Energy and Electron Transfer Dynamics within a Series of Perylene Diimide/Cyclophane Systems

Unraveling the Origin of Multichannel Circularly Polarized Luminescence in a Pyrene-Functionalized Topologically Chiral [2]Catenane

Mechanically interlocked molecules (MIMs) are promising platforms for developing functionalized artificial molecular machines. The construction of chiral MIMs with appealing circularly polarized luminescence (CPL) properties has boosted their potential application in biomedicine and the optical industry. However, there is currently little knowledge about the CPL emission mechanism or the emission dynamics of these related MIMs. Herein, we demonstrate that time-resolved circularly polarized luminescence (TRCPL) spectroscopy combined with transient absorption (TA) spectroscopy offers a feasible approach to elucidate the origins of CPL emission in pyrene-functionalized topologically chiral [2]catenane as well as in a series of pyrene-functionalized chiral molecules. For the first time, direct evidence differentiating the chiroptical signals originating from either topological (local state emission) or Euclidean chirality (excimer state emission) in these pyrene-functionalized chiral molecules has been discovered. Our work not only establishes a novel and ideal approach to study CPL mechanism, but also provides a theoretical foundation for the rational design of novel chiral materials in the future.

Guest-Mediated Modulation of Photophysical Pathways in a Coronene Bisimide Cyclophane

The properties and functions of chromophores utilized by nature are strongly affected by the environment formed by the protein structure in the cells surrounding them. This concept is transferred here to host-guest complexes with the encapsulated guests acting as an environmental stimulus. A new cyclophane host based on coronene bisimide is presented that can encapsulate a wide variety of planar guest molecules with binding constants up to (4.29 ± 0.32) × 1010 M-1 in chloroform. Depending on the properties of the chosen guest, the excited state deactivation of the coronene bisimide chromophore can be tuned by the formation of host-guest complexes toward fluorescence, exciplex formation, charge separation, room-temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). The photophysical processes were investigated by UV/vis absorption, emission, and femto- and nanosecond transient absorption spectroscopy. To enhance the TADF, two different strategies were used by employing suitable guests: the reduction of the singlet-triplet gap by exciplex formation and the external heavy atom effect. Altogether, by using supramolecular host-guest complexation, a versatile multimodal chromophore system is achieved with the coronene bisimide cyclophane.

Dynamics of reduced perylene bisimide cyclophane redox species by ultrafast spectroelectrochemistry

Charged molecules play essential roles in many natural and artificial functional processes, ranging from photosynthesis to photovoltaics to chemical reactions and more. It is often difficult to identify the optical dynamic properties of relevant redox species because they cannot be easily prepared, their spectra overlap, or they evolve on a femtosecond timescale. Here, we address these challenges by combining spectroelectrochemistry, ultrafast transient absorption spectroscopy, and suitable data analysis. We illustrate the method with the various redox species of a cyclophane composed of two perylene bisimide subunits. While singular-value decomposition is a well-established tool in the analysis of time-dependent spectra of a single molecular species, we here use it additionally to separate transient maps of individual redox species. This is relevant because at any specific applied electrochemical potential, several redox species coexist in the ensemble, and our procedure allows disentangling their spectroscopic response. In the second step, global analysis is then employed to retrieve the excited-state lifetimes and decay-associated difference spectra. Our approach is generally suitable for unraveling ultrafast dynamics in materials featuring charge-transfer processes.

Viologen-based ionic conjugated mesoporous polymer as the electron conveyer for efficient polysulfide trapping and conversion

The commercialization of lithium-sulfur (Li-S) batteries has been hindered by the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs). Herein, we reported a viologen-based ionic conjugated mesoporous polymer (TpV-Cl), which acts as the cathode host for modifying Li-S batteries. The viologen component serves as a reversible electron conveyer, leading to a comprehensive enhancement in the adsorption of polysulfides and improved conversion rate of polysulfides during the electrochemical process. As a result, the S@TpV-PS cathode exhibits outstanding cycling performance, achieving 300 cycles at 2.0 C (1 C = 1675 mA g-1) with low decay rate of 0.032% per cycle. Even at a high sulfur loading of 4.0 mg cm-2, S@TpV-PS shows excellent cycling stability with a Coulombic efficiency of up to 98%. These results highlight the significant potential of S@TpV-PS in developing high-performance Li-S batteries.

