (1) an increase of concentration, (2) a decrease of temperature, and (3) variation of the solvent. This is in contrast to the almost non stimuli-responsive chromism of the N-methylated bisflavin analogue 1 b and monoflavin 2 a. Mechanistic investigation by ¹ H NMR analysis under various conditions revealed that the extended π-conjugation platform and imide moiety of 1 a generate controllability in the formation of lower- and higher-ordered aggregates, which induce variation of the emission color upon change. Bisflavin 1 a also exhibited redox-induced chromism, where the orange emission of 1 a was quenched by the addition of hydrazine under anaerobic conditions, and changed back to the original emission upon subsequent bubbling of O₂ gas.

Multicolor-Luminescence Including White Light by Photomodulation of Supramolecular Assemblies in Aqueous Media

Photo-responsive supramolecular systems offer intriguing functional aspects which have led to their applications in diverse fields such as optoelectronics and biomedicine. However, the modulation of the luminescence output in a spatiotemporal fashion by photo-controlled transformation still remains a challenging task. Herein, we report the controlled regulation of the emission color of supramolecular assemblies of amphiphilic cyanostilbenes (CSs) in water through in situ photomodulation employing UV and sunlight. Due to their aggregation-induced emission (AIE) features, the CS chromophores in the supramolecular assemblies exhibited bright greenish-yellow emission. Photoirradiation predominantly led to the formation of a cyclized product exhibiting aggregation-caused quenching (ACQ) features and having efficient cyan-blue emission in water but severely quenched emission in the solid state. Hence, starting from a unicomponent scaffold, photomodulation provided tunable emission ranging from greenish-yellow to cyan-blue including white light in water. Furthermore, using the contrasting AIE and ACQ behavior of the components in the photoirradiated mixtures, we were able to design rewritable fluorescent inks and encryption in solid films indicating the practical utility of these systems.

Reversible Multilevel Stimuli-Responsiveness and Multicolor Room-Temperature Phosphorescence Emission Based on a Single-Component System

There are limited reports about the transformation of pure organic room-temperature phosphorescence (RTP) materials with multilevel stimuli-responsiveness at different RTP emission wavelengths under external stimuli. It is difficult to ensure efficient intersystem crossing (ISC) in different states of a single-component system. This research reports the conversion of the organic single-component small molecule 1,2-bis(4-alkoxyphenyl)ethane-1,2-dione (N-BOX) with multilevel stimuli-responsiveness between high-efficiency blue and yellow RTP by grinding or thermal annealing N-BOX crystals. The RTP emission of N-BOX in the crystalline state was easy to adjust by external stimuli (grinding or thermal annealing) due to its non-compact packing, which led to a phase transition and generated unique multilevel stimuli-responsiveness. In particular, the RTP quantum yield of 7-BOX with multilevel stimuli-responsiveness reached 68.4 %, which provides an opportunity for regulation of smart optical materials based on pure organic RTP.

Resolving fluorescence signatures of a photoconvertible fluorophore by fluorescence spectroscopy and MCR-ALS-based combinatorial approach

Photoconvertible fluorophores are important for a myriad of applications in chemistry and biology. Here, we spectrally resolve and quantify individual photophysical information of a dual-emitting photoconvertible fluorophore by fluorescence spectroscopy and multivariate curve resolution-alternate least square techniques. We found that the reactant fluorophore, which shows a weak locally excited (LE) emission and a dominant intramolecular charge transfer (ICT) emission, also exhibits an intermolecular charge transfer emission. The ICT emission bands of both the reactant and product fluorophores are originated from their respective LE states. The reactant fluorophore is a mixture of its different ground state conformers. Higher yields of photoconversion of the yellow-emitting reactant fluorophore are achieved via a visible light photoreaction, leading to formation of pure white light at an intermediate photoreaction time. These findings together help us to glean new photophysical and photochemical insights into the photoreaction of a dual-emitting photoconvertible fluorophore.

