Protein‐like Enwrapped Perylene Bisimide Chromophore as a Bright Microcrystalline Emitter Material

Strongly emissive solid‐state materials are mandatory components for many emerging optoelectronic technologies, but fluorescence is often quenched in the solid state owing to strong intermolecular interactions. The design of new organic pigments, which retain their optical properties despite their high tendency to crystallize, could overcome such limitations. Herein, we show a new material with monomer‐like absorption and emission profiles as well as fluorescence quantum yields over 90 % in its crystalline solid state. The material was synthesized by attaching two bulky tris(4‐tert‐butylphenyl)phenoxy substituents at the perylene bisimide bay positions. These substituents direct a packing arrangement with full enwrapping of the chromophore and unidirectional chromophore alignment within the crystal lattice to afford optical properties that resemble those of their natural pigment counterparts, in which chromophores are rigidly embedded in protein environments.     

Molecular Packing and Solid-State Photophysical Properties of 1,3,6,8-Tetraalkylpyrenes

The relationship between the photophysical properties and molecular orientation of 1,3,6,8-tetraalkylpyrenes in the solid state is described herein. The introduction of alkyl groups with different chain structures (in terms of length and branching) did not affect the photophysical properties in solution, but significantly shifted the emission wavelengths and fluorescence quantum yields in the solid state for some samples. Pyrenes bearing ethyl, isobutyl, or neopentyl groups at the 1-, 3-, 6-, and 8-positions showed similar emission profiles in both the solution and solid states. In contrast, pyrenes bearing other alkyl groups exhibited an excimer emission in the solid state, similar to that of the parent pyrene. On studying the photophysical properties in the solid state with respect to the obtained crystal structures, the observed solid-state photophysical properties were found to depend on the relative position of the pyrene chromophores. The solid-state photophysical properties can be controlled by the alkyl groups, which provide changing crystal packing. Among the pyrenes tested, 1,3,6,8-tetraethylpyrene showed the highest fluorescence quantum yield of 0.88 in the solid state.     

Highly Deep-Blue Luminescent Twisted Diphenylamino Terphenyl Emitters by Bromine-Lithium Exchange Borylation-Suzuki Sequence

Four novel intensively blue luminescent chromophores were readily synthesized by bromine-lithium exchange borylation-Suzuki (BLEBS) sequence in moderate to good yields. Their electronic properties were studied by absorption and emission spectroscopy and quantum chemical calculations revealing deep-blue emission in solution as well as in the solid state and upon embedding into a PMMA (polymethylmethacrylate) matrix with small FWHM (full width at half maximum) values and CIE y values smaller than 0.1. Moreover, high photoluminescence quantum yields (PLQY), partially close to unity, are found.     

Enhanced Solution and Solid-State Emission and Tunable White-Light Emission Harvested by Supramolecular Approaches

Organic luminescent materials with high quantum yields and/or white-light-emitting properties in particular play a crucial role in labeling and optoelectronic devices. In this work we have synthesized a new 2,3,6,7-tetramethoxy-9,10-di-p-tolylanthracene-bridged pillar[5]arene dimer with persistent mazarine blue fluorescent emission and much higher quantum yields in both solution and the solid state in comparison with its corresponding emissive linker without pillarene units, which exhibits typical aggregation-caused quenching. According to the fluorescence data and single-crystal analyses, their contrasting fluorescent performances can be rationally ascribed to their different stacking structures and intermolecular interactions. Three fluorescent guests containing different chromophores and/or terminal binding sites have also been synthesized to interact with the pillar[5]arene dimer to construct supramolecular ensembles with highly controllable luminescence, taking advantage of the stimuli-responsive properties of the supramolecular host–guest interactions. Intriguingly, multicolor fluorescence, including white-light emission (0.31, 0.35), which is in high demand, has been achieved by tuning the molar ratio of the host and guest and/or by changing the solvent system. This strategy holds great potential for the design and development of fluorescent materials with high quantum yields, controllable emission wavelength, and good stimuli-responsiveness.     

