Cyclic Triimidazole Derivatives: Intriguing Examples of Multiple Emissions and Ultralong Phosphorescence at Room Temperature

The performance of solid luminogens depends on both their inherent electronic properties and their packing status. Intermolecular interactions have been exploited to achieve persistent room‐temperature phosphorescence (RTP) from organic molecules. However, the design of organic materials with bright RTP and the rationalization of the role of interchromophoric electronic coupling remain challenging tasks. Cyclic triimidazole has been shown to be a promising scaffold for such purposes owing to its crystallization‐induced room‐temperature ultralong phosphorescence (RTUP), which has been associated with H‐aggregation. Herein, we report three triimidazole derivatives as significant examples of multifaceted emission. In particular, dual fluorescence, RTUP, and phosphorescence from the molecular and supramolecular units were observed. H‐aggregation is responsible for the red RTUP, and Br substituents favor yellow molecular phosphorescence while halogen‐bonded Br⋅⋅⋅Br tetrameric units are involved in the blue‐green phosphorescence.     

Monomer and Excimer Emission in a Conformational and Stacking-Adaptable Molecular System

A design strategy that combines molecular conformation, alkyl chain length, and charge-transfer effects has been developed to obtain conformational and stacking-adaptable donor-acceptor-π type molecules for precisely regulating the monomer and excimer emission in a single luminous platform under different environments. These fluorophores can exhibit bright monomer emissions when they are in the dispersed state based on their planar conformation. However, when the luminous molecules with short alkyl side chains are in the crystalline state, their molecular conformation can become distorted, further inducing strong intermolecular interactions and staggered π-π stacking for bright excimer emission. More importantly, their dispersed and aggregated states can be reversibly regulated in a phase-change fatty acid matrix, to achieve temperature-responsive fluorescence for temperature monitoring and advanced information encryption.     

Luminescence Color Tuning from Blue to Near Infrared of Stable Luminescent Solid Materials Based on Bis‐o‐Carborane‐Substituted Oligoacenes

Aryl‐substituted o ‐carboranes have shown highly efficient solid‐state emission in previous studies. To demonstrate color tuning of the solid‐state emission in an aryl‐o ‐carborane‐based system, bis‐o ‐carborane‐substituted oligoacenes were synthesized and their properties were systematically investigated. Optical and electrochemical measurements revealed efficient decreases in energy band gaps and lowest unoccupied molecular orbital (LUMO) levels by adding a number of fused benzene rings for the extension of π‐conjugation. As a consequence, bright solid‐state emission was observed in the region from blue to near infrared (NIR). Furthermore, various useful features were obtained from the modified o ‐carboranes as an optical material. The naphthalene derivatives exhibited aggregation‐induced emission (AIE) and almost 100 % quantum efficiency in the crystalline state. Furthermore, it was shown that the tetracene derivative with NIR‐emissive properties had high durability toward photo‐bleaching under UV irradiation.     

Pyrene-fluorene hybrids containing acetylene linkage as color-tunable emitting materials for organic light-emitting diodes

New blue- to yellow-emitting materials have been developed by incorporating fluorene-based chromophores on pyrene core with acetylene linkage and using multifold palladium-catalyzed cross-coupling reactions. Both mono- and tetrasubstituted derivatives have been synthesized and characterized. The tetrasubstituted derivatives displayed red-shifted emission when compared to the monosubstituted derivative indicative of an extended conjugation in the former. End-capping with a diphenylamine unit further red-shifted the absorption and emission profiles and imparted a weak dipolar character to the molecules. Amine-containing derivatives displayed positive solvatochromism in the fluorescence spectra indicating a more polar excited state due to an efficient charge migration from the diphenylamine donor to the pyrene π-acceptor. All of the derivatives were tested as emitting dopants with host material 4,4'-bis(9H-carbazol-9-yl)biphenyl (CBP) in a multilayered OLED and found to exhibit bright blue or yellow electroluminescence. The device utilizing 1,3,6,8-tetrasubstituted pyrene derivative as a dopant emitter displayed highest maximum luminescence 4630 cd/m(2) with power efficiency 3.8 lm/W and current efficiency 7.1 cd/A at 100 cd/m(2) attributable to the proper alignment of energy levels that led to the efficient harvesting of excitons. All of the devices exhibited color purity over a wide range of operating voltages.     