New white light-emitting halochromic stilbenes with remarkable quantum yields and aggregation-induced emission

Highly efficient single-component white light emitters (SWLEs), are attractive candidates for the simple and cost-effective fabrication of high-performance lighting devices. This study introduced a donor-π-acceptor and a donor-π-donor stilbene-based chromophores, representing pH-responsive fluorescence. The emitters showed yellow and green fluorescence in their neutral form. At the same time, protonation of the chromophores caused blue fluorescence color with a strong hypsochromic shift. The white light emission (WLE) for these chromophores was observed at approximately pH  3 due to the simultaneous presence of the neutral and protonated forms of the chromophores, covering almost all the emission spectra in the visible region (400-700 nm). These chromophores presented exceptional white light quantum yields (Φ) between 31 and 54%, which was desirable for producing white light-emitting devices. Density functional theory (DFT) and time-dependent (TD)-DFT were applied to study the structural and electronic properties of the chromophores.

Dark to bright fluorescence state by inter-connecting fluorophores: concentration-dependent blue to NIR emission and live cell imaging applications

Interconnected AIEgens produced concentration dependent tunable emission from blue to NIR.

[1]Benzothieno[3,2-b][1]benzothiophene-Based Dyes: Effect of Ancillary Moiety on Mechanochromism and Aggregation-Induced Emission

It is an established fact that [1]benzothieno[3,2-b][1]benzothiophene (BTBT) is a champion molecule for high mobility OFETs devices. Recently it is also utilized in dye-sensitized solar cells (DSSCs) and organic photovoltaics...

A tunable full-color lanthanide noncovalent polymer based on cucurbituril-mediated supramolecular dimerization

The construction of lanthanide multicolor luminescent materials with tunable photoluminescence properties has been developed as one of the increasingly significant topics and shown inventive applications in miscellaneous fields. However, fabricating such materials based on synergistically assembly-induced emission rather than simple blending of different fluorescent dyes together still remains a challenge. Herein, we report a europium-based noncovalent polymer with tunable full-color emission, which is constructed from the 2,6-pyridinedicarboxylic acid-bearing bromophenylpyridinium salt. This rationally designed bifunctional component can concurrently serve as a guest molecule and a chelating ligand to associate with cucurbit[8]uril and europium ions, thus leading to the formation of a trichromatic (red–green–blue, RGB) photoluminescent polypseudorotaxane-type noncovalent polymer in aqueous solution. Meanwhile, the full-color emission enclosed within the RGB color triangle could be readily produced by simply tuning the molar ratio of cucurbit[8]uril and europium ions. The lanthanide supramolecular polymer featuring tricolor emission, long lifetime, high photoluminescence efficiency and low cytotoxicity could be further applied in multicolor imaging in a cellular environment. These results provide a new and feasible strategy for the construction of full-color single lanthanide self-assembled nanoconstructs.

A lanthanide noncovalent polymer is constructed by integrating host–guest complexation and metal–ligand coordination, and can exhibit tunable trichromatic emission and multiple excited-state lifetimes under single wavelength excitation.

Shedding light on predicting and controlling emission chromaticity in multicomponent photoluminescent systems

Predictable colour tuning in multicomponent photoluminescent (PL) systems is achieved using mixtures of simultaneously emitting organic molecules. By mitigating the potential for energy transfer through the control of concentration, the resulting emission chromaticity of five dichromic PL systems is approximated as a linear combination of the emitting components and their corresponding brightness (χ i , ϕ i , and I ex,i ). Despite being limited to dilute solutions (10-6 M), colour tuning within these systems was controlled by (1) varying the composition of the components and (2) exploiting the differences in the components' excitation intensities at common wavelengths. Using this approach, white light emission (WLE) was realized using a pre-determined mixture of red, green, and blue emitting organic molecules. Based on these results, materials and devices with built-in or programmable emission colour can be achieved, including highly sought-after WLE.

Trialkylammonium salt degradation: implications for methylation and cross-coupling

Trialkylammonium (most notably N,N,N-trimethylanilinium) salts are known to display dual reactivity through both the aryl group and the N-methyl groups. These salts have thus been widely applied in cross-coupling, aryl etherification, fluorine radiolabelling, phase-transfer catalysis, supramolecular recognition, polymer design, and (more recently) methylation. However, their application as electrophilic methylating reagents remains somewhat underexplored, and an understanding of their arylation versus methylation reactivities is lacking. This study presents a mechanistic degradation analysis of N,N,N-trimethylanilinium salts and highlights the implications for synthetic applications of this important class of salts. Kinetic degradation studies, in both solid and solution phases, have delivered insights into the physical and chemical parameters affecting anilinium salt stability. ¹H NMR kinetic analysis of salt degradation has evidenced thermal degradation to methyl iodide and the parent aniline, consistent with a closed-shell S_N2-centred degradative pathway, and methyl iodide being the key reactive species in applied methylation procedures. Furthermore, the effect of halide and non-nucleophilic counterions on salt degradation has been investigated, along with deuterium isotope and solvent effects. New mechanistic insights have enabled the investigation of the use of trimethylanilinium salts in O-methylation and in improved cross-coupling strategies. Finally, detailed computational studies have helped highlight limitations in the current state-of-the-art of solvation modelling of reaction in which the bulk medium undergoes experimentally observable changes over the reaction timecourse.