Tuning the Solid‐State Luminescence of BODIPY Derivatives with Bulky Arylsilyl Groups: Synthesis and Spectroscopic Properties

Boron dipyrromethenes (BODIPYs) with bulky triphenylsilylphenyl(ethynyl) and triphenylsilylphenyl substituents on pyrrole sites were prepared via Hagihara–Sonogashira and Suzuki–Miyaura cross‐coupling with ethynyl‐terminated tetraphenylsilane and boronic acid‐terminated tetraphenylsilane. The chromophores are designed to prevent intermolecular π–π stacking interaction and enhance fluorescence in the solid state. Single crystals of 1 a and 2 b for X‐ray structural analysis were obtained, and weak π–π stacking interactions of the neighboring BODIPY molecules were observed. Spectroscopic properties of all of the dyes in various solvents and in films were investigated. Triphenylsilylphenyl‐substituted BODIPYs generally show more pronounced increases in solid‐state emission than triphenylsilylphenyl(ethynyl)‐substituted BODIPYs. Although the simple BODIPYs do not exhibit any fluorescence in the solid state (Φ=0), arylsilyl‐substituted BODIPYs exhibit weak to moderate solid‐state fluorescence with quantum yields of 0.03, 0.07, 0.10, and 0.25. The structure–property relationships were analyzed on the basis of X‐ray crystallography, optical spectroscopy, cyclic voltammetry, and theoretical calculations.     

Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals

Thermotropic ionic liquid crystals based on the flavylium scaffold have been synthesized and studied for their structure-properties relationship for the first time. The mesogens were probed by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Low numbers of alkoxy side chains resulted in smectic (SmA) and lamello-columnar (Lam_Col) phases, whereas higher substituted flavylium salts showed Col_ro as well as ordered and disordered columnar (Col_ho, Col_hd) mesophases. Mesophase width ranged from 13 K to 220 K, giving access to room temperature liquid crystals. The optical properties of the synthesized compounds were probed towards absorption and emission properties. Strong absorption with maxima between 444 and 507 nm was observed, and some chromophores were highly emissive with quantum yields up to 99 %. Ultimately, mesogenic and dye properties were examined by temperature-dependent emissive experiments in the solid state.     

IR-Luminescent Molecules in Hybrid Materials

In the present work we report on steady-state and dynamical optical properties of four polymethine dye molecules absorbing in the near infrared (IR) region (0.8–1.1 m) and emitting around 1.2 m. The molecules are embedded in organically modified silicate (ORMOSIL) material synthesized by a sol-gel method. The investigated samples were prepared as films, deposited on glass substrates. Steady-state absorption and emission measurements have been accomplished for the chromophores in solution as well as in hybrid organic/inorganic films in order to determine the effect of the solid cage on the optical properties of the chromophore. To better understand the influence of the solid network, we also measured for some of the investigated molecules emission transients with femtosecond time resolution. An estimation of the emission quantum yield of the IR dye molecules in a glassy matrix is also given. The kinetic results are sensitive to guest-host interactions.     

Tuning the solid-state luminescence of BODIPY derivatives with bulky arylsilyl groups: synthesis and spectroscopic properties

Boron dipyrromethenes (BODIPYs) with bulky triphenylsilylphenyl(ethynyl) and triphenylsilylphenyl substituents on pyrrole sites were prepared via Hagihara-Sonogashira and Suzuki-Miyaura cross-coupling with ethynyl-terminated tetraphenylsilane and boronic acid-terminated tetraphenylsilane. The chromophores are designed to prevent intermolecular π-π stacking interaction and enhance fluorescence in the solid state. Single crystals of 1?a and 2?b for X-ray structural analysis were obtained, and weak π-π stacking interactions of the neighboring BODIPY molecules were observed. Spectroscopic properties of all of the dyes in various solvents and in films were investigated. Triphenylsilylphenyl-substituted BODIPYs generally show more pronounced increases in solid-state emission than triphenylsilylphenyl(ethynyl)-substituted BODIPYs. Although the simple BODIPYs do not exhibit any fluorescence in the solid state (Φ=0), arylsilyl-substituted BODIPYs exhibit weak to moderate solid-state fluorescence with quantum yields of 0.03, 0.07, 0.10, and 0.25. The structure-property relationships were analyzed on the basis of X-ray crystallography, optical spectroscopy, cyclic voltammetry, and theoretical calculations.     

Theoretical and Experimental Study on Boron β‐Diketonate Complexes with Intense Two‐Photon‐Induced Fluorescence in Solution and in the Solid State

Three boron diketonate chromophores with extended π‐conjugated backbone were prepared and their spectroscopic features were investigated through a combined theoretical/experimental study. It was shown that these complexes, which undergo very large electronic reorganization upon photoexcitation, combine large two‐photon absorption cross section with an emission energy and quantum efficiency in solution that is strongly dependent on solvent polarity. The strong positive influence of boron complexation on the magnitude of the two‐photon absorption was clearly established, and it was shown that the two‐photon absorption properties were dominated by the quadrupolar term. For one of the synthesized compounds, intense one‐ and two‐photon‐induced solid‐state emission (fluorescence quantum yield of 0.65 with maximum wavelength of 610 nm) was obtained as a result of antiparallel J‐aggregate crystal packing.     

