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.     

Novel fluorescent N,O-chelated fluorine-boron benzamide complexes containing thiadiazoles: Synthesis and fluorescence characteristics

A series of N-(5-phenyl-1,3,4-thiadiazol-2-yl)benzamide derivatives and their corresponding BF₂ complexes were synthesized, and their photophysical properties were determined. The effect of the derivatives with various substituents on the benzamide ring and phenyl-1, 3, 4-thiadiazole ring were examined in different organic solvents and in the solid state. These dyes enjoy a series of excellent photophysical properties including the large Stokes shift, solid-state fluorescence, and aggregation-induced emission effect (AIEE).     

Five-membered 2,3-dioxo heterocycles: LII. Reactions of 5-aryl-4-(quinoxalin-2-yl)-2,3-dihydrofuran-2,3-diones with Schiff bases and dicyclohexylcarbodiimide. Crystalline and molecular structure of substituted 2-(4-oxo-3,4-dihydro-2<Emphasis Type="Italic">H</Emphasis>1,3-oxazin-5-yl)quinoxalines

Aroyl(quinoxalinyl)ketenes generated by thermolysis of 5-aryl-4-(quinoxalin-2-yl)-2,3-dihydrofuran-2,3-diones react with N-benzylideneanilines and N,N’-dicyclohexylcarbodiimide according to the [4+2]-cycloaddition pattern where the aroylketene acts as diene, and C=N component, as dienophile, to give 3-aryl-2-(2,3,6-triaryl- and 6-aryl-3-cyclohexyl-2-cyclohexylimino-4-oxo-3,4-dihydro-2H-1,3-oxazin-5-yl)quinoxalines. The structure of two cycloaddition products was proved by X-ray analysis.     

Dramatically Enhanced Fluorescence of Heteroaromatic Chromophores upon Insertion as Spacers into Oligo(triacetylene)s

In continuation of a previous study on the modulation of π‐electron conjugation of oligo(triacetylene)s by insertion of central hetero‐spacer fragments between two (E)‐hex‐3‐ene‐1,5‐diyne ((E)‐1,2‐diethynylethene, DEE) moieties (Fig. 1), a new series of trimeric hybrid oligomers ( 14 – 18 and 22 – 24 , Fig. 2) were prepared (Schemes 1–3). Spacers used were both electron‐deficient (quinoxaline‐based heterocycles, pyridazine) and electron‐rich (2,2′‐bithiophene, 9,9‐dioctyl‐9H‐fluorene) chromophores. With 19–21 (Scheme 4), a series of transition metal complexes was synthesized as potential precursors for nanoscale scaffolding based on both covalent acetylenic coupling and supramolecular assembly. The UV/VIS spectra (Fig. 3) revealed that the majority of spacers provided hetero‐trimers featuring extended π‐electron delocalization. The new hybrid chromophores show a dramatically enhanced fluorescence compared with the DEE dimer 13 and homo‐trimer 12 (Fig. 5). This increase in emission intensity appears as a general feature of these systems: even if the spacer molecule is non‐fluorescent, the corresponding hetero‐trimer may show a strong emission (Table 2). The redox properties of the new hybrid chromophores were determined by cyclic voltammetry (CV) and rotating‐disk voltammetry (RDV) (Table 3 and Fig. 5). In each case, the first one‐electron reduction step in the hetero‐trimers appeared anodically shifted compared with DEE dimer 13 and homo‐trimer 12 . With larger spacer chromophore extending into two dimensions (as in 14 – 18 , Fig. 2), the anodic shift (by 240–490 mV, Table 3) seems to originate from inductive effects of the two strongly electron‐accepting DEE substituents rather than from extended π‐electron conjugation along the oligomeric backbone, as had previously been observed for DEE‐substituted porphyrins.     