Polymerization Based on Modified β-Cyclodextrin Achieves Efficient Phosphorescence Energy Transfer for Anti-Counterfeiting

Supramolecular polymerization can not only activate guest phosphorescence, but also promote phosphorescence Förster resonance energy transfer and induce effective delayed fluorescence. Herein, the solid supramolecular assemblies of ternary copolymers based on acrylamide, modified β-cyclodextrin (CD), and carbazole (CZ) are reported. After doping with polyvinyl alcohol (PVA) and dyes, a NIR luminescence supramolecular composite with a lifetime of 1.07 s, an energy transfer efficiency of up to 97.4% is achieved through tandem phosphorescence energy transfer. The ternary copolymers can realize macrocyclic enrichment of dyes in comparison to CZ and acrylamide copolymers without CD, which can facilitate energy transfer between triplet and singlet with a high donor-acceptor ratio. Additionally, the flexible polymeric films exhibit regulable lifetime, tunable luminescence color, and repeatable switchable afterglow by adjusting the excitation wavelength, donor-acceptor ratio, and wet/dry stimuli. The luminescence materials are successfully applied to information encryption and anti-counterfeiting.

Exciplex Emission and Förster Resonance Energy Transfer in Polycyclic Aromatic Hydrocarbon-Based Bischromophoric Cyclophanes and Homo[2]catenanes

Energy transfer and exciplex emission are not only crucial photophysical processes in many living organisms but also important for the development of smart photonic materials. We report, herein, the rationally designed synthesis and characterization of two highly charged bischromophoric homo[2]catenanes and one cyclophane incorporating a combination of polycyclic aromatic hydrocarbons, i.e., anthracene, pyrene, and perylene, which are intrinsically capable of supporting energy transfer and exciplex formation. The possible coconformations of the homo[2]catenanes, on account of their dynamic behavior, have been probed by Density Functional Theory calculations. The unique photophysical properties of these exotic molecules have been explored by steady-state and time-resolved absorption and fluorescence spectroscopies. The tetracationic pyrene-perylene cyclophane system exhibits emission emanating from a highly efficient Förster resonance energy transfer (FRET) mechanism which occurs in 48 ps, while the octacationic homo[2]catenane displays a weak exciplex photoluminescence following extremely fast (<0.3 ps) exciplex formation. The in-depth fundamental understanding of these photophysical processes involved in the fluorescence of bischromophoric cyclophanes and homo[2]catenanes paves the way for their use in future bioapplications and photonic devices.

Effects of the Solvent Vapor Exposure on the Optical Properties and Photocatalytic Behavior of Cellulose Acetate/Perylene Free-Standing Films

The search to deliver added value to industrialized biobased materials, such as cellulose derivatives, is a relevant aspect in the scientific, technological and innovation fields at present. To address these aspects, films of cellulose acetate (CA) and a perylene derivative (Pr) were fabricated using a solution-casting method with two different compositions. Consequently, these samples were exposed to dimethylformamide (DMF) solvent vapors so that its influence on the optical, wettability, and topographical properties of the films could be examined. The results demonstrated that solvent vapor could induce the apparent total or partial preferential orientation/migration of Pr toward the polymer-air interface. In addition, photocatalytic activities of the non-exposed and DMF vapor-exposed films against the degradation of methylene blue (MB) in an aqueous medium using light-emitting diode visible light irradiation were comparatively investigated. Apparently, the observed improvement in the performance of these materials in the MB photodegradation process is closely linked to the treatment with solvent vapor. Results from this study have allowed us to propose the fabrication and use of the improved photoactivity "all-organic" materials for potential applications in dye photodegradation in aqueous media.

Perylene-Based Smart Fluoroprobe with Dual Function: Ratiometric Response toward Hazardous Organic Peroxides and Pure White Light Generation via Self-Assembly

In this report, we have designed and synthesized a perylene-based smart fluoroprobe (PBE) in which the perylene core has been functionalized with the boronate group at the peri-position. PBE shows a very fast and ratiometric response toward harmful organic peroxides (OPs) generated in old ethereal solvents via auto-oxidation. The response toward OPs takes place with a visible color change from green to yellow, which could be easily observed with the naked eye. The reaction between PBE and OPs involves the cleavage of the boronate group and its consequent conversion into the -OH group. The response of PBE toward OPs was monitored using UV-vis absorption, fluorescence emission, IR spectroscopy, and mass spectrometry. Additionally, we have also explored the self-assembly of PBE in an organic-aqueous solvent mixture, which shows pure white light emission (WLE) with the CIE coordinates (0.33, 0.33) in a 50% dimethyl sulfoxide-water mixture. This work clearly reveals that PBE fluoroprobe can be employed for sensitive detection of hazardous OPs present in old ethereal solvents. Moreover, the ability of PBE to generate the perfect pure WLE makes it a potential candidate for application in organic light-emitting devices.