Fluorescence Emission of Self-assembling Amyloid-like Peptides: Solution versus Solid State

Analysis of the intrinsic UV-visible fluorescence exhibited by self-assembling amyloid-like peptides in solution and in solid the state highlights that their physical state has a profound impact on the optical properties. In the solid state, a linear dependence of the fluorescence emission peaks as a function of excitation wavelength is detected. On the contrary, an excitation-independent emission is observed in solution. The present findings constitute a valuable benchmark for current and future explanations of the fluorescence emission by amyloids.     

Tuning the Solid‐State Optical Properties of Tetracene Derivatives by Modification of the Alkyl Side‐Chains: Crystallochromy and the Highest Fluorescence Quantum Yield in Acenes Larger than Anthracene

In the solution state, there were no notable differences between the optical properties of a range of alkyl‐substituted tetracenes. However, in the solid state, their photophysical properties changed with respect to the length, shape, number, and substitution pattern of the alkyl side chains, as well as the distribution of two regioisomers. Remarkably, in the solid state, 1,4,7,10‐tetraisopropyltetracene exhibited the highest reported fluorescence quantum yield of any tetracene derivative (0.90). The changes in the optical characteristics of these tetracenes according to the arrangement of the tetracene rings and the color‐change mechanism in the solid state are discussed. Moreover, the world record in solid‐state fluorescence efficiency in acenes larger than anthracene is described. DOI 10.1002/tcr.201200003     

Ultralarge hyperpolarizability twisted pi-electron system electro-optic chromophores: synthesis, solid-state and solution-phase structural characteristics, electronic structures, linear and nonlinear optical properties, and computational studies

This contribution details the synthesis and chemical/physical characterization of a series of unconventional twisted pi-electron system electro-optic (EO) chromophores. Crystallographic analysis of these chromophores reveals large ring-ring dihedral twist angles (80-89 degrees) and a highly charge-separated zwitterionic structure dominating the ground state. NOE NMR measurements of the twist angle in solution confirm that the solid-state twisting persists essentially unchanged in solution. Optical, IR, and NMR spectroscopic studies in both the solution phase and solid state further substantiate that the solid-state structural characteristics persist in solution. The aggregation of these highly polar zwitterions is investigated using several experimental techniques, including concentration-dependent optical and fluorescence spectroscopy and pulsed field gradient spin-echo (PGSE) NMR spectroscopy in combination with solid-state data. These studies reveal clear evidence of the formation of centrosymmetric aggregates in concentrated solutions and in the solid state and provide quantitative information on the extent of aggregation. Solution-phase DC electric-field-induced second-harmonic generation (EFISH) measurements reveal unprecedented hyperpolarizabilities (nonresonant mubeta as high as -488,000 x 10(-48) esu at 1907 nm). Incorporation of these chromophores into guest-host poled polyvinylphenol films provides very large electro-optic coefficients (r(33)) of approximately 330 pm/V at 1310 nm. The aggregation and structure-property effects on the observed linear/nonlinear optical properties are discussed. High-level computations based on state-averaged complete active space self-consistent field (SA-CASSCF) methods provide a new rationale for these exceptional hyperpolarizabilities and demonstrate significant solvation effects on hyperpolarizabilities, in good agreement with experiment. As such, this work suggests new paradigms for molecular hyperpolarizabilities and electro-optics.     

多芳基吡咯衍生物的发光性质及其应用

荧光分子在良溶剂中基本不发光或发光较弱,而在聚集状态下发光较强的现象,称为聚集诱导发光(Aggregation-induced emission,AIE)现象,这与传统的聚集导致猝灭(Aggregation-caused quenching,ACQ)现象相反。本文研究了多苯基吡咯衍生物的结构与发光性能的关系。通过比较吡咯衍生物的单晶结构和发光性质发现扭曲的结构可以限制共轭发光基团的分子内旋转(RIR),这是产生AIE现象的主要原因。羧酸化的吡咯衍生物可以对Al³⁺实时、选择性检测。由DMF诱导的三苯基吡咯羧酸衍生物(TPPA)重结晶在固态时出现可控的荧光发射,它具备很好的温度选择性,响应迅速,并可以循环利用,这证明TPPA可以作为一种热响应材料用于温度监控设备中。     

Highly Emissive Diborylphenylene‐Containing Bis(phenylethynyl)benzenes: Structure–Photophysical Property Correlations and Fluoride Ion Sensing