The dual reactivity of N,N,N-trimethylanilinium salts towards arylation and methylation is decoupled in this mechanistic investigation to enable more strategic application of these salts in either reaction class.

Molecular conformational twist-controlled wide fluorescence tuning and white light emission in a single fluorophore via halochromism

Conformational differences-controlled fluorescence response of carbazole and triphenylamine appended cyano-pyridine donor–acceptor derivatives towards organic acids (TFA/PTSA).

A novel donor-π-acceptor halochromic 2,6-distyrylnaphthalene chromophore: synthesis, photophysical properties and DFT studies

In this study a new 2,6-distyryl naphthalene [2-((4-((E)-2-(6-((E)-2,4-bis(methylsulfonyl)styryl)naphthalen-2-yl)vinyl)phenyl)(ethyl)amino)ethan-1-ol; ASDSN] was synthesized successfully using Heck chemistry as the main reaction. The ASDSN compound is a donor-pi-acceptor (D-π-A) conjugated system with amino as electron donating and sulfonyl as electron withdrawing groups. The UV-vis absorption of ASDSN was observed in the range of 403-417 nm with high molar extinction coefficients (ε = 15 300-56 200 M-1 cm-1) in some different solvents. This new fluorescent 2,6-distyryl naphthalene compound emits in the yellow region of the visible spectrum (557 nm) with Stokes shifts of 5930 cm-1. ASDSN is a pH-responsive fluorescence compound that shows yellow fluorescence in neutral form and blue fluorescence in the protonated form. A white light emission (WLE) for the chromophore was observed at pH = 3.0. The ASDSN chromophore presented a satisfactory white light quantum yield (Φ) of 13% which was desirable for producing white light emitting devices. Density functional theory (DFT) and time-dependent (TD)-DFT were applied to study structural and electronic properties of the chromophore.

A novel near-infrared fluorescent probe with large stokes shifts for sensing extreme acidity and its application in bioimaging

In this work, we reported a novel near-infrared (NIR) fluorescent probe RQNN with large Stokes shift (98 nm) for monitoring pH under extremely acidic conditions. For the preparation of this probe, a 1,4-diethylpiperazine moiety was introduced in rhodamine scaffold to tune the electron-donating character, and an o-phenylenediamine was introduced in spironolactone to provide larger steric hindrance. The deprotonated-protonated equilibrium between RQNN, RQNN-H⁺ and RQNN-H⁺⁺ were evaluated in different pH by absorption and emission spectra. As expected, RQNN exhibited lower pk_a values (pk_a1 = 4.83, pk_a2 = 2.99), indicating that the probe can be used in extremely acidic pH. Moreover, RQNN possessed highly selective response to H⁺ over essential metal ions and biologically related redox molecules, high photo-stability, rapid response time, and excellent reversibility. Importantly, the probe had excellent cell membrane permeability and was further applied successfully to monitor pH fluctuations in live cells.

Photophysical Properties of a Donor-π-Acceptor Distyrylbenzene Derivative in Solution and Solid state

In this study, a π-conjugated organic compound based on distyrylbenzenes contains an amino substituent (as an electron-donor group) and a sulfone moiety (as an electron-withdrawing group) was investigated in the viewpoint of solvatochromism effects and the possibility of pH-sensitivity. This fluorescence dye (2-(ethyl(4-((E)-4-((E)-4-(methylsulfonyl)styryl)styryl)phenyl)amino)ethan-1-ol, ASDSB) showed Uv-Vis absorption in the range of 377-407 nm with high molar extinction coefficients (ε = 0.05 × 10⁵-1.05 × 10⁵ M^-1.cm^-1) in tested solvents with different polarities. This fluorescent compound emits in the region of visible spectrum (513-631 nm) with Stokes shifts of 5077.02-8912.66 cm^-1. The combination of ASDSB with poly(methyl methacrylate) (PMMA) and polyvinyl alcohol(PVA) polymers exhibits different photophysical properties which related to the polarity of polymers. By change of pH of dissolved ASDSB in methanol, a hypsochromic shift was observed. This phenomena is correspond to the change of chromophore upon protonation of amino group and its conversion to ammonium salt. In the case of solid samples, the bathochromic shifts (426-535 nm) were observed at the maximum emission wavelength for PMMA polymer. While no significant change in the maximum emission wavelength of ASDSB in PVA polymer were detected.