Dipolar Dyes with a Pyrrolo[2,3‐b]quinoxaline Skeleton Containing a Cyano Group and a Bridged Tertiary Amino Group: Synthesis,Solvatofluorochromism, and Bioimaging

Two strongly polarized dipolar chromophores possessing a cyclic tertiary amino group at one terminus of the molecule and a CN group at the opposite terminus were designed and synthesized. Their rigid skeleton contains the rarely studied pyrrolo[2,3‐b]quinoxaline ring system. The photophysical properties of these regioisomeric dyes were different owing to differing π conjugation between the CN group and the electron‐donor moiety. These dipolar molecules showed very intense emission, strong solvatofluorochromism, and sufficient two‐photon brightness for bioimaging. One of these regioisomeric dyes, namely, 11‐carbonitrile‐2,3,4,5,6,7‐hexahydro‐1H‐3a,8,13,13b‐tetraazabenzo[b]cyclohepta[1,2,3‐jk]fluorene, was successfully utilized in two‐photon imaging of mouse organ tissues and showed distinct tissue morphology with high resolution.     

Synthesis and application of ethyl 3-(4-dialkylaminophenyl)-2-(quinoxalin-3(4H)-on-2-yl)propenoates and related products

Ethyl quinoxalin-3( 4 H)-on-2-ylacetate was prepared by the condensation of 1,2-diaminobenzene and diethyl oxalacetate (sodium salt). The key quinoxaline intermediate was condensed with a variety of 4-dialkylaminobenzaldehydes/substituted benzaldehydes to yield novel brilliant quinoxalin-2-yl styryl dyes which were applied on polyester fibers as disperse dyes and their dyeing properties were studied.     

Synthesis of functional derivatives of isothiazole and isoxazole basing on (5-arylizoxazol-3-yl)- and (4,5-dichloroisothiazol-3-yl)arylmethanol

From (4,5-dichloroisothiazol-3-yl)phenylmethanol by Ritter reaction a substituted acetamide was synthesized that at hydrolysis with HCl afforded (4,5-dichloroisothiazol-3-yl)phenylmethylamine hydrochloride. By reaction of (5-arylisoxazol-3-yl)- and 4,5-dichloroisothiazol-3-yl)arylmethanol with thionyl chloride the corresponding (1,2-azol-3-yl)arylchloromethanes were obtained. At treatment with O- and N-nucleophiles chlorine atom in chloromethylеne fragment of obtained compounds was substituted by residues of benzylamine, morpholine, vanillin, and ethoxy group.     

Theoretic and Experimental Study of Photoprocesses in Substituted 4-Dicyanomethylene-4H-pyrans

The photoprocesses in substituted 4-dicyanomethylene-4H-pyran (DCM) derivatives were studied theoretically and experimentally. The experimental spectral and luminescent parameters of the molecules under study are in good agreement with the results of quantum-chemical calculations. Trends changes in the spectral and luminescent properties depending on the molecular structure were established. The appearance of the S₂ level near the S₁ level in the scheme of the energy states of symmetrically substituted DCM (bis-DCM) causes changes in photophysical processes and a drop in the fluorescence quantum yield.     

Microwave assisted synthesis of substituted (<Emphasis Type="Italic">Z</Emphasis>)-2-{[1-phenyl-3-(thiophen-2-yl)-1<Emphasis Type="Italic">H</Emphasis>-pyrazol- 4-yl]methylene}benzofuran-3(2<Emphasis Type="Italic">H</Emphasis>)-ones and their antimicrobial activity

Aurones, pyrazole and thiophene scaffolds are known for their potential antimicrobial activity. Herein, we have synthesized hybrid compounds containing three substituted (Z)-2-{[1-phenyl-3-(thiophen-2-yl)- 1H-pyrazol-4-yl]methylene}benzofuran-3(2H)-ones that had been produced from substituted (E)-1-(2-hydroxyphenyl)- 3-[1-phenyl-3-(thiophen-2-yl)-1H-pyrazol-4-yl]prop-2-en-1-ones in high yields. All synthesized compounds were tested in vitro for their antimicrobial activity. Several of those demonstrated promising activity against some fungal and bacterial strains.     