A series of 2,5‐bis(dimesitylboryl)‐1,4‐bis(arylethynyl)benzenes 1 – 6 that contain various p‐substituents on the terminal benzene rings, including NPh₂ ( 1 ), OMe ( 2 ), Me ( 3 ), H ( 4 ), CF₃ ( 5 ), and CN ( 6 ) groups, were synthesized, and the effects of the p‐substituents on the absorption and fluorescence properties were investigated both in solution and in the solid state. Linear relationships were obtained not only between the Hammett σ_p⁺ constants of the p‐substituents and the absorption and fluorescence maxima, quantum yields, and excited‐state dynamics parameters in solution, but also between the σ_p⁺ constants and the fluorescence quantum yields in the solid state. An important finding extracted from these results is that the suppressed fluorescence quenching in the solid state is a common feature for the present laterally boryl‐substituted π‐conjugated skeletons. Hence, the diborylphenylene can serve as a useful core unit to develop highly emissive organic solids. In fact, most of the derivatives showed more intense emission in the solid state than in solution. In addition to these studies, the titration experiment of 1 by the addition of nBu₄NF was conducted, which showed the stepwise bindings of two fluoride ions with high association constants as well as a drastic change in the fluorescence spectra, while constantly maintaining high quantum yields (0.61–0.76), irrespective of the binding modes. This result also demonstrated the potential utility of the present molecules as an efficient fluorescent fluoride ion sensor.     

D-A结构的9,9-二芳基芴类发光材料的合成、表征及性能

设计合成了一系列以三苯胺结构为核心的具有推电子-拉电子(D-A)结构的9,9-二芳基芴类有机小分子. 研究了介质极性对吸收与发射光谱行为的影响及分子结构与其发光能力的关系. 该类化合物荧光发射波长范围在430-530 nm. 并在特定极性溶剂中观察到双重荧光现象. 溶剂效应显示该类化合物随着介质极性的增加, 分子内电荷转移态(ICT)的荧光发射峰波长先红移后蓝移且荧光强度降低, 表现出扭曲的分子内电荷转移(TICT)行为. 该类化合物的最高占有分子轨道(HOMO)能级位于-5.24 - -5.50 eV, 且可以通过改变取代基电负性的强弱来调节. 所得化合物的玻璃化转变温度为192-206 °C, 热重分析(TGA)表明化合物的热分解温度都在400 °C以上, 具有良好的热稳定性.     

Energy transfer in calixarene-based cofacial-positioned perylene bisimide arrays

The synthesis of multichromophoric perylene bisimide-calix[4]arene arrays with up to five perylene units (containing orange, violet, and green perylene bisimide chromophores) and of monochromophoric model compounds was achieved by subsequent imidization of mono-Boc functionalized calix[4]arene linkers with three different types of perylene bisimide dye units. The optical properties of all compounds were studied with UV/vis absorption and steady state and time-resolved fluorescence spectroscopy. Upon excitation of the inner orange dye at 490 nm of array 3, strong fluorescence emission of the outer green perylene bisimide (PBI) chromophore at 744 nm is observed. The fluorescence excitation spectra of compounds 3 and 4 (lambdadet = 850 nm) show all absorption bands of the parent chromophores (e.g., all perylene units contribute to the emission from S1 state of the green PBI). Thus, the fluorescence emission and excitation spectra as well as time-resolved data of fluorescence lifetimes in the absence (tauD = 5.1 ns) and in the presence of an acceptor (tauDA = 0.8 ns) suggest efficient energy transfer processes between the perylene bisimide dye units. For the bichromophoric array 4, the energy transfer rate is calculated to a value of 1.05 x 109 s-1. These results demonstrate highly efficient energy transfer in cofacially assembled dye arrays.     

Ring‐Shaped Silafluorene Derivatives as Efficient Solid‐State UV‐Fluorophores: Synthesis,Characterization, and Photoluminescent Properties

Four ring‐shaped silafluorene‐containing compounds ( 1 – 4 ) were synthesized and characterized as potentially promising monomers for fluorescent polymers. Their optical properties in solution and solid state (thin film and powder) were studied. These compounds have low quantum yields in solution (Φ_fl=0.13‐0.15) with fluorescence maxima at about 355 nm, but high quantum yields in the solid state (powder, Φ_fl=0.35‐0.54) with fluorescence maxima at about 377 and 488 nm. Influence of the substituents and the number of silafluorene units in 1 – 4 on their optical properties was investigated. Extensive study of the X‐ray crystal structures of 1 – 4 was undertaken to analyze and qualitatively estimate the role, extent, and influence of silafluorene moieties’ interactions on solid‐state fluorescent properties. Excited state UV/Vis and theoretical molecular orbital (MO) calculations were performed to explore possible fluorescence mechanisms and differences in quantum yields among these compounds.     