Single-Molecular White-Light Emitters and Their Potential WOLED Applications

White organic light-emitting diodes (WOLEDs) are superior to traditional incandescent light bulbs and compact fluorescent lamps in terms of their merits in ensuring pure white-light emission, low-energy consumption, large-area thin-film fabrication, etc. Unfortunately, WOLEDs based on multilayered or multicomponent (red, green, and blue (RGB)) emissive layers can suffer from some remarkable disadvantages, such as intricate device fabrication and voltage-dependent emission color, etc. Single molecules, which can emit white light, can be used to replace multiple emitters, leading to a simplified fabrication process, stable and reproducible WOLEDs. Recently, the performance of WOLEDs by using single molecules is catching up with that of the state-of-the-art devices fabricated by multicomponent emitters. Therefore, an increasing attention has been paid on single white-light-emitting materials for efficient WOLEDs. In this review, different mechanisms of white-light emission from a single molecule and the performance of single-molecule-based WOLEDs are collected and expounded, hoping to light up the interesting subject on single-molecule white-light-emitting materials, which have great potential as white-light emitters for illumination and lighting applications in the world.

Non-adiabatic Excited-State Molecular Dynamics: Theory and Applications for Modeling Photophysics in Extended Molecular Materials

Optically active molecular materials, such as organic conjugated polymers and biological systems, are characterized by strong coupling between electronic and vibrational degrees of freedom. Typically, simulations must go beyond the Born-Oppenheimer approximation to account for non-adiabatic coupling between excited states. Indeed, non-adiabatic dynamics is commonly associated with exciton dynamics and photophysics involving charge and energy transfer, as well as exciton dissociation and charge recombination. Understanding the photoinduced dynamics in such materials is vital to providing an accurate description of exciton formation, evolution, and decay. This interdisciplinary field has matured significantly over the past decades. Formulation of new theoretical frameworks, development of more efficient and accurate computational algorithms, and evolution of high-performance computer hardware has extended these simulations to very large molecular systems with hundreds of atoms, including numerous studies of organic semiconductors and biomolecules. In this Review, we will describe recent theoretical advances including treatment of electronic decoherence in surface-hopping methods, the role of solvent effects, trivial unavoided crossings, analysis of data based on transition densities, and efficient computational implementations of these numerical methods. We also emphasize newly developed semiclassical approaches, based on the Gaussian approximation, which retain phase and width information to account for significant decoherence and interference effects while maintaining the high efficiency of surface-hopping approaches. The above developments have been employed to successfully describe photophysics in a variety of molecular materials.

Triphenylamine-based stimuli-responsive solid state fluorescent materials

Molecular engineering of triphenylamine (TPA) units produced multi-stimuli-responsive solid state fluorescent materials.

Fluorescent 2-(Pyridin-2-yl)vinyl Pyridine Dyes and Their Thermocontrolled Release

The generation of unique thermosensitive fluorescent dyes via heteroaromatic Heck cross-coupling and N-pyridin-2-yl nucleophilic substitution was described. To demonstrate thermosensitive properties, the precursor was converted into carbonates or phosphates and heated at various temperatures and for various time periods. Significant changes in the fluorescence intensity and emission wavelengths, between carbonates and the cyclic product, were observed, and it was proved that the dyes may serve as removable fluorescent labels with large Stokes shifts (>80 nm). The application of thermosensitive fluorescent dyes in oligonucleotide labeling has been demonstrated.

