1,2,5-Triphenylpyrrole Derivatives with Dual Intense Photoluminescence in Both Solution and the Solid State: Solvatochromism and Polymorphic Luminescence Properties

Five organic luminophores, 1,2,5-triphenylpyrrole (TPP) derivatives 3 a – e bearing electron-withdrawing or electron-donating groups, have been synthesized by Pd-catalyzed Suzuki coupling of 1-phenyl-2,5-di(4′-bromophenyl)pyrrole and para-substituted phenylboronic acid derivatives. They possess good thermal stabilities with high decomposition temperatures above 310 °C. Investigation of the photophysical properties of the luminogens 3 a – e indicated that they exhibited dual intense photoluminescence in both solution and the solid state due to their twisted conformations, and their fluorescence quantum yields (Φ_F) were determined as 68.7–94.9 % in THF solution and 19.1–52.0 % in solid powder form. Compounds 3 a – c bearing electron-accepting groups exhibited remarkable solvatochromism with large Stokes shifts, attributable to their D-π-A structure and intramolecular charge-transfer effect. In particular, 3 a , bearing aldehyde groups, displayed an obvious red-shift of the emission band from 445 to 564 nm with increasing solvent polarity. However, no obvious solvatochromic behavior was observed for compounds 3 d , e bearing electron-donating groups. The luminophore 3 a exhibited polymorphic luminescence properties and crystallization-induced emission enhancement.     

Color‐Tunable Solid‐State Fluorescence Emission from Carbazole‐Based BODIPYs

Several carbazole‐based boron dipyrromethene (BODIPY) dyes were synthesized by organometallic approaches. Thiazole, benzothiazole, imidazole, benzimidazole, triazole, and indolone substituents were introduced at the 1‐position of the carbazole moiety, and boron complexation of each dipyrrin generated the corresponding compounds 1 , 2 a , and 3 – 6 . The properties of these products were investigated by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X‐ray crystallography, and DFT calculations. These compounds exhibited large Stokes shifts, and compounds 1 , 2 a , and 3 – 5 fluoresced both in solution and in the solid state. Complex 2 a showed the highest fluorescence quantum yield (Φ_F) in the solid state, therefore boron complexes of the carbazole–benzothiazole hybrids 2 b – f , which had several different substituents, were prepared and the effects of the substituents on the photophysical properties of the compounds were examined. The fluorescence properties showed good correlation with the results of crystal‐packing analyses, and the dyes exhibited color‐tunable solid‐state fluorescence.     

Remote Effect from Boron Cluster: Tunable Photophysical Properties of o-Carborane-Based Luminogens

We proposed a new molecular design strategy that the o-carboranyl group is attached as “an innocent unit” to the remote side of luminogens to tune photophysical properties. To verify this strategy, two o-carborane-based compounds with asymmetric molecular geometry were designed and synthesized. Photophysical properties of o-carborane-based luminogens were investigated on the basis of UV-Vis spectra, photoluminescence spectra, crystal structure analysis and theoretical calculations. The results indicate that the o-carboranyl group has a slight effect on the energy gap between the ground state (S₀) and the first excited state (S₁) in the solution state but a significant effect on the energy gap between S₀ and S₁ in the solid state. Besides, the radiative and non-radiative transition processes are modulated by the o-carboranyl unit. This leads to emission quenching in the solution state but an enhanced luminous efficiency in the aggregate state with a typical aggregation-induced emission (AIE) property.     

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.     

Simple cuprous iodide complex‐based crystals with deep blue emission and high photoluminescence quantum yield up to 100%