Incorporating Fe, Co co-doped graphene with PDI supermolecular for promoted photocatalytic activity: A story of electron transfer

Iron-cobalt dual single-atom anchoring on nitrogen-doped graphene (Fe_xCo_y-NG) improves the efficiency of migration and separation of photo-generated carriers. In this work, the perylene diimide (PDI) is self-assembled on the Fe_xCo_y-NG to form the Fe_xCo_y-NG/PDI composites by π-π interaction, which is reported for the first time. The bisphenol A (BPA) degradation of optimized 20% Fe_0.2Co_0.8-NG/PDI are nearly 100%, and the degradation rate is 1.5 and 12.7 times that of the self-assembled PDI and commercial-grade PDI. The high degradation performance by Fe_xCo_y-NG/PDI are mainly due to: (i) regulating the proportion of Fe-Co dual active sites content, so that it can achieve the synergistic interaction to facilitate the transfer of electrons in the catalytic reaction. (ii) PDI is uniformly dispersed by adding the Fe_xCo_y-NG, which increases the specific surface area of composites to adsorb more pollutants. Free radical trapping experiments and electron spin-resonance spectroscopy characterization confirmed that the O₂^-, OH, ¹O₂ and h⁺ are the main reactive species (RSs) for BPA degradation. Under the attack of RSs, BPA completes the processes of hydroxylation, demethylation, aromatization, ring-opening, and finally complete mineralization into CO₂ and H₂O. These results revealed that Fe_0.2Co_0.8-NG/PDI photocatalysts may be efficiently applied for the remediation of phenol contaminated natural waters.

Covalent post-assembly modification of π-conjugated supramolecular polymers delivers structurally robust light-harvesting nanoscale objects

A two-component stapling strategy is used to covalently tether a new class of water-soluble supramolecular polymers built from bay-functionalized perylene bisimide (PBI) units. By leveraging a novel combined strategy where excitonic coupling and fluorescence data are exploited as spectroscopic reporters, structural design principles are established to form light-harvesting superstructures whose ground-state electronic properties are not sensitive to solvation environments. Moreover, we interrogate the structural properties of stapled superstructures by capitalizing on the drastic changes in fluorescence quantum yields against parent supramolecular assemblies. In essence, our work shows that the combination of excitonic coupling measurements and photoluminescence experiments delineates a more accurate understanding of the design principles required to limit the degree of structural defects and magnify short- and long-range electronic couplings between redox-active units in this new class of solvated nanoscale objects. These results highlight that the fragile conformation of non-covalent assemblies, which are regulated by weak secondary interactions, can be preserved by post-assembly modification of preformed supramolecular polymers. These synthetic and spectroscopic principles can in turn be codified as experimental handles to parameterize the optoelectronic properties of light-harvesting nanoscale objects.

Alkoxy-Substituted Quadrupolar Fluorescent Dyes

Polar and polarizable π-conjugated organic molecules containing push-pull chromophores have been investigated extensively in the past. Identifying unique backbones and building blocks for fluorescent dyes is a timely exercise. Here, we report the synthesis and characterization of a series of fluorescent dyes containing quadrupolar A-D-A constitutions (where A = acceptor and D = donor), which exhibit fluorescence emission at a variety of different wavelengths. We have investigated the effects of different electron-withdrawing groups, located at both termini of a para-terphenylene backbone, by steady-state UV/vis and fluorescence spectroscopy. Pyridine and substituted pyridinium units are also introduced during the construction of the quadrupolar backbones. Depending on the quadrupolarity, fluorescence emission wavelengths cover from 380 to 557 nm. Time-resolved absorption and emission spectroscopy reveal that the photophysical properties of those quadrupolar dyes result from intramolecular charge transfer. One of the dyes we have investigated is a symmetrical box-like tetracationic cyclophane. Its water-soluble tetrachloride, which is non-cytotoxic to cells up to a loading concentration of 1 μM, has been employed in live-cell imaging. When taken up by cells, the tetrachloride emits a green fluorescence emission without any hint of photobleaching or disruption of normal cell behavior. We envision that our design strategy of modifying molecules through the functionalization of the quadrupolar building blocks as chromophores will lead to future generations of fluorescent dyes in which these A-D-A constitutional fragments are incorporated into more complex molecules and polymers for broader photophysical and biological applications.