Preparation,characterization of new Co(II) and Cu(II) phthalocyanines and their catalytic performances in aerobic oxidation of substituted phenols

The host–guest inclusion complex of meta-cresol (m-cresol, liquid at room temperature, guest molecule) is synthesized with β-cyclodextrin (β-CD, host molecule). The inclusion complex is characterized by various techniques like nuclear magnetic resonance, powder X-ray diffraction, field emission scanning electron microscopy and spectroscopic (steady state as well as time-resolved) techniques. To the best of our knowledge, no literature data is available on the photophysical properties (especially fluorescence upon photoexcitation) of m-cresol in liquid media till date. Our spectroscopic studies exhibit some interesting photophysical properties of m-cresol and its inclusion complex with β-CD in different liquid media. The present work is important in view of the various potential applications of m-cresol in science, technology and medicine.     

Catalytic alkylation of cycloalkaneindoles and tetrahydro-γ-carboline with 9-oxiranylmethylcarbazole

Catalytic alkylation of substituted indoles such as cycloalkaneindoles and tetrahydro-γ-carboline using 9-oxiranylmethylcarbazole leads to the formation of 1-(carbazol-9-yl)-3-{dihydrocycloalkane[b]indol-4(1H)-yl}propan-2-ols and 1-(carbazol-9-yl)-3-{2,8-dimethyl-3,4-dihydro-1H-pyrido[4,3-b]indol-5(2H)-yl}propan-2-ol, conjugates containing 2-hydroxypropylene spacer.     

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.     

两个新的苯并噻唑衍生物的合成与光物理性质

以苯并噻唑、苯乙酰基和吡啶阳离子为电子受体,二乙烯基苯为共轭桥,合成了两个新的A-π-A′型苯并噻唑衍生物:4-(2-苯并噻唑)-乙烯基查尔酮(1)和4-{4-[2-(苯并噻唑)乙烯基]苯乙烯基}-N-甲基吡啶碘盐(2).研究了它们在溶液和固体基质中的光物理性质.研究发现:染料2由于具有较强的极性和较好的平面性,从而具有较长的吸收、发射峰和较强的荧光发射.有机染料在聚甲基丙烯酸甲酯/溶胶-凝胶复合玻璃中的发光行为与聚甲基丙烯酸甲酯和溶胶-凝胶玻璃二者的基质性质有关,同时由于固体基质中分子发生聚集的可能性降低,荧光强度相对于同浓度溶液增强,稳定性提高.     

Synthesis of new aryl(hetaryl)vinyl-substituted benzo[<Emphasis Type="Italic">f</Emphasis>]quinolines and 4,7-phenanthrolines

Previously unknown 1-[2-aryl(quinolin-2-yl)ethenyl]-3-[aryl(quinolin-2-yl)]benzo[f]quinolines and 3-aryl-1-(2-arylethenyl)-4,7-phenanthrolines were synthesized by reactions of 1-methylbenzo[f]quinolines and 1-methyl-4,7-phenanthrolines with substituted N-benzylideneanilines and N-(quinolin-2-ylmethylidene)aniline on heating in dimethylformamide in the presence of potassium hydroxide.     

Synthesis of pyrrolo[1,2-a]quinoxalines by 1,3-dipolar cycloaddition reaction. An additional reaction mechanism via an aziridine intermediate

The reaction of the 2-substituted 6-chloroquinoxaline 4-oxides 1a or 1b with 2-fold molar amount of methyl propiolate resulted in the 1,3-dipolar cycloaddition reaction to give 8-chloro-1,3-bismethoxycarbonyl-4-(piperidin-1-yl)pyrrolo[1,2-a]quinoxaline 4a or 8-chloro-1,3-bismethoxycarbonyl-4-(morpholin-4-yl)pyrrolo-[1,2-a]quinoxaline 4b , respectively. Compound 4a or 4b was transformed into 8-chloro-3-methoxycarbonyl-4-(piperidin-1-yl)pyrrolo[1,2-a]quinoxaline 5a or 8-chloro-3-methoxycarbonyl-4-(morpholin-4-yl)pyrrolo[1,2-a]-quinoxaline 5b , respectively. The structure of 4a,b was confirmed by the NOE measurement among the C₁ -H , C ₂-H and C ₉-H proton signals of 5a,b . An additional reaction mechanism was proposed for the ring transformation of isoxazolo[2,3-a]quinoxalines into pyrrolo[1,2-a]quinoxalines.     