Luminescent cuprous complexes have attracted much attention due to their low cost, rich photophysical properties, and hence extensive applications in various fields. In this work, we report the synthesis, structure and photophysical properties of a simple and highly efficient deep blue emission cuprous iodide complex, namely CuI (PPh₃)₂(t‐BuPy), where PPh₃ and t‐BuPy stand for triphenylphosphine and 4‐tert‐butylpyridine, respectively. The complex was synthesized with a one‐pot method, and showed a super high photoluminescence quantum yield up to 100% and a maximum emission wavelength at 454 nm in crystals at room temperature. Based on density functional theory calculation, the emission likely comes from iodide to 4‐tert‐butylpyridine charge transfer and some copper to 4‐tert‐butylpyridine charge transfer excited states. Two reference complexes, CuI (PPh₃)₂(IQu) (IQu = isoquinoline) and Cu₂I₂(PPh₃)₂(t‐BuPy)₂, were also synthesized, and the photophysical properties of the three compounds in various forms such as crystalline powder, thin film and solution at both room temperature and 77 K were studied for comparison. These results give clues on how the N‐heteroaromatic ligand (4‐tert‐butylpyridine vs. isoquinoline), coordinating style (mononuclear vs. binuclear), sample form (crystalline powder vs. thin film vs. solution) and temperature (room temperature vs. 77 K) affect the photophysical properties of luminescent cuprous iodide complex.     

Synthesis and Structure-Photophysics Evaluation of 2-N-Amino-quinazolines: Small Molecule Fluorophores for Solution and Solid State

2-N-aminoquinazolines were prepared by consecutive S_NAr functionalization. X-ray structures display the nitrogen lone pair of the 2-N-morpholino group in conjugation with the electron deficient quinazoline core and thus representing electronic push-pull systems. 2-N-aminoquinazolines show a positive solvatochromism and are fluorescent in solution and in solid state with quantum yields up to 0.73. Increase in electron donor strength of the 2-amino substituent causes a red-shift of the intramolecular charge transfer (ICT) band (300–400 nm); whereas the photoluminescence emission maxima (350–450 nm) is also red-shifted significantly along with an enhancement in photoluminescence efficiency. HOMO-LUMO energies were estimated by a combination of electrochemical and photophysical methods and correlate well to those obtained by computational methods. ICT properties are theoretically attributed to an excitation to Rydberg-MO in SAC-CI method, which can be interpreted as n-π* excitation. 7-Amino-2-N-morpholino-4-methoxyquinazoline responds to acidic conditions with significant increases in photoluminescence intensity revealing a new turn-on/off fluorescence probe.     

Tridentate Complexes of Palladium(II) and Platinum(II) Bearing bis‐Aryloxide Triazole Ligands: A Joint Experimental and Theoretical Investigation

A novel class of palladium(II) and platinum(II) complexes bearing tridentate bis‐aryloxide triazole ligands was prepared by using straightforward and high‐yielding synthetic routes. The complexes were fully characterized and the molecular structures of four derivatives were unambigously determined by single‐crystal X‐ray diffractometric analyses. For the most promising luminescent Pt^II derivatives, further experimental investigations were carried out to characterize their photophysical features and to ascertain the nature of the emitting excited state by means of electronic absorption, steady‐state, and time‐resolved emission techniques in different conditions. In degassed fluid solution the complexes displayed broad and featureless photoluminescence with λ_em=522–585 nm, excited‐state lifetime up to few microseconds and quantum yield (PLQY) up to 17 %, depending on the nature of both ancillary ligand and substituent on the tridentate ligand. Computational investigation using density functional theory and time‐dependent DFT were performed to gain insight into the electronic processes responsible for optical transitions and structure–photoluminescence relationship. Jointly, experimental and theoretical characterization indicated that the radiative transition arises from an excited state with admixed triplet‐manifold metal‐to‐ligand charge transfer and ligand‐centered (³MLCT/³LC) character. We elucidated the modulation of the photophysical properties upon variation of substituents for this new family of complexes.     

Driving the Emission Towards Blue by Controlling the HOMO-LUMO Energy Gap in BF2-Functionalized 2-(Imidazo[1,5-a]pyridin-3-yl)phenols

Several boron compounds with 2-(imidazo[1,5-a]pyridin-3-yl)phenols, differentiated by the nature of the substituent (R) in the para position of the hydroxy group, have been synthesized and thoroughly characterized both in solution (¹H, ¹³C, ¹¹B, ¹⁹F NMR) and in the solid state (X-ray). All derivatives displayed attractive photophysical properties like very high Stokes shift, high fluorescence quantum yields and a good photostability in solution. Time-Dependent Density Functional Theory (TD-DFT) calculations allowed to define the main electronic transitions as intra ligand transitions (¹ILT), which was corroborated by the Natural Transition Orbitals (NTOs) shapes. The HOMO-LUMO energy gap was correlated to the electronic properties of the substituent R on the phenolic ring, as quantified by its σ_p Hammett constant.     