Synthesis and electronic properties of expanded 5-(hetero)aryl-thien-2-yl substituted 3-ethynyl quinoxalines with AIE characteristics

Expanded 5-(hetero)aryl-thien-2-yl substituted 3-ethynyl quinoxaline dyes with variable substitution pattern on the peripheral thiophene ring were synthesized in moderate to very good yields by Suzuki and Buchwald-Hartwig coupling of the corresponding brominated 3-ethynyl quinoxalines. Dumbbell-shaped bis(thienyl 3-ethynyl quinoxalines) are also accessible by the Suzuki protocol. The photophysical properties were investigated by UV and fluorescence spectroscopy. Most of the obtained compounds display fluorescence in solution and some of them also in the solid state. Additionally, tuning of the emission color of the quinoxaline based chromophores can be conveniently accomplished by the remote substituent group. The determined absorption and emission maximum as well as the Stokes shifts strongly correlate with Hammett σp+parameters. Besides,photophysical properties of selected derivatives in the solid state, biphasic solutions, and PMMA films, along with their relationships, are comparatively investigated. Moreover, two 5-(hetero)aryl-thien-2-yl substituted 3-ethynyl quinoxaline dyes are aggregation induced emission(AIE) chromophores indicated by restriction of molecular motions. A covalently restricted 3-ethynyl quinoxaline supports that the inhibition of molecular rotation is responsible for the significant enhancement of fluorescence in acetonitrile/water mixtures.     

A Luminescent Nitrogen‐Containing Polycyclic Aromatic Hydrocarbon Synthesized by Photocyclodehydrogenation with Unprecedented Regioselectivity

We present a nitrogen‐containing polycyclic aromatic hydrocarbon (N‐PAH), namely 12‐methoxy‐9‐(4‐methoxyphenyl)‐5,8‐diphenyl‐4‐(pyridin‐4‐yl)pyreno[1,10,9‐h,i,j]isoquinoline (c‐TPE‐ON), which exhibits high quantum‐yield emission both in solution (blue) and in the solid state (yellow). This molecule was unexpectedly obtained by a three‐fold, highly regioselective photocyclodehydrogenation of a tetraphenylethylene‐derived AIEgen. Based on manifold approaches involving UV/Vis, photoluminescence, and NMR spectroscopy as well as HRMS, we propose a reasonable mechanism for the formation of the disk‐like N‐PAH that is supported by density functional theory calculations. In contrast to most PAHs that are commonly used, our system does not suffer from entire fluorescence quenching in the solid state due to the peripheral aromatic rings preventing π–π stacking interactions, as evidenced by single‐crystal X‐ray analysis. Moreover, its rod‐like microcrystals exhibit excellent optical waveguide properties. Hence, c‐TPE‐ON comprises a N‐PAH with unprecedented luminescent properties and as such is a promising candidate for fabricating organic optoelectronic devices. Our design and synthetic strategy might lead to a more general approach to the preparation of solution‐ and solid‐state luminescent PAHs.     

Spectral and photophysical studies on cruciform oligothiophenes in solution and the solid state

The photophysical and spectroscopic properties of a new class of oligothiophene derivatives, designated as cruciform oligomers, have been investigated in solution (room and low temperature) and in the solid state (as thin films in Zeonex matrixes). The study comprises absorption, emission, and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion, and singlet oxygen formation) and lifetimes. The overall data allow the determination of the rate constants for all decay processes. From these, several conclusions are drawn. First, in solution, the main deactivation channels for the compounds are the radiationless processes: S(1) --> S(0) internal conversion and S(1) --> T(1) intersystem crossing. Second, in general, in the solid state, the fluorescence quantum yields decrease relative to solution. A comparison is made with the analogous linear alpha-oligothiophenes, revealing a lower fluorescence quantum efficiency and, in contrast to the normal oligothiophenes, that internal conversion is an important channel for the deactivation of the singlet excited state. Replacement of thiophene by 1,4-phenylene units in the longer-sized cruciform oligomer increases the fluorescence efficiency. The highly efficient generation of singlet oxygen through energy transfer from the triplet state (S(Delta) approximately 1) provides support for the measured intersystem crossing quantum yields and suggests that reaction with this may be an important pathway to consider for degradation of devices produced with these compounds.