Synthesis, optical and electrochemical properties of 4,4'-bibenzo[c]thiophene derivatives

We designed and synthesized unsubstituted 4,4′-bibenzo[c]thiophene 4,4′-BBT and its silyl-substituted derivatives 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT with one or two tert-butyldimethylsilyl groups on each thiophene ring, as new π-building blocks in emitters, photosensitizers and semiconductors for organic optoelectronic devices. The characterization of 4,4′-BBT, 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT was successfully determined by FTIR, ¹H and ¹³C NMR measurements, high-resolution mass spectrometry (HRMS) analysis, photoabsorption and fluorescence spectroscopy, cyclic voltammetry (CV) and density functional theory (DFT) calculations. Moreover, a single-crystal X-ray structural analysis was successfully made for 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT. The photoabsorption and fluorescence maxima (λ^abs_max and λ^fl_max) of the three 4,4′-bibenzo[c]thiophene derivatives in toluene exhibit bathochromic shifts in the order of 4,4′-BBT (359 nm and 410 nm) < 1,1′-Si-4,4′-BBT (366 nm and 420 nm) < 1,1′,3,3′-Si-4,4′-BBT (371 nm and 451 nm). The HOMO and LUMO energy levels rise in the order of 4,4′-BBT (−5.55 eV and −2.39 eV) < 1,1′-Si-4,4′-BBT (−5.45 eV and −2.34 eV) < 1,1′,3,3′-Si-4,4′-BBT (−5.34 eV and −2.30 eV), but the rise of the HOMO energy level is larger than that of the LUMO energy level, resulting in the bathochromic shift of the photoabsorption band from 4,4′-BBT to 1,1′,3,3′-Si-4,4′-BBT. The fluorescence quantum yields (Φ_fl) of 4,4′-BBT, 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT in toluene are 0.41, 0.41 and 0.36, respectively. It is worth mentioning that in the solid state 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT show relatively high Φ_fl-solid values of 0.22 and 0.25, respectively, whereas 4,4′-BBT exhibits poor solid-state fluorescence properties (Φ_fl-solid < 0.02). This work provides an efficient synthetic method for the 4,4′-bibenzo[c]thiophene derivatives and their photophysical properties in the solution and solid state, electrochemical properties and X-ray crystal structures.

4,4′-Bibenzo[c]thiophene 4,4′-BBT and its silyl-substituted derivatives 1,1′-Si-4,4′-BBT and 1,1′,3,3′-Si-4,4′-BBT have been designed and developed as new π-building blocks.

Development of 4,4′-bibenzo[c]thiophene fluorophores with substituents on the thiophene rings

We provide a facile synthetic method of 1,1′-disubstituted 4,4′-bibenzo[c]thiophene fluorescent dyes from 1,1′,3,3′-tetrahydro-[4,4′-bibenzo[c]thiophene] 2,2′-dioxide.

Carbazole Substituted BODIPYs

Difluoroboron-dipyrromethenes (BODIPYs) are highly popular fluorescent dyes with applications as NIR probes for bioimaging, fluorescent tags/sensors and as photosensitizers in cancer therapy and organic photovoltaics. This review concentrates on the synthesis and spectral properties of BODIPY dyes conjugated with carbazole heterocycle. The carbazole is an electron rich tricyclic compound and due to its excellent electronic properties, it is extensively used in the production of electroluminescent materials and polymers. This review highlights the recent progress made on the series of BODIPY derivatives containing carbazole ring at alpha, beta, and meso-positions of the BODIPY skeleton. Carbazole based hybrid BODIPYs, carbazole linked aza-BODIPYs and carbazole-fused BODIPYs are also discussed.

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D-π-)2A fluorescent dyes

The donor-acceptor-π-conjugated (D-π-)₂A fluorescent dyes OUY-2, OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as D (electron-donating group)-π (π-conjugated bridge) moiety and a pyridine, pyrazine or triazine ring as electron-withdrawing group (electron-accepting group, A) have been designed and synthesized. The photophysical and electrochemical properties of the three dyes were investigated by photoabsorption and fluorescence spectroscopy, Lippert-Mataga plots, cyclic voltammetry and density functional theory calculations. The photoabsorption maximum (λ_max,abs) and the fluorescence maximum (λ_max,fl) for the intramolecular charge-transfer characteristic band of the (D-π-)₂A fluorescent dyes show bathochromic shifts in the order of OUY-2 < OUK-2 < OUJ-2. Moreover, the photoabsorption bands of the (D-π-)₂A fluorescent dyes are nearly independent of solvent polarity, while the fluorescence bands showed bathochromic shifts with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert-Mataga plots for OUY-2, OUK-2 and OUJ-2 indicate that the Δμ (= μ_e - μ_g) value, which is the difference in the dipole moment of the dye between the excited (μ_e) and the ground (μ_g) states, increases in the order of OUY-2 < OUK-2 < OUJ-2. Therefore, the fact explains our findings that OUJ-2 shows large bathochromic shifts of the fluorescence maxima in polar solvents, as well as the Stokes shift values of OUJ-2 in polar solvents are much larger than those in nonpolar solvents. The cyclic voltammetry of OUY-2, OUK-2 and OUJ-2 demonstrated that there is little difference in the HOMO energy level among the three dyes, but the LUMO energy levels decrease in the order of OUY-2 > OUK-2 > OUJ-2. Consequently, this work reveals that for the (D-π-)₂A fluorescent dyes OUY-2, OUK-2 and OUJ-2 the bathochromic shifts of λ_max,abs and λ_max,fl and the lowering of the LUMO energy level are dependent on the electron-withdrawing ability of the azine ring, which increases in the order of OUY-2 < OUK-2 < OUJ-2.