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.     

Experimental and Computational Study on Photophysical Properties of Mesoionic Chalcogenones

N-Heterocyclic carbene adducts with main group elements (NHC=E) have aroused great interest and have been widely investigated in coordination chemistry. Among them, N-heterocyclic carbene adducts with chalcogens (NHC=Ch) have been known for a long time. Their investigations mostly focused on synthesis, coordination chemistry and electrochemistry. Their photophysical properties still remain unexplored. In this work, the photophysical properties of mesoionic carbene adducts with sulfur and selenium have been investigated both in solution and solid state. These compounds showed blue fluorescence in dichloromethane. While in solid state, orange to red room-temperature phosphorescence can be observed, and dual emission was found in mesoionic thiones. Furthermore, time-dependent density functional theory (TD-DFT) calculations were used to obtain insights into the luminescent mechanism.     

Random Copolymers of Styrene with Pendant Fluorophore Moieties: Synthesis and Applications as Fluorescence Sensors for Nitroaromatics

Five random copolymers comprising styrene and styrene with pendant fluorophore moieties, namely pyrene, naphthalene, phenanthrene, and triphenylamine, in molar ratios of 10:1, were synthesized and employed as fluorescent sensors. Their photophysical properties were investigated using absorption and emission spectral analyses in dichloromethane solution and in solid state. All copolymers possessed relative quantum yields up to 0.3 in solution and absolute quantum yields up to 0.93 in solid state, depending on their fluorophore components. Fluorescence studies showed that the emission of these copolymers is highly sensitive towards various nitroaromatic compounds, both in solution and in the vapor phase. The detection limits of these fluorophores for nitroaromatic compounds in dichloromethane solution proved to be in the range of 10⁻⁶ to 10⁻⁷ mol/L. The sensor materials for new hand-made sniffers based on these fluorophores were prepared by electrospinning and applied for the reliable detection of nitrobenzene vapors at 1 ppm in less than 5 min.     

Dendrimers with a Pentaphenylene Core: A Photophysical Study

Novel dendrimers G2PC and G4PC consisting of a p‐pentaphenylene core ( PC ) appended in the para position with two second‐generation ( G2 ) or two fourth‐generation ( G4 ) sulfonimide branches and two n‐octyl chains, as well as a model compound of the pentaphenylene core ( G0PC ), are prepared. The photophysical properties (absorption, emission, and excitation spectra; fluorescence decay lifetime; and fluorescence anisotropy spectra) of the three compounds are investigated under different experimental conditions (dichloromethane solution and solid state at 293 K, dichloromethane/methanol rigid matrix at 77 K). In the absorption spectra contributions from both the branches and the core can be clearly identified. The fluorescence spectra show only the characteristic fluorescence of the pentaphenylene unit with λ_max around 410 nm in fluid solution and 420 nm in the solid state. In solution the fluorescence quantum yields are 0.78, 0.76, and 0.72 for G0PC , G2PC , and G4PC , respectively, and the fluorescence lifetime is about 0.7 ns in all cases. Energy transfer from the chromophoric groups of the dendrimer branches to the core does not occur. The three compounds show the same, high steady‐state anisotropy value (0.35) in dilute rigid‐matrix solution at 77 K. In dichloromethane at 293 K, the increasing anisotropy values along the series G0PC (0.17), G2PC (0.27), and G4PC (0.32), with increasing molecular volume of the three compounds, show that depolarization takes place by molecular rotation. In the solid state the anisotropy is very low (0.015, 0.017, and 0.035 for G0PC , G2PC , and G4PC , respectively), probably because of fast depolarization via energy migration.     