Solvatochromism and mechanochromism observed in a triphenylamine derivative

A donor-π-acceptor fluorescent dye, 4-[N,N-di(4-phenyl)amino]benzaldehyde 4-chlorobenzoyl hydrazone (TPA-CBH), based on a triphenylamine derivative (TPA) and 4-chlorobenzoyl hydrazine (CBH) was designed and synthesized. The optical properties of this luminogen were investigated in solutions as well as in the solid states. In the intramolecular charge-transfer (CT) mechanism, TPA-CBH exhibits solvatochromism when dissolved in various polar solvents. Aggregation-induced emission was observed with the changes of tetrahydrofuran/water ratios. In the solid state, mechanochromic fluorescence is observed when the samples are stressed under different conditions. Based on structural analyses and theoretical calculations, it is found that intra- and intermolecular CT processes play a key role in the diversity of fluorescent properties.

White Light Emission from a Simple Mixture of Fluorescent Organic Compounds

Three fluorescent organic compounds—furocoumarin (FC), dansyl aniline (DA), and 7-hydroxycoumarin-3-carboxylic acid (CC)—are mixed to produce almost pure white light emission (WLE). This novel mixture is immobilised in silica aerogel and applied as a coating to a UV LED to demonstrate its applicability as a low-cost, organic coating for WLE via simultaneous emission. In ethanol solution and when immobilised in silica aerogel, the mixture exhibits a Commission Internationale d’Eclairage (CIE) chromaticity index of (0.27, 0.33). It was observed that a broadband and simultaneous emission involving coumarin carboxylic acid, furocoumarin and dansyl aniline played a vital role in obtaining a CIE index close to that of pure white light.

Multiphotoluminescence from a Triphenylamine Derivative and Its Application in White Organic Light-Emitting Diodes Based on a Single Emissive Layer

White organic light-emitting diode (WOLED) technology has attracted considerable attention because of its potential use as a next-generation solid-state lighting source. However, most of the reported WOLEDs that employ the combination of multi-emissive materials to generate white emission may suffer from color instability, high material cost, and a complex fabrication procedure which can be diminished by the single-emitter-based WOLED. Herein, a color-tunable material, tris(4-(phenylethynyl)phenyl)amine (TPEPA), is reported, whose photoluminescence (PL) spectrum is altered by adjusting the thermal annealing temperature nearly encompassing the entire visible spectra. Density functional theory calculations and transmission electron microscopy results offer mechanistic understanding of the PL redshift resulting from thermally activated rotation of benzene rings and rotation of 4-(phenylethynyl) phenyl)amine connected to the central nitrogen atom that lead to formation of ordered molecular packing which improves the π-π stacking degree and increases electronic coupling. Further, by precisely controlling the annealing time and temperature, a white-light OLED is fabricated with the maximum external quantum efficiency of 3.4% with TPEPA as the only emissive molecule. As far as it is known, thus far, this is the best performance achieved for single small organic molecule based WOLED devices.

Humidity- and Temperature-Tunable Multicolor Luminescence of Cucurbit[8]uril-Based Supramolecular Assembly

Fabrication of tunable luminescent materials by a single luminophore is a challenge owning to the limit of emissive properties of monofluorophores. Herein, a type of temperature and humidity dual-responsive luminescent material based on host-guest supramolecular self-assembly was developed. Included into the cavity of cucurbit[8]uril (CB[8]) to form a 1:2 host-guest binding motif, the highly blue-emissive thiazolothiazole methyl-viologen (TMV) molecules were promoted to stack closely with a sharp luminescence decrease at 460 nm and rise of the dimer emission at 535 nm, especially at high concentrations in aqueous solution, which was demonstrated by fluorescence spectra, UV-vis absorbance spectra, NMR, and ITC data. Accordingly, when printed on paper, the 1/2 CB[8]/TMV complex presented a reversibly humidity-dependent emissive behavior with luminescent color changing from greenish-yellow in wet to blue upon evaporation. Besides, the  sensitivity of the host-guest interaction endowed the CB[8]/TMV complexes with temperature-tunable emission which showed a considerably enhanced blue luminescence at higher temperature. Subsequently, a ratiometric temperature-responsive emitter which luminesced reversibly from pink to white and then to blue light at temperature ranging from 0 to 70 °C was fabricated by mixing the CB[8]/TMV complex with thermal-sensitized emitting GSH-Au nanoclusters. These fine-tuning abilities make the CB[8]/TMV supramolecular complex applicable in visual luminescent devices such as anti-counterfeiting labels and fluorescent thermometers.