Solid-state emissive O-BODIPY dyes with bimodal emissions across red and near infrared region

Fluorescent compounds with solid-state emission are expected to have broad applications in the development of optoelectronic devices. In this study, we develop O-BODIPY based fluorescent dyes which exhibit strong bimodal solid-state emissions across red and NIR regions. After one pot synthesis, samples are characterized by X-ray diffraction, cyclic voltammetry, UV-vis absorption, and fluorescence spectra. All the experimental data reveal the multiple excitation and efficient emission features in the aggregation states. Furthermore, the two produced probes can be successfully applied for tracking lysosomes in HeLa cells with low cytotoxicity.

We develop O-BODIPY based fluorescent probes which exhibit strong bimodal solid-state emissions across red and NIR regions, tracking lysosomes in HeLa cells with low cytotoxicity.

Synthesis of carbazole-based BODIPY dimers showing red fluorescence in the solid state

Carbazole-based BODIPY dimers 2a–g were synthesized via direct arylation.

Carbazole-based BODIPYs with ethynyl substituents at the boron center: solid-state excimer fluorescence in the VIS/NIR region

Carbazole-based BODIPYs 1–6 with several different substituents at the boron atom site were synthesized.

Preservation of main-chain conjugation through BODIPY-containing alternating polymers from electronic interactions with side-chain substituents by cardo boron structures

This manuscript describes the synthesis and electronic structures of the modified boron dipyrromethene derivatives containing cardo boron.

Synthesis and Characterization of Far-Red/NIR-Fluorescent BODIPY Dyes, Solid-State Fluorescence, and Application as Fluorescent Tags Attached to Carbon Nano-onions

A series of π-extended distyryl-substituted boron dipyrromethene (BODIPY) derivatives with intense far-red/near-infrared (NIR) fluorescence was synthesized and characterized, with a view to enhance the dye's performance for fluorescence labeling. An enhanced brightness was achieved by the introduction of two methyl substituents in the meso positions on the phenyl group of the BODIPY molecule; these substituents resulted in increased structural rigidity. Solid-state fluorescence was observed for one of the distyryl-substituted BODIPY derivatives. The introduction of a terminal bromo substituent allows for the subsequent immobilization of the BODIPY fluorophore on the surface of carbon nano-onions (CNOs), which leads to potential imaging agents for biological and biomedical applications. The far-red/NIR-fluorescent CNO nanoparticles were characterized by absorption, fluorescence, and Raman spectroscopies, as well as by thermogravimetric analysis, dynamic light scattering, high-resolution transmission electron microscopy, and confocal microscopy.

Strategy to enhance solid-state fluorescence and aggregation-induced emission enhancement effect in pyrimidine boron complexes

The synthesis and the solution/solid-state fluorescence properties of pyrimidine-based monoboron complexes differing in terms of the substituents [either two fluorine atoms (BF2 complex) or two phenyl groups (BPh2 complex)] on the boron atom are reported herein. Unrestricted C-Ar intramolecular rotation in the non-, trifluoromethyl-, and cyano-substituted derivatives resulted in negligible fluorescence in solution. On the other hand, methoxy- and dimethylamino-substituted analogues caused the restriction of the C-Ar intramolecular rotation and consequently resulted in relatively strong fluorescence in solution. The non-, trifluoromethyl-, and cyano-substituted derivatives showed a pronounced aggregation-induced emission enhancement effect. Dimethylamino-substituted derivatives exhibited solvatochromism in the fluorescence spectra. Substitution with BPh2 effectively enhanced the fluorescence quantum yield compared to the corresponding BF2 complexes in the solid-state.

Carbazole substituted boron dipyrromethenes

meso-N-Butylcarbazole substituted BODIPYs showed red shifted emission, large Stokes shifts and efficient energy transfer from the meso-carbazole unit to the BODIPY core.