Novel carbazole-based organogels modulated by tert-butyl moieties

tert-Butyl groups can modulate the self-assembling properties of carbazole derivatives; organogel fibers with a bright blue emission are generated, directed by the cooperation of hydrogen bonding as well as pi-pi interactions.     

Large Two‐Photon Absorption of Terpyridine‐Based Quadrupolar Derivatives: Towards their Applications in Optical Limiting and Biological Imaging

Developing organic chromophores with large two‐photon absorption (TPA) in both organic solvents and aqueous media is crucial owing to their applications in solid‐state photonic devices and biological imaging. Herein, a series of novel terpyridine‐based quadrupolar derivatives have been synthesized. The influences of electron‐donating group, type of conjugated bridge, as well as solvent polarity on the molecular TPA properties have been investigated in detail. In contrast to the case in organic solvents, bis(thienyl)‐benzothiadiazole as a rigid conjugated bridge will completely quench molecular two‐photon emission in aqueous media. However, the combination of alkylcarbazole as the donor and bis(styryl)benzene as a conjugation bridge can enlarge molecular TPA cross‐sections in both organic solvent and aqueous media. The reasonable two‐photon emission brightness for the organic nanoparticles of chromophores 3 – 5 in the aqueous media, prepared by the reprecipitation method, enables them to be used as probes for in vivo biological imaging.     

Spectroscopic study of molecular associations between FMN and β-carbolines

The spectrophotometric and thermodynamic properties of molecular complexes of flavin mononucleotide (FMN) (riboflavin 5′-phosphate) with some β-carboline derivatives have been investigated in aqueous solution. The molecular associations have been examined by means of electronic absorption spectra, since in each a new charge-transfer band has been located, and also the variation of the fluorescence emission of FMN on the solutions has been observed. The formation constants for the molecular complexes were determined from absorption data using the Foster—Hammick—Wardley method. The quenching phenomenon observed in FMN fluorescence is related to the concentration of the β-carboline derivatives, allowing the calculation of the quenching constants for FMN-β-carboline complexes. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the β-carboline molecule on the stability of the complexes formed was also investigated.     

Copper(I) complexes with bipyridyl and phosphine ligands: a systematic study

Phosphorescent copper(I) complexes carrying 2,2'-bipyridyl derivatives and phosphine ligands have been prepared and fully characterised. The role of the bipyridyl as well as the phosphine ligands in defining the optical, as well as the chemical properties of the complexes, are discussed. The light emission of these complexes is investigated as a function of the molecular geometry: rigid complexes with restricted freedom to rearrange in the excited state are found to show a quantum yield of phosphorescence one order of magnitude higher than those complexes with no steric constraint. The complexes have been extruded in a polymer matrix as a proof of principle of their processability.     

Crystallization‐Induced Emission of Azobenzene Derivatives

Most azobenzene derivatives are utilized as well‐defined photoresponsive materials, but their emission properties have not been of great interest as they are relatively poor. Here, we report crystallization‐induced emission (CIE) based on the suppression of the photoisomerization of azobenzene derivatives. Although these molecules show negligible emission in solution, their microcrystals exhibit intense emission from the azobenzene moieties as a result of CIE. Upon rapid precipitation, fine particles with low crystallinity were kinetically formed and underwent CIE over time with a concomitant increase in crystallinity. Furthermore, we demonstrated “photocutting” of an emissive single crystal using a strong laser by a combination of CIE behavior and photomelting based on the photoisomerization of the azobenzene moiety. Our results regarding the CIE behavior of azobenzene derivatives in addition to their photoisomerization can provide a new platform for developing photoresponsive luminescent materials.     

Evaluation of a simple and novel fluorescent anion sensor, 4-quinolone, and modification of the emission color by substitutions based on molecular orbital calculations

4-Quinolone (4-QO) was evaluated as a simple and novel fluorescent anion sensor, and the modification of its emission color was carried out. The series of 4-QO derivatives having molecular orbitals with different energy levels was designed by substitutions at the 6 and 7 positions based on the molecular orbital calculations. All derivatives showed drastic fluorescence enhancements in the presence of F⁻ via the intramolecular charge transfer mechanism, and the successful modification of the emission color was achieved. The anion-induced emission colors of these derivatives as well as their binding affinities for F⁻ could be predicted by ab initio quantum chemical calculations, indicating that the present calculations are useful in designing new anion sensors.     