Concepts and principles of self-n-doping in perylene diimide chromophores for applications in biochemistry, energy harvesting, energy storage, and catalysis

Self-doping is an essential method of increasing carrier concentrations in organic electronics that eliminates the need to tailor host-dopant miscibility, a necessary step when employing molecular dopants. Self-n-doping can be accomplished using amines or ammonium counterions as an electron source, which are being incorporated into an ever-increasingly diverse range of organic materials spanning many applications. Self-n-doped materials have demonstrated exemplary and, in many cases, benchmark performances in a variety of applications. However, an in-depth review of the method is lacking. Perylene diimide (PDI) chromophores are an important mainstay in the semiconductor literature with well-known structure-function characteristics and are also one of the most widely utilized scaffolds for self-n-doping. In this review, we describe the unique properties of self-n-doped PDIs, delineate structure-function relationships, and discuss self-n-doped PDI performance in a range of applications. In particular, the impact of amine/ammonium incorporation into the PDI scaffold on doping efficiency is reviewed with regard to attachment mode, tether distance, counterion selection, and steric encumbrance. Self-n-doped PDIs are a unique set of PDI structural derivatives whose properties are amenable to a broad range of applications such as biochemistry, solar energy conversion, thermoelectric modules, batteries, and photocatalysis. Finally, we discuss challenges and the future outlook of self-n-doping principles.

Water-soluble thienoviologen derivatives for imaging bacteria and antimicrobial photodynamic therapy

A series of water-soluble cationic thienoviologen derivative photosensitizers (nTPy-Rs) for photodynamic therapy (PDT) is reported. Cationic pyridine groups were introduced into the thiophene framework to enhance solubility and bacteria-binding ability, which effectively improved bacteriological imaging and antibacterial activity. The optoelectronic properties of nTPy-Rs were regulated by adjusting the number of thiophene groups, and the differences in antibacterial activity due to the functional scaffolds were compared. The results showed that nTPy-Rs could generate reactive oxygen species (ROS, including macroscopic free radicals), efficiently inhibit bacterial growth, and achieve the minimum inhibitory concentration (MIC) to the ng mL^-1 level. Remarkably, 2TPyC6, containing two thiophene groups and modified by alkyl side chains, showed the best bacteriostatic performance, with the MIC of 20 ng mL^-1 and 4.5 ng mL^-1 for E. coli and S. aureus, respectively, which are the lowest photosensitizer concentrations used in PDT to date. The low cell cytotoxicity and excellent antibacterial performance give nTPy-Rs great potential as PDT agents in vivo.

Symmetry-Breaking Charge Separation in Phenylene-Bridged Perylenediimide Dimers

Perylenediimides (PDIs) are important molecular building blocks that are being investigated for their applicability in optoelectronic technologies. Covalently linking multiple PDI acceptors at the 2,5,8,11 (headland) positions adjacent to the PDI carbonyl groups is reported to yield higher power conversion efficiencies in photovoltaic cells relative to PDI acceptors linked at the 1,6,7,12 (bay) positions. While the photophysical properties of PDIs linked via the bay positions have been investigated extensively, those linked at the headland positions have received far less attention. We showed previously that symmetry-breaking charge separation (SB-CS) in PDIs hold promise as a strategy for increasing photovoltaic efficiency. Here we use transient absorption and emission spectroscopies to investigate the competition between SB-CS, fluorescence, and internal conversion in three related PDI dimers linked at the headland positions with o-, m-, and p-phenylene moieties: o-PDI₂, m-PDI₂, and p-PDI₂, respectively. It is found that o-PDI₂ supports SB-CS yielding PDI^•+-PDI^•-, which is in equilibrium with the o-PDI₂ first excited state in a polar solvent (CH₂Cl₂) while m-PDI₂ and p-PDI₂ exhibit accelerated internal conversion due to the motion of the linker along with subnanosecond intersystem crossing (ISC). Electronic coupling and structural dynamics are shown to play a significant role, with o-PDI₂ being the only member of the series that exhibits significant through-bond interchromophore coupling. The pronounced o-PDI₂ steric congestion prevents the free internal rotation that leads to rapid deactivation of the excited state in the other dimers.

Electrochromic Polycationic Organoboronium Macrocycles with Multiple Redox States

Polycationic macrocycles are attractive as they display unique molecular switching capabilities arising from their redox properties. Although diverse polycationic macrocycles have been developed, those based on cationic boron systems remain very limited. We present herein the development of novel polycationic macrocycles by introducing organoboronium moieties into a conjugated organoboron macrocyclic framework. These macrocycles consist of four bipyridylboronium units that are connected by fluorene and either electron-deficient arylborane or electron-rich arylamine moieties. Electrochemical studies reveal that the macrocycles undergo reversible multi-step redox processes with transfer of up to 10 electrons. Switchable electrochromic behavior is demonstrated via spectroelectrochemical studies and the observed color changes are rationalized by correlation with computed electronic transitions using DFT methods.