Synthesis and photophysical studies on 2‑styryl phenanthro[9,10‑d]oxazole derivatives

A new series of 2‑styryl phenanthro[9,10‑d]oxazoles was readily accessible from the condensation reaction of 9,10‑phenanthroquinone with cinnamaldehydes in the presence of lactic acid. All these styryl dyes were isolated in good yields and characterized by various analytical and spectroscopic techniques. One of the dyes containing NO₂ group (3d) was structurally characterized by single crystal X-ray analysis. These dyes displayed emission in blue to green region with larger Stokes shift values characteristic to the nature of substituents. In addition, positive solvatochromic trend was observed by increasing the solvent polarity suggestive of a more stabilized polar excited state. Moreover, the addition of trifluoroacetic acid leads to a prominent blue-shift in visible and emission color changes owing to the protonation of the nitrogen atom of oxazole moiety. Among the all, the oxazole derivative having NMe₂ group (3b) exhibits good response to acidic pH in the range of 3.0 to 5.6 with a good linearity upon decreasing the pH from 8.0 to 2.16. The absorption studies were further supported by density functional theory calculations.

Aggregation-Induced Emission and White Luminescence from a Combination of π-Conjugated Donor-Acceptor Organic Luminogens

Two new star-shaped phenyl- and triazine-core based donor-acceptor (D-A) type conjugated molecules bearing triphenylamine end-capped arms were synthesized and characterized as imminent organic optoelectronic materials. Photophysical properties of the compounds were explored systematically via spectroscopic and theoretical methods. Because of the presence of donor-acceptor interactions, these luminogens display multifunctional properties, for instance, high extinction coefficient, large stokes shift, and pronounced solvatochromic effect. The compounds also exhibited phenomenon known as aggregation-induced emission on formation of nano-aggregates in the tetrahydrofuran-water mixture. The aggregate formation was confirmed by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering analyses. Moreover, by controlling the electron withdrawing ability of the acceptor, complementary emissive fluorophores (blue and yellow) were achieved. These two complementary colors together span the entire range of visible spectrum (400-800 nm) and therefore when mixed in a requisite proportion generate white light in solution phase. These findings have potential for the progress of new organic white light radiating materials for applications in lighting and display devices.

Facile Synthesis of a Terephthalic Acid-Based Organic Fluorophore with Strong and Color-Tunable Emission in Both Solution and Solid States for LED Applications

Dual-state emission (DSE) fluorophores with strong photoluminescence in both solution and solid states have wide applications in fluorescent probes and photoelectric devices. However, most of the existing DSE fluorophores involve complex synthetic strategies or only one or two emission colors in the solid state, which may hinder their practical applications. Herein, we report a facile and effective strategy to fabricate a kind of novel adjustable DSE fluorophore TPAA-Cu based on the small molecule terephthalic acid (TPA) and ascorbic acid (AA) with CuCl₂ as the catalyst. Not only can the TPAA-Cu solution emit blue, blue-green, and yellow colors depending upon the pH of solution, but also it shows reversible pH-tunable fluorescence colors. More importantly, corresponding TPAA-Cu solid fluorophores with blue, blue-green, and yellow colors can also be obtained with the quantum yields of 16.3, 26.7, and 29.6%, respectively.

Conjugation of Amphiphilic Proteins to Hydrophobic Ligands in Organic Solvent

Protein-ligand conjugations are usually carried out in aqueous media in order to mimic the environment within which the conjugates will be used. In this work, we focus on the conjugation of amphiphilic variants of elastin-like polypeptide (ELP), short elastin (sEL), to poorly water-soluble compounds like OPPVs ( p-phenylenevinylene oligomers), triarylamines, and polypyridine-metal complexes. These conjugations are problematic when carried out in aqueous phase because hydrophobic ligands tend to avoid exposure to water, which in turn causes the ligand to self-aggregate and/or interact noncovalently with hydrophobic regions of the amphiphile. Ultimately, this behavior leads to low conjugation efficiency and contamination with strong noncovalent "conjugates". After exploring the solubility of sEL in various organic solvents, we have established an efficient conjugation methodology for obtaining covalent conjugates virtually free of contaminating noncovalent complexes. When conjugating carboxylated ligands to the amphiphile amines, we demonstrate that even when only one amine (the N-terminus) is present, its derivatization is 98% efficient. When conjugating amine moieties to the amphiphile carboxyls (a problematic configuration), protein multimerization is avoided, 98-100% of the protein is conjugated, and the unreacted ligand is recovered in pure form. Our syntheses occur in "one pot", and our purification procedure is a simple workup utilizing a combination of water and organic solvent extractions. This conjugation methodology might provide a solution to problems arising from solubility mismatch of protein and ligand, and it is likely to be widely applied for modification of recombinant amphiphiles used for drug delivery (PEG-antibodies, polymer-enzymes, food proteins), cell adhesion (collagen, hydrophobins), synthesis of nanostructures (peptides), and engineering of biocompatible optoelectronics (biological polymers), to cite a few.