Meso位单取代卟啉及其配合物的合成、表征和光谱性质

设计合成了一系列新型的meso位N,N-二甲氨基苯基或N-苯基咔唑基单取代卟啉（5a~c）及其锌配合物（6a~c）,用高分辨质谱、¹H NMR、紫外-可见光谱及X射线单晶衍射方法等对结构进行了表征;研究了卟啉化合物及其配合物的热稳定性及荧光性质。结果表明,这些卟啉化合物及其锌配合物在400~410 nm之间具有强的吸收且具有很好的热稳定性,荧光量子产率在0.05~0.09;另外还分析了meso位不同取代基对光谱性质的影响。     

Optoelectronic,Aggregation, and Redox Properties of Double-Rotor Boron Difluoride Hydrazone Dyes

We develop the chemistry of boron difluoride hydrazone dyes (BODIHYs) bearing two aryl substituents and explore their properties. The low-energy absorption bands (λ_max=427–464 nm) of these dyes depend on the nature of the N-aryl groups appended to the BODIHY framework. Electron-donating and extended π-conjugated groups cause a redshift, whereas electron-withdrawing groups result in a blueshift. The title compounds were weakly photoluminescent in solution and strongly photoluminescent as thin films (λ_PL=525–578 nm) with quantum yields of up to 18 % and lifetimes of 1.1–1.7 ns, consistent with the dominant radiative decay through fluorescence. Addition of water to THF solutions of the BODIHYs studied causes molecular aggregation which restricts intramolecular motion and thereby enhances photoluminescence. The observed photoluminescence of BODIHY thin films is likely facilitated by a similar molecular packing effect. Finally, cyclic voltammetry studies confirmed that BODIHY derivatives bearing para-substituted N-aryl groups could be reversibly oxidized (E_ox1=0.62–1.02 V vs. Fc/Fc⁺) to their radical cation forms. Chemical oxidation studies confirmed that para-substituents at the N-aryl groups are required to circumvent radical decomposition pathways. Our findings provide new opportunities and guiding principles for the design of sought-after multifunctional boron difluoride complexes that are photoluminescent in the solid state.     

Spectroscopic Properties of Amine‐substituted Analogues of Firefly Luciferin and Oxyluciferin

Spectroscopic and photophysical properties of firefly luciferin and oxyluciferin analogues with an amine substituent (NH₂, NHMe and NMe₂) at the C6' position were studied based on absorption and fluorescence measurements. Their π‐electronic properties were investigated by DFT and TD‐DFT calculations. These compounds showed fluorescence solvatochromism with good quantum yields. An increase in the electron‐donating strength of the substituent led to the bathochromic shift of the fluorescence maximum. The fluorescence maxima of the luciferin analogues and the corresponding oxyluciferin analogues in a solvent were well correlated with each other. Based on the obtained data, the polarity of a luciferase active site was explained. As a result, the maximum wavelength of bioluminescence for a luciferin analogue was readily predicted by measuring the photoluminescence of the luciferin analogue in place of that of the corresponding oxyluciferin analogue.     

Conjugated and partially conjugated 2,5‐diphenylthiophene‐containing light‐emitting copolymers in polymeric light‐emitting diode (PLED) device fabrications

To study the effect of nonconjugation on polymeric and photophysical properties of thiophene‐containing polymers, new light‐emitting copolymers comprising either alternate 2,5‐diphenylthiophene and vinylene or alternate 2,5‐diphenylthiophene and aliphatic ether segments were synthesized. Both copolymers contained 2,5‐diphenylthiophene as the major chromophore and emitted a sky bluish fluorescence in dilute solution (10^?2 mg/mL). With a rigid and planarity structure and the concomitant crystallinity, the former copolymer (fully conjugated) possessed a higher quantum efficiency, a higher glass‐transition temperature, and a better thermal stability. In contrast, the latter copolymer (conjugated–nonconjugated) had better solubility and provided enhanced photophysical properties for the fabricated polymeric light‐emitting diode (PLED) device: at 15 V, the maximum current and brightness were 110 mA/cm² and 4289 cd/m², respectively, and the electroluminescence efficiency remained constant at approximately 4.9 cd/A in a voltage range of 8 to 14 V. The existence of intramolecular/intermolecular aggregates in the latter copolymer was corroborated from the the UV–vis and photoluminescence spectra of its solutions. With an increase in solution concentration, the shape and λ_max of the photoluminescence spectrum were redshifted. In a solution with a concentration as high as 10 mg/mL, the redshift was so drastic that the photoluminescence spectrum was nearly identical to that of a solid‐film. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6061–6070, 2004     

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.     