Efficient Photoinduced Energy and Electron Transfers in a Tetraphenylethene-Based Octacationic Cage Through Host-Guest Complexation

Artificial photofunctional systems with energy and electron transfer functions, inspired from photosynthesis in nature, have been developed for many promising applications including solar cell, biolabeling, photoelectric materials, and photodriven catalysis. Supramolecular hosts including macrocycles and cages have been explored for simulating photosynthesis based on a host-guest strategy. Herein, we report a host-guest approach by using a tetraphenylethene-based octacationic cage and fluorescent dyes to construct artificial photofunctional systems with energy and electron transfer functions. The cage traps various dyes within its hydrophobic cavity to form 1:1 host-guest complexes via CH-π, π-π, and/or electrostatic interactions in solution. The efficient energy transfer and ultrafast photoinduced electron transfer between the cage and dyes are competitive processes with each other in artificial photofunctional systems. Spectroscopic techniques that confirm energy transfer from the fluorescent cage to dyes (e.g., NiR, R700, and R800) are efficient, which induce the red shift of fluorescence. On the other hand, ultrafast photoinduced electron transfer from dyes (e.g., ICG, AG, and AV) to the fluorescent cage can induce fluorescence quenching. This study provides an insight into the construction of artificial photofunctional systems with energy and electron transfer functions via a host-guest approach in solution.

Supramolecular Porous Organic Nanocomposites for Heterogeneous Photocatalysis of a Sulfur Mustard Simulant

Efficient heterogeneous photosensitizing materials require both large accessible surface areas and excitons of suitable energies and with well-defined spin structures. Confinement of the tetracationic cyclophane (ExBox⁴⁺ ) within a nonporous anionic polystyrene sulfonate (PSS) matrix leads to a surface area increase of up to 225 m² g^-1 in ExBox•PSS. Efficient intersystem crossing is achieved by combining the spin-orbit coupling associated to Br heavy atoms in 1,3,5,8-tetrabromopyrene (TBP), and the photoinduced electron transfer in a TBP⊂ExBox⁴⁺ supramolecular dyad. The TBP⊂ExBox⁴⁺ complex displays a charge transfer band at 450 nm and an exciplex emission at 520 nm, indicating the formation of new mixed-electronic states. The lowest triplet state (T₁ , 1.89 eV) is localized on the TBP and is close in energy with the charge separated state (CT, 2.14 eV). The homogeneous and heterogeneous photocatalytic activities of the TBP⊂ExBox⁴⁺ , for the elimination of a sulfur mustard simulant, has proved to be significantly more efficient than TBP and ExBox⁺⁴ , confirming the importance of the newly formed excited-state manifold in TBP⊂ExBox⁴⁺ for the population of the low-lying T₁ state. The high stability, facile preparation, and high performance of the TBP⊂ExBox•PSS nanocomposites augur well for the future development of new supramolecular heterogeneous photosensitizers using host-guest chemistry.

Viologen Derivatives Extended with Aromatic Rings Acting as Negative Electrode Materials for Use in Rechargeable Molecular Ion Batteries

Many types of batteries have been proposed as next-generation energy-storage systems. One candidate is a rocking-chair-type "molecular ion battery" in which a molecular ion, instead of Li⁺ , works as a charge carrier. Previously, we reported a viologen-type derivative as a negative electrode material that releases and receives PF₆ ^- anions during the charge-discharge process; however, its redox potential was not satisfactorily low. Further, the two potential plateaus of this material (difference=0.5 V) should be reduced. In this study, PF₆ ^- salts of viologen (bipyridinium) derivatives extended by aromatic rings were synthesized to obtain a negative electrode material with a lower redox potential and small potential change during the charge and discharge processes. Some of the synthesized viologen derivatives were fluorescent even in solid-state electrodes. In the half-cell configuration, the prepared negative electrode materials showed average voltages of approximately 2 V (vs. Li⁺ /Li), which is lower than that of conventional viologen derivatives.

Mechanical-Bond-Induced Exciplex Fluorescence in an Anthracene-Based Homo[2]catenane