多功能二噻吩乙烯光致变色光分子开关材料

光致变色材料是一类在不同波长的光交替照射下,产生两种可进行可逆转换的光致异构体并伴随明显的光物理和光化学性能变化的材料。基于其特殊的光致异构性质,人们已开发出多种光致变色功能材料并将其广泛应用于超高密度光信息存储、分子开关、分子逻辑门、分子导线、光电材料、多光子器件、表面/纳米器件、液晶材料、化学传感、生物成像、自组装、聚集诱导发光、光控生物体系等诸多领域。其中,二噻吩乙烯类化合物因其出色的热稳定性、优良的耐疲劳性、快的响应速率、高的转化率和量子产率以及出色的固相反应活性而成为理想的光致变色材料之一。本文主要围绕近期本研究组研究成果着重介绍近几年二噻吩乙烯类化合物从溶液体系到功能化表面体系的研究进展,探讨当前该领域存在的问题并对其前景和发展方向进行展望。     

Spectroscopic study of molecular associations between flavins FAD and RFN and some indole derivatives

The formation of complexes between two flavins [flavine adenine dinucleotide (FAD) and riboflavin (RFN)] and some indole derivatives has been studied in aqueous solution. The molecular associations have been examined by means of electronic absorption spectra, since in each, a new charge-transfer like band has been located, and also by observing the variation of the fluorescence emission of FAD or RFN on the solutions. The formation constants for the molecular complexes were determined from data of absorption using the Foster—Hammick—Wardley method. The quenching fluorescence phenomena observed for the FAD and RFN were related to the concentration of the indole derivatives and the corresponding quenching constants have been determined. Thermodynamic parameters have been derived from the values of association constants for the molecular complexes at several temperatures. Clear evidence is found for the influence on the stability of these complexes of the different substituent groups in the indole derivatives and the molecular structure of both flavins.     

Synthesis and Photoproperties of Silicon Phthalocyanines and Silicon Naphthalocyanines

Silicon phthalocyanines and silicon naphthalocyanines, which are two derivatives in the family of hematoporphyrin, have been synthesized to assess their potential as photosensitizers for photodynamic therapy. For these complexes the red shift of their Q-band maximum absorption tends to depend on the nature of the axial substituent. The bimolecular rate coefficients for the interacting between photosensitizer, either SiNC or SiPC, and generated singlet molecular oxygen were determined from the time-resolved emission spectrum of singlet oxygen at 1.27 μm. On the basis of these data the electron-transfer quenching mechanism is discussed in relation to the Marcus model.     

Photochemical behaviour upon the inclusion for some volatile organic compounds in new fluorescent indolizine β-cyclodextrin sensors

The potentialities of three new fluorescent indolizine modified β-cyclodextrin have been investigated as molecular chemosensors. The pyridin-4-ylindolizine β-cyclodextrin derivatives were synthesised by an amidation between the fluorescent indolizine derivatives and 6-deoxy-6-amino-β-cyclodextrin. The multiconformational search by MM3 and AM1 method in gaseous state and in water respectively suggest the “open cavity” structure as the most probable. These compounds have been characterised spectroscopically by their emission spectra and their sensing ability towards 1-adamantanol, phenol and p-cresol. The fluorescent properties and sensitivity factor of the sensor containing an indolizine product with a perfluored aromatic fragment recommended it fairly as sensor for the detection of volatile organic compounds (VOCs), while the other two sensors, with an aliphatic fragment, can be utilised as biological markers. Finally, a significant bathochromic shift is observed for the sensor containing a t-butyl fragment, in such a way that this sensor may also lead to the detection of VOCs.     

Crystallization-induced light-emission enhancement of diphenylmethane derivatives

A family of diphenylmethane derivatives has been synthesized and their luminescence properties characterized. While in solution the compounds are weakly emissive, showing no aggregation-induced emission enhancement, the crystals of three dialkyl 5,5′-methylenebis(2-hydroxybenzoate) samples exhibit intense emission. This emission enhancement upon crystallization is ascribed to particular molecular packing, which stiffens the structure of the compounds via hydrogen bonds, preventing consecutive π–π interactions.     