A review: the trend of progress about pH probes in cell application in recent years

Intracellular pH values are some of the most important factors that govern biological processes and the acid-base homeostasis in cells, body fluids and organs sustains the normal operations of the body. Subcellular organelles including the acidic lysosomes and the alkalescent mitochondria undergo various processes such as intracellular digestion, ATP production and apoptosis. Due to their precise imaging capabilities, fluorescent probes have attracted great attention for the illustration of pH modulated processes. Furthermore, based on the unique acidic extracellular environment of acidic lysosomes, fluorescent probes can specifically be activated in cancer cells or tumors. In this review, recently reported lysosome and mitochondria specific pH imaging probes as well as pH-activatable cancer cell-targetable probes have been discussed.

Two novel AIEE-active imidazole/ α-cyanostilbene derivatives: photophysical properties, reversible fluorescence switching, and detection of explosives

Novel imidazole derivatives containing the α-cyanostilbene unit can act as reversible acid/base stimulated fluorescence switches in the solid state, as chemosensors for explosives detection in aqueous systems, and as test strip detectors.

Secondary inner filter effect allows extremely efficient pure white light emission by spatially separated organic fluorophores

White light emission with 70 ± 3% efficiency under dilute conditions was obtained via the secondary inner filter effect between 2-(1-pyrenyl)benzimidazole (PyBIM) and pyrelene monoimide (PMI).

π-Extended fluoranthene imide derivatives: synthesis, structures, and electronic and optical properties

Diels–Alder reactions of acenaphthylene-5,6-dicarboximide (AI) derivatives with the corresponding dienes afforded some derivatives of π-extended fluoranthene imide, namely N-(2-ethylhexyl)-7,10-diphenylfluoranthene imide (DPFI) and N-(2-ethylhexyl)-7,8,9,10-tetraphenylfluoranthene imide (TPFI), N-(n-octyl)-benzo[k]fluoranthene imide (BFI), and N-(n-octyl)-naphtho[k]fluoranthene imide (NFI). Molecular structures of TPFI and BFI reveal that the core π-skeletons have a highly planar structure, and the molecules form a dimeric structure in the crystals. The absorption spectra exhibit bathochromic shift with π-extension of the core π-skeletons. On the other hand, DPFI and TPFI show the long-wavelength emission related to BFI, probably due to π-extension toward the phenyl substituents in the excited states. BFI and NFI exhibited an interesting concentration-dependent 1H-NMR behavior in CDCl3, suggesting self-aggregation formation. Moreover, BFI and NFI show moderate and remarkable solvatofluorochromism in solutions (BFI for ΔλEM = 67 nm, NFI for ΔλEM = 116 nm), respectively, while DPFI and TPFI show weak solvatofluorochromism. The density functional theory calculations demonstrate that the considerable spatial separation between the HOMO and LUMO coefficients in the NFI molecule. The result indicates that the ground-to-excited state transition of NFI should have intramolecular charge transfer (ICT) character.

Selective Binding of Genomic Escherichia coli DNA with ZnO Leads to White Light Emission: A New Aspect of Nano-Bio Interaction and Interface

Here, we report for the first time, a novel and intriguing application of deoxyribonucleic acid (DNA) in the area of optics by demonstrating white light emission by tuning the emission of a nanomaterial, ZnO rods, exhibiting surface defects, in the presence of genomic Escherichia coli DNA with a comparatively high quantum efficiency. In order to understand the DNA specificity, we have also studied the interaction of ZnO with CT, and ML DNA, ss EC DNA, synthetic polynucleotides and different mononucleosides and bases. Further, in order to understand the effect of particle shape and defects present in ZnO, we have also extended our study with ZnO rods prepared at higher temperature exhibiting red emission and ZnO particles exhibiting yellow emission. Interestingly, none of the above studies resulted in white light emission from ZnO-DNA complex. Our studies unequivocally confirmed that the concentration and the nature of DNA and ZnO together plays a crucial role in obtaining CIE coordinates (0.33, 0.33) close to white light. The much enhanced melting temperature (T_m) of EC DNA and the energetics factors confirm enhanced hydrogen bonding of ZnO with EC DNA leading to a new emission band. Our experimental observations not only confirm the selective binding of ZnO to EC DNA but also open a new perspective for developing energy saving light emitting materials through nano-bio interactions.