Collisional intermolecular interactions between excited states form short-lived dimers and complexes that lead to the emergence of excimer/exciplex emission of lower energy, a phenomenon which must be differentiated from the photoluminescence (PL) arising from the monomeric molecules. Although the utilization of noncovalent bonding interactions, leading to the generation of excimer/exciplex PL, has been investigated extensively, precise control of the aggregates and their persistence at very low concentrations remains a rare phenomenon. In the search for a fresh approach, we sought to obtain exciplex PL from permanent structures by incorporating anthracene moieties into pyridinium-containing mechanically interlocked molecules. Beyond the optical properties of the anthracene moieties, their π-extended nature enforces [π···π] stacking that can overcome the Coulombic repulsion between the pyridinium units, affording an efficient synthesis of an octacationic homo[2]catenane. Notably, upon increasing the ionic strength by adding tetrabutylammonium hexafluorophosphate, the catenane yield increases significantly as a result of the decrease in Coulombic repulsions between the pyridinium units. Although the ground-state photophysical properties of the free cyclophane and the catenane are similar and show a charge-transfer band at ∼455 nm, their PL characters are distinct, denoting different excited states. The cyclophane emits at ∼562 nm (quantum yield ϕ_F = 3.6%, emission lifetime τ_s = 3 ns in MeCN), which is characteristic of a disubstituted anthracene-pyridinium linker. By contrast, the catenane displays an exciplex PL at low concentration (10^-8 M) with an emission band centered on 650 nm (ϕ_F = 0.5%, τ_s = 14 ns) in MeCN and at 675 nm in aqueous solution. Live-cell imaging performed in MIAPaCa-2 prostate cancer cells confirmed that the catenane exciplex emission can be detected at micromolar concentrations.

Femtosecond Transient Absorption Microscopy of Singlet Exciton Motion in Side-Chain Engineered Perylene-Diimide Thin Films

We present a statistical analysis of femtosecond transient absorption microscopy applied to four different organic semiconductor thin films based on perylene-diimide (PDI). By achieving a temporal resolution of 12 fs with simultaneous sub-10 nm spatial precision, we directly probe the underlying exciton transport characteristics within 3 ps after photoexcitation free of model assumptions. Our study reveals sub-picosecond coherent exciton transport (12-45 cm2 s-1) followed by a diffusive phase of exciton transport (3-17 cm2 s-1). A comparison between the different films suggests that the exciton transport in the studied materials is intricately linked to their nanoscale morphology, with PDI films that form large crystalline domains exhibiting the largest diffusion coefficients and transport lengths. Our study demonstrates the advantages of directly studying ultrafast transport properties at the nanometer length scale and highlights the need to examine nanoscale morphology when investigating exciton transport in organic as well as inorganic semiconductors.

Tubular Perylene Bisimide Macrocycles for the Recognition of Geometrical Isomers of Azobenzenes

Perylene bisimide-based materials are good candidates for photosensitive applications. Herein, we report synthesis, characterization, and complexation studies of perylene bisimide macrocycles obtained through bayside coupling. The isomeric macrocycles incorporated with interesting optical properties and tubular-shaped cavities are able to recognize geometric isomers of azobenzenes and aromatic amines. Such selective recognition is useful toward developing potential sensors for interesting isomeric pairs in the future.

Structure and luminescence properties of supramolecular polymers of amphiphilic aromatic thioether–peptide conjugates in water

We present the preparation of luminophore–peptide conjugates that self-assemble into phosphorescent supramolecular polymers in neutral buffer.

Novel dithiano-thieno fused perylene diimides: synthesis, characterization and application in organic thin-film transistors (OTFTs)

Novel dithiano-thieno fused perylene diimides are facilely synthesized and investigated in organic thin-film transistor (OTFT) devices for the first time.

Coexistence of distinct intramolecular electron transfer pathways in polyoxometalate based molecular triads

Polyoxometalate (POM)-associated charge-separated states, formed by the photoinduced oxidation of a covalently attached photosensitizer and reduction of the POM, have attracted much attention due to the remarkable catalytic properties of the reduced POMs. However, short lifetimes of the POM-associated charge-separated state, which in some cases lead to the backward electron transfer being more rapid than the formation of the charge-separated state itself, are generally observed. Recently, we reported on the first example of a relative long-lived (τ = 470 ns) charge-separated state in a Ru(ii) bis(terpyridine)-POM molecular dyad. In this manuscript, further studies on extended molecular structures - two molecular triads - which contain an additional electron donor, phenothiazine (PTZ) or π-extended tetrathiafulvalene (exTTF), are discussed. We show that the excitation of the photosensitizer leads to the population of two distinct MLCT states, which differ in the distribution of excess electron density on the two distinct tpy ligands. These two MLCT states decay separately and, thus, constitute the starting points for distinct intramolecular electron-transfer pathways leading to the simultaneous population of two partially charge-separated states, i.e. PTZ˙+-Ru(tpy)2˙--POM and PTZ-RuIII(tpy)2-POM˙-. These independent decay pathways are unaffected by the choice of the electron donor. Thus, the initial charge distribution within the coordination environment of the photocenter determines the nature of the subsequent (partially) charge separated state that is formed in the triads. These results might open new avenues to design molecular interfaces, in which the directionality of electron transfer can be tuned by the choice of initial excitation.