Synthesis,crystal structure,and photophysical properties of a double open cubane-like Cd(II) complex based on 2-substituted-8-hydroxyquinoline

A 2-substituted-8-hydroxyquinoline (E)-2-[2-(3-thienyl)ethenyl]-8-quinolinol (HL) was synthesized and characterized by ESI-MS, NMR spectroscopy, and elemental analysis. Using solvothermal method, a tetranuclear complex [Cd₄L₆Br₂]·6DMF (1) was fabricated by assembly of Cd(II) with HL. X-ray structural analysis shows that 1 exhibits a double open cubane-like core structure, which is bridged by six 8-hydroxyquinolinate-based ligands. The supramolecular structure of 1 features a 3-D porous solid constructed by aromatic stacking interactions, C–H···π interactions and C–H···O hydrogen bonds. The assembly of cadmium salts and HL in solution was investigated by UV–vis and photoluminescence. We also studied the thermal stability and photophysical properties (fluorescent emission, lifetime, and quantum yield) of 1. The results show that 1 emits yellow luminescence in the solid state.     

Photophysical and Photochemical Properties of Naturally Occurring normelinonine F and Melinonine F Alkaloids and Structurally Related N(2)‐ and/or N(9)‐methyl‐β‐carboline Derivatives

In the present work, we have synthesized and fully characterized the photophysical and photochemical properties of a selected group of N‐methyl‐β ‐carboline derivatives (9‐methyl‐β ‐carbolines and iodine salts of 2‐methyl‐ and 2,9‐dimethyl‐β ‐carbolinium) in aqueous solutions, in the pH range 4.0–14.5. Moreover, despite the quite extensive studies reported in the literature regarding the overall photophysical behavior of N‐unsubstituted β Cs, this work constitutes the first full and unambiguous characterization of anionic species of N‐unsubstituted β Cs (nor harmane, harmane and harmine), present in aqueous solution under highly alkaline conditions (pH > 13.0). Acid dissociation constants (K _a), thermal stabilities, room temperature UV –visible absorption and fluorescence emission and excitation spectra, fluorescence quantum yields (Ф _F) and fluorescence lifetimes (τ _F), as well as quantum yields of singlet oxygen production (Ф _Δ) have been measured for all the studied compounds. Furthermore, for the first time to our knowledge, chemometric techniques (MCR ‐ALS and PARAFAC ) were applied on these systems, providing relevant information about the equilibria and species involved. The impact of all the foregoing observations on the biological role, as well as the potential biotechnological applications of these compounds, is discussed.     

Comparison of Phosphorescent Pt(II) Complexes with C^N^N vs N^N^N Chelators and Caffeine-Based NHC-co-ligands†

In this work, we explored coordination compounds featuring caffeine-based carbene co-ligands and tridentate dianionic pincer luminophores derived from 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine (N), as well as from 2-phenyl-6-(1H-1,2,4-triazol-5-yl)pyridine (C), bearing either Ad (adamantyl) or tBu (tertiary butyl) substituents. The new 2-phenyl-6-(1H-1,2,4-triazol-5-yl)pyridine-based ligand precursors along with four Pt(II) complexes, namely Pt(C-tBu), Pt(C-Ad), Pt(N-tBu) and Pt(N-Ad) were characterized. Further on, the influence of the different substituents at the chelating luminophores and of the caffeine-based NHC-co-ligand on the photophysical properties (including photoluminescence quantum yields (Φ_L), excited-state lifetimes (τ), radiative (k_r), and non-radiative (k_nr) deactivation rate constants) was assessed in fluid solutions at room temperature (RT) and in frozen glassy matrices at 77 K. All four luminophores perform equivalently well within the experimental uncertainty. In deoxygenated fluid solutions at RT, photoluminescence quantum yields reaching up to 24 ± 2% and excited-state lifetimes of around 12 μs were found. The generally long excited-state lifetimes and only minor blue shift upon cooling to 77 K along with mostly well-resolved vibrational progressions point to metal-perturbed ligand-centered excited states. Notably, the yield of the complexation reaction in case of Pt(C-tBu) and Pt(C-Ad) was almost two times higher compared to Pt(N-tBu) and Pt(N-Ad). Cyclometallation is not an essential feature to achieve high photoluminescence quantum yields, but it can improve the synthetic efficiency. In summary, it can be observed that coordination chemical concepts based on natural products can lead to stable phosphorescent species with interesting excited-state properties.