An acenaphthopyrrolone-dipicolylamine derivative as a selective and sensitive chemosensor for group IIB cations

The recently reported acenaphthopyrrolone (ACNP) class of fluorophores have remarkably bright emission in the red end of the visible spectrum. We demonstrated that straightforward derivatization with 2-aminoethyl-dipicolylamine yields a selective and sensitive chemosensor for Zn(II), Cd(II) and Hg(II) ions. Further modifications could result in water-soluble derivatives, with practical applications in intracellular imaging of Zn(II) concentrations.     

Intermolecular electronic coupling of 9-methyl-9H-dibenzo [a,c] carbazole for strong emission in aggregated state by substituent effect

Bright emission of organic luminogens at aggregated state has attracted increasing attention for their potential applications in opto-electronic devices and bio-/chemo-sensors. In this article, upon the introduction of different substituents(Br, Ph and TPh) to the large conjugated core of 9-methyl-9H-dibenzo[a,c]carbazole(DBC) moiety, the resultant luminogens demonstrated PL quantum yields in solid state ranging from 4.81% to 47.39%. Through the systematic investigation of molecular packing,together with theory calculation, the strong intermolecular electronic coupling in the dimers is proved as the main factor to the bright emission in the solid state. The results afforded a new avenue to investigate the intrinsic relationship among the molecular structures, packing modes and emission properties.     

用于生物成像的三线态-三线态湮灭上转换发光纳米胶囊

为解决三线态-三线态湮灭上转换发光材料(TTA-UC)生物应用时固载化困难的问题,通过一步细乳液聚合法合成了以正十六烷为内核,以红光激发的硅酞菁为敏化剂和发光高效的红荧烯为受体,具有优异上转换发光性能的核壳结构纳米胶囊(TTA-UCNP)。TTA-UCNP粒径约为190 nm,均一性及分散性良好。体系引入了抗氧化剂D-柠檬烯和聚异丁烯,有效消除了氧气分子对上转换发光过程的淬灭,保证了上转换发光的稳定性。在动物成像应用中,TTA-UCNP成功实现了活体层次前哨淋巴结高信噪比的成像及长时间示踪。     

双(三氯甲基)三嗪类化合物光生酸反应的研究

对 3种具不同结构 (三氯甲基 )三嗪化合物的光致生酸及光敏化生酸问题进行了研究 .从其吸收光谱、荧光光谱、荧光猝灭以及光致生酸过程的测定结果表明 ,三嗪化合物的敏化光致生酸具有电子转移性质 .发现在三嗪化合物分子中存在着归属于核的局域发光以及分子内的电荷转移发光两个部分 .局域的激发与发光和化合物光致生酸有着密切的关系 ,而电荷转移发光则会增强或扩充化合物的吸收和发射光谱范围 ,在光致生酸中也有重要的作用 .一种完美的光致生酸化合物分子的设计和合成必须对上述两个方面均加以注意 ,使能达到互补和协同的作用     

State-crossing from a Locally Excited to an Electron Transfer State(SLEET) Model Rationalizing the Aggregation-induced Emission Mechanism of (Bi)piperidylanthracenes

Luminogens with aggregation-induced emission(AIE)characteristics(or AIEgens)have been widely used in various applications due to their excellent luminescent properties in molecular aggregates and the solid state.A deep understanding of the AIE mechanism is critical for the rational development of AIEgens.In this work,the“state-crossing from a locally excited to an electron transfer state”(SLEET)model is employed to rationalize the AIE phenomenon of two(bi)piperidylanthracenes.According to the SLEET model,an electron transfer(ET)state is formed along with the rotation of the piperidyl group in the excited state of(bi)piperidylan-thracene monomers,leading to fluorescence quenching.In contrast,a bright state exists in the crystal and molecular aggregates of these compounds,as the intermolecular interactions restrict the formation of the dark ET state.This mechanistic understanding could inspire the deployment of the SLEET model in the rational designs of various functional AIEgens.