Multichromophoric hybrid species made of perylene bisimide derivatives and Ru(ii) and Os(ii) polypyridine subunits

Herein, the synthesis and the photophysical and redox properties of a new perylene bisimide (PBI) species (L), bearing two 1,10-phenanthroline (phen) ligands at the two imide positions of the PBI, and its dinuclear Ru(ii) and Os(ii) complexes, [(bpy)₂Ru(μ-L)Ru(bpy)₂](PF₆)₄ (Ru2; bpy = 2,2'-bipyridine) and [(Me₂-bpy)₂Os(μ-L)Os(Me₂-bpy)₂](PF₆)₄ (Os2; Me₂-bpy = (4,4'-dimethyl)-2,2'-bipyridine), are reported. The absorption spectra of the compounds are dominated by the structured bands of the PBI subunit due to the lowest-energy spin-allowed π-π* transition. The spin-allowed MLCT transitions in Ru2 and Os2 are inferred by the absorption at 350-470 nm, where the PBI absorption is negligible. The absorption band extends towards the red region for Os2 due to the spin-forbidden MLCT transitions, intensified by the heavy osmium center. The reduction processes of the compounds are dominated by two successive mono-electronic PBI-based processes, which in the metal complexes are slightly shifted compared to the free ligand. On oxidation, both metal complexes undergo an apparent bi-electronic process (at 1.31 V vs. SCE for Ru2 and 0.77 V for Os2), attributed to the simultaneous one-electron oxidation of the two weakly-interacting metal centers. In Ru2 and Os2, the intense fluorescence of L subunit (λ_max, 535 nm; τ, 4.3 ns; Φ, 0.91) is fully quenched, mainly by photoinduced electron transfer from the metal centers, on the ps timescale (time constant, 11 ps in Ru2 and 3 ps in Os2). Such photoinduced electron transfer leads to the formation of a charge-separated state, which directly decays to the ground state in about 70 ps in Os2, but produces the triplet π-π* state of the PBI subunit in 35 ps in Ru2. The results provide information on the excited-state processes of the hybrid species combining two dominant classes of chromophore/luminophore species, the PBI and the metal polypyridine complexes, and can be used for future design on new hybrid species with made-to-order properties.

Controllable Fluorescence Switching of a Coordination Chain Based on the Photoinduced Single-Crystal-to-Single-Crystal Reversible Transformation of a syn-[2.2]Metacyclophane

The observation of a reversible chemical transformation corresponding to an external stimulus in the solid state is intriguing in the exploration of smart materials, which can potentially be applied in molecular machines, molecular switches, sensors, and data storage devices. The solid-state photodimerization reaction of 1,3-bis[2-(4-pyridyl)ethenyl]benzene (1,3-bpeb) in a one-dimensional coordination polymer {[Cd₂(1,3-bpeb)₂(4-FBA)₄]·H₂O}_n (4-FBA = 4-fluorobenzoate) with 365 nm UV light afforded syn-tetrakis(4-pyridyl)-1,2,9,10-diethano[2.2]metacyclophane (syn-tpmcp) in quantitative yield via a single-crystal-to-single-crystal (SCSC) transformation. Upon irradiation with 254 nm UV light, an SCSC conversion from syn-tpmcp to 1,3-bpeb was also achieved in quantitative yield within the syn-tpmcp-supported coordination polymer {[Cd₂(syn-tpmcp)(4-FBA)₄]·H₂O}_n. In particular, accompanied by the reversible transformation between 1,3-bpeb and syn-tpmcp, the coordination chain exhibits photocontrollable fluorescence-switching behavior, which makes this intelligent material an appealing candidate for practical applications.

Influence of imide-substituents on the H-type aggregates of perylene diimides bearing cetyloxy side-chains at bay positions

A series of perylene-3,4:9,10-tetracarboxylic acid diimides (PDIs, namely TYR-PDI, AEP-PDI, CET-PDI, ANP-PDI and KOD-PDI), comprising long linear cetyloxy side-chains functionalized at the 1,7-bay positions and the different substituents (i.e., hydrophobic/hydrophilic segments) symmetrically linked at the two imide-positions of the perylene core were synthesized to investigate the influence of imide-substituent patterns on the aggregation behaviours of PDIs. The photophysical properties of these PDIs were studied by UV-Vis absorption, fluorescence and time-resolved photoluminescence spectroscopy. The differences in the photophysical properties of the PDIs indicate (i) blue-shifted and broadening absorption properties in both solution and thin-films, (ii) red-shifted and broadening fluorescence behavior at their emission maximum in solution, however, blue-shifted fluorescence behavior in thin-films, and (iii) obviously longer fluorescence life-times corresponding to the existence of rotationally displaced H-type aggregates. The formation of short-range ordered rod-like microstructures through face-to-face alignment of columnar rectangular H-type PDI aggregates was rationalized by scanning electron microscopy. The X-ray diffraction study revealed that the formation of well-defined columnar rectangular (Col_rp) H-type PDI aggregates indicated a nearly constant intracolumnar stacking distance of ∼3.9 Å for all PDIs. All of these findings were consistent with the formation of hydrophobic/hydrophilic interactions between the imide-substituents in addition to the strong hydrophobic π-π stacking interactions between the conjugated perylene cores, which were enforced in the H-type PDI aggregates that spontaneously self-organized into Col_rp structures.