Synthesis and optical and electrochemical properties of julolidine-structured pyrido[3,4-b]indole dye

The julolidine-structured pyrido[3,4-b]indole dye ET-1 possesses the ability to act as a calorimetric and fluorescent sensor for Brønsted and Lewis acids.

Crystallization-induced reversible fluorescence switching of alkyl chain length dependent thermally stable supercooled organic fluorescent liquids

Triphenylamine fluorophore-produced alkyl chain length dependent stable fluorescent liquids and their crystallization-induced reversible fluorescence switching.

Halochromic Isoquinoline with Mechanochromic Triphenylamine: Smart Fluorescent Material for Rewritable and Self-Erasable Fluorescent Platform

Halochromic isoquinoline attached mechanochromic triphenylamine, N-phenyl-N-(4-(quinolin-2-yl)phenyl)benzenamine (PQPBA) and tris(4-(quinolin-2-yl)phenyl)amine (TQPA), smart fluorescent materials exhibit thermo/mechanochromism and tunable solid state fluorescence and their unusual halochromic response in PMMA matrix have been used for fabricating rewritable and self-erasable fluorescent platforms. PQPBA and TQPA showed strong fluorescence in solution (Φ_f = 0.9290 (PQPBA) and 0.9160 (TQPA)) and moderate solid state fluorescence (Φ_f = 20 (PQPBA) and 17% (TQPA). Interestingly, they exhibited a rare temperature (0-100 °C) dependent positive fluorescence enhancement via activating radiative vibrational transition. The deaggregation of PQPBA and TQPA in PMMA polymer matrix lead to the enhancement of fluorescence intensity strongly and fabricated strong blue fluorescent thin films (Φ_f = 58% (PQPBA) and 54% (TQPA). The halochromic isoquinoline has been exploited for demonstrating reversible off-on fluorescence switching by acid (TFA (trifluoroacetic acid)/HCl) and base (NH₃) treatment in both solids as well as PMMA thin films. Importantly, rewritable and self-erasable fluorescent platform has been achieved by make use of unusual fluorescence responses of PQPBA/TQPA with TFA/HCl after exposing NH₃. Single crystal and powder X-ray diffraction (PXRD) studies provided the insight on the solid-state fluorescence and external stimuli-induced fluorescence changes.

White-light emission from a single heavy atom-free molecule with room temperature phosphorescence, mechanochromism and thermochromism

Two heavy atom-free white-light emitting luminophores exhibit fluorescence–phosphorescence dual-emission and are multi-stimuli responsive at room temperature.

Two heavy atom-free luminophores (SHB₂t and SDB₂t) with simple molecular structures have been synthesized via Suzuki coupling reactions in which both display white-light emission with prompt fluorescence and room temperature phosphorescence (RTP) in the solid state. The impressive RTP of the luminophores is produced by a synergistic effect of the strong intermolecular hydrogen bonding in addition to the spin–orbit coupling of the sulfonyl oxygen atoms and the moderate singlet-triplet energy gaps (ΔE_ST). These factors facilitate the intersystem crossing (ISC) process to generate triplet excitons in which the molecular conformations become immobilized to effectively suppress radiationless decay. Under the stimuli of mechanical force and solvent vapor, the RTP of SHB₂t and SDB₂t can be simply turned off and on by breaking and reforming the robust hydrogen bonding, which leads to remarkable and reversible mechanochromism between white and deep-blue emission. Moreover, two different thermochromic processes have been observed for the pristine and ground samples of SDB₂t, in which a tricolor switching system between white, deep-blue and blue emission has been successfully achieved through the sequential control of grinding, heating and fuming. From detailed studies we have determined that the mechanism for the thermochromism of SDB₂t is correlated with the rearrangement of the white-light emitting molecules to a new packing mode without RTP emission.