Blue‐to‐Orange Color‐Tunable Laser Emission from Tailored Boron‐Dipyrromethene Dyes

A series of meso‐substituted boron‐bipyrromethene (BODIPY) dyes are synthesized and their laser and photophysical properties systematically studied. Laser emission covering a wide visible spectral region (from blue to orange) is obtained by just changing the electron donor character of the heteroatom at position 8. The additional presence of methyl groups at positions 3 and 5 results in dyes with a photostability similar to that of the unsubstituted dye but with much improved efficiency. Correlation of the lasing properties of the different dyes to their photophysical properties provides inklings to define synthetic strategies of new BODIPY dyes with enhanced efficiency and modulated wavelength emission over the visible spectral region.     

Synthesis of 4(pyrazol-3-yl)[1,2,4]triazolo[4,3-a]quinoxalines and tetrazolo analog

The transformation of 2-chloro-3-[5-(acetoxymethyl)-1-phenylpyrazol-3-yl]quinoxaline 3 to 1-aryl-4-[5-(hydroxymethyl-1-phenylpyrazol-3-yl][1,2,4]triazolo[4,3-a]quinoxalines 4a-c has been achieved upon treatment with aroylhydrazines in boiling butanol. Compounds 4a-c were smoothly acetylated by acetic anhydride to give their acetyl derivatives 5a-c in good yield. 4-[5-(Acetoxymethyl)-1-phenylpyrazol-3-yl]-1-methyl[1,2,4]triazolo[4,3-a]quinoxaline was prepared by ring closure of 2-hydrazino-3-[5-(hydroxymethyl)-1-phenylpyrazol-3-yl]quinoxaline 6 by the action of acetic anhydride. The reaction of 6 with acetylacetone afforded 3-[5-(hydroxymethyl)-1-phenylpyrazol-3-yl]-2-(3,5-dimethylpyrazol-1-yl)quinoxaline 8 . In addition, the reaction of 3 with sodium azide in boiling N, N-dimethylformamide yielded the fused tetrazolo[1,5-a]quinoxaline 9 .     

Reaction of ethyl 4-[(<Emphasis Type="Italic">E</Emphasis>)-1-chloro-3-oxoprop-1-en-1-yl]-3,5-dimethyl-1<Emphasis Type="Italic">H</Emphasis>-pyrrole-2-carboxylate with hydrazines

Ethyl 4-[(E)-1-chloro-3-oxoprop-1-en-1-yl]-3,5-dimethyl-1H-pyrrole-2-carboxylate reacted with substituted hydrazines in different solvents to give mixtures of regioisomeric 3- and 5-substituted pyrazoles. Conditions were found for selective formation of 1-aryl(alkyl)-5-(5-ethoxycarbonyl-2,4-dimethyl-1H-pyrrol-3-yl)-1H-pyrazoles.     

Reactions of 3-Aroylpyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxaline-1,2,4(5<Emphasis Type="Italic">H</Emphasis>)-triones with 2,3-Dihydrofuran and 3,4-Dihydro-2<Emphasis Type="Italic">H</Emphasis>-pyran

3-Aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones reacted with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran to give mixtures of the corresponding hetero-Diels–Alder (furo- and pyrano[3″,2″: 5′,6′]pyrano- [4′,3′: 2,3]pyrrolo[1,2-a]quinoxalines) and Michael adducts (furyl- and pyranylpyrrolo[1,2-a]quinoxalines).     

Polyfused nitrogen heterocycles: XIX. Oxidative imidazo-fusion of 3-benzoylquinoxalin-2-ones with benzylamines in the synthesis of bis(imidazo[1,5-a]quinoxalin-1- and -5-yl) derivatives

Oxidative cyclocondensation of bis(3-benzoylquinoxalin-1-yl)alkanes and oxaalkanes with benzylamine and 3-benzoylquinoxalinones with m-xylylenediamine proceeded with the formation of bis-(imidazo[1,5-a]quinoxalinyl) derivatives where the hetaryl fragments were linked by a spacer both through the imidazole and quinoxaline fragments