In situ polymerization of supramolecular nanorods assembled from polymerizable perylene bisimide

Dimethacryl amide functionalized perylene bisimide monomer was synthesized, in-situ free radical polymerization was then performed in the organized state to maintain the assembly structures.

Two-Component Fluorescent-Semiconducting Hydrogel from Naphthalene Diimide-Appended Peptide with Long-Chain Amines: Variation in Thermal and Mechanical Strengths of Gels

Two-component fluorescent hydrogels have been discovered, containing the mixtures of naphthalene diimide (NDI)-conjugated peptide-functionalized bola-amphiphile and primary amines with long alkyl chains at physiological pH 7.46. The aggregation-induced enhanced emission associated with an NDI-appended peptide in aqueous medium is rare, as water is known to be a good quencher of fluorescence. In this study, an NDI-containing gelator peptide forms a highly fluorescent aggregate in aqueous medium. Absorption and emission spectroscopic techniques reveal the formation of J-aggregates among the chromophoric moieties in their aggregated state in aqueous medium. However, this NDI-containing peptide does not form any gel in aqueous medium. In the presence of the primary amines with long alkyl chains in the buffer solution, it forms two-component fluorescent hydrogels exhibiting bright yellow fluorescence under a UV lamp (365 nm). Probably, the acid-amine interaction between the amines and the bola-amphiphile triggers the gel formation, as evident from Fourier transform infrared data, indicating the presence of a carboxylate group (-COO^-) and an ammonium species (NH₃⁺) in the coassembled two-component gel system. Low- and wide-angle powder X-ray diffraction and small-angle X-ray scattering further support the fact that the coassembled state in the gel form is produced by the supramolecular interaction between the NDI-based bola-amphiphile and the long-chain amines. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy images reveal that the π-conjugated coassembled hydrogels exhibit nanofibrillar network morphologies. Interestingly, the coassembled hydrogels exhibit an enhanced fluorescence emission, excited-state lifetime, and quantum yield when compared with those of the NDI-containing amphiphile alone in its self-assembled state in aqueous medium. Moreover, the thermal stability and mechanical strength of these gels have been successfully tuned by varying the alkyl chain length of the corresponding amine. Moreover, these NDI-peptide-conjugated soft materials exhibit semiconducting behavior in their respective coassembled states. This holds future promise to use these peptide-appended NDI-based coassembled soft materials for applications in optoelectronic and other devices.

Broad-Spectrum Tunable Photoluminescent Nanomaterials Constructed from a Modular Light-Harvesting Platform Based on Macrocyclic Amphiphiles

Broad-spectrum tunable photoluminescent nanomaterials are developed based on macrocyclic amphiphiles serving as a novel modular light-harvesting platform with discrete addressability of luminophores in a noncovalent way. By simply varying the donor/acceptor ratio, a broad spectrum of energy transfer outputs is achieved, pointing toward a proof-of-principle application as fluorescent inks for security printing.

Ultrafast Two-Electron Transfer in a CdS Quantum Dot-Extended-Viologen Cyclophane Complex

Time-resolved optical spectroscopies reveal multielectron transfer from the biexcitonic state of a CdS quantum dot to an adsorbed tetracationic compound cyclobis(4,4'-(1,4-phenylene) bipyridin-1-ium-1,4-phenylene-bis(methylene)) (ExBox(4+)) to form both the ExBox(3+•) and the doubly reduced ExBox(2(+•)) states from a single laser pulse. Electron transfer in the single-exciton regime occurs in 1 ps. At higher excitation powers the second electron transfer takes ∼5 ps, which leads to a mixture of redox states of the acceptor ligand. The doubly reduced ExBox(2(+•)) state has a lifetime of ∼10 ns, while CdS(+•):ExBox(3+•) recombines with multiple time constants, the longest of which is ∼300 μs. The long-lived charge separation and ability to accumulate multiple charges on ExBox(4+) demonstrate the potential of the CdS:ExBox(4+) complex to serve as a platform for two-electron photocatalysis.