Indole-based Dyes Research Articles

Identification of novel indole-based dyes as active photo-sensitizers: Synthesis, photophysical, electrochemical and computational investigation

Novel D–π–A type indole-based compounds have been designed and synthesized as active photosensitizers for dye-sensitized solar cells (DSSCs). The molecular structures of indole-based compounds were identified and characterized using IR, NMR, and HRMS spectra data. The attributes of the indole-based compounds were evaluated in terms of their optical, electrochemical, light-harvesting efficiency (LHE), HOMO/LUMO level and redox behaviour. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were conducted to disclose the electronic and optical attributes of novel indole-based compounds. All the compounds revealed well-defined absorption with elevated absorptivity and a small band gap (2.89–3.01 eV). The HOMO to LUMO energy transfer percentage obtained from TD-DFT, for the synthesized compounds is in the range of 86%–99%. The projected light-harvesting efficiency (LHE) for the indole-based compounds is between 0.371 and 0.666. The greatest open circuit voltage (Voc) value was found in the methoxyphenyl-substituted indole-based compound, which is advantageous for DSSCs to obtain external maximum power output.

Development of Highly Fluorogenic Styrene Probes for Visualizing RNA in Live Cells.

Styrene dyes are useful imaging probes and fluorescent sensors due to their strong fluorogenic responses to environmental changes or binding macromolecules. Previously, indole-containing styrene dyes have been reported to selectively bind RNA in the nucleolus and cytoplasm. However, the application of these indole-based dyes in cell imaging is limited by their moderate fluorescence enhancement and quantum yields, as well as relatively high background associated with these green-emitting dyes. In this work, we have investigated the positional and electronic effects of the electron donor by generating regioisomeric and isosteric analogues of the indole ring. Select probes exhibited large Stokes shifts, enhanced molar extinction coefficients, and bathochromic shifts in their absorption and fluorescence wavelengths. In particular, the indolizine analogues displayed high membrane permeability, strong fluorogenic responses upon binding RNA, compatibility with fluorescence lifetime imaging microscopy (FLIM), low cytotoxicity, and excellent photostability. These indolizine dyes not only give rise to rapid, sensitive, and intense staining of nucleoli in live cells but can also resolve subnucleolar structures enabling highly detailed studies of nucleolar morphology. Furthermore, our dyes can partition into RNA coacervates and resolve the formation of multiphase complex coacervate droplets. These indolizine-containing styrene probes offer the highest fluorescence enhancement among the RNA-selective dyes reported in the literature; thus, these new dyes are excellent alternatives to the commercially available RNA dye, SYTO RNASelect, for visualizing RNA in live cells and in vitro.

Effect of donor and acceptor end-groups on electronic structure and spectral-fluorescent properties of merocyanines in frozen ethanol

UV–vis absorption and fluorescence spectra of a series of merocyanines with varying heterocyclic donor and carbonyl-comprising acceptor groups have been studied in frozen ethanol at 77 K. Due to a greater polarity of a frozen solvent matrix in comparison with the liquid solvent, the electronic structure of donor–π–acceptor molecules in the former becomes much more dipolar. The resulting spectral effects depend on the donor–acceptor abilities of the terminal groups. In the case of positively solvatochromic indole-based dyes comprising the 1,3-indandione or barbituric acceptors, going from 293 to 77 K results in a narrowing and bathochromic shifts of absorption bands. Vice versa, for more dipolar reversely and negatively solvatochromic merocyanines comprising the thiobarbituric acceptor-group, the solvent freezing leads to a broadening and hypsochromic shifts of the absorption bands, which is very unique, taking into account that the solute vibrations/rotations should decrease in a frozen solvent. In all cases, the fluorescence bands are shifted hypsochromically at cryo-temperature and are closely mirror-like to the absorption ones, which, along with the smaller Stokes shifts, has been explained by the inhibited solvent rearrangement in the frozen matrix, resulting in a greater similarity of the ground state S0 and the fluorescent excited state S1. The deductions about the electronic structure of the studied dyes in the ground and excited states and its dependence on the donor–acceptor properties of the end-groups correlate well with the results of the PCM/(TD)-DFT calculations performed within the four-level diagram of electronic transitions.

Synthesis and photovoltaic properties of new thieno[3,2-b]indole-based dyes

New dyes of the 3-[5-(4-alkyl-4H-thieno[3,2-b]indol-2-yl)thiophen-2-yl]-2-cyanoacrylic acid series were prepared based on 2-(thien-2-yl)-substituted thieno[3,2-b]indole by its sequential N-alkylation, formylation, and condensation of the resulting aldehydes with cyanoacetic acid. The possible application of these dyes as sensitizers of mesoporous titanium dioxide thin films in dye-sensitized solar cells (DSSC) was shown. It was established that the efficiency of DSSC based on the dye IS 4 is superior to that of a similar element based on the commercial dye N3 [cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(ii)].

Synthesis, optical and electrochemical properties of new thieno[2,3-b]indole-based dyes

Synthesis, optical and electrochemical properties of new thieno[2,3-b]indole-based dyes

Novel push-pull thieno[2,3-b]indole-based dyes for efficient dye-sensitized solar cells (DSSCs)

Novel push-pull thieno[2,3-b]indole-based dyes for efficient dye-sensitized solar cells (DSSCs)

Thieno[2,3-b]indole-based organic dyes for dye-sensitized solar cells: Effect of π-linker on the performance of isolated dye and interface between dyes and TiO2

A series of novel D-π-A type organic dyes with different π-linker are theoretically designed and investigated for their potential applications in dye-sensitized solar cells (DSSCs). We mainly focused on the influence of the extension of π-linker on the overall efficiency. The discussions are classified into two aspects: one is the isolated dyes and the other is the dye-TiO2 system. The calculated results indicate that the isolated dyes THI-2T-C, THI-4T-3C, and THI-6T-5C have the better overall efficiency. Further, the THI-4T-3C and THI-5T-4C have the acceptable performance if the dye-TiO2 system is considered. Combination of the isolated and the adsorbed systems, the THI-4T-3C with the moderate π-linker is considered to be more suitable choice for thieno[2,3-b]indole-based dyes rather than the longest π-linker.

Organic Dyes Containing Thieno[3,2-b]indole Donor for Efficient Dye-Sensitized Solar Cells

Three new organic dyes, comprising thieno[3,2-b]indole moiety as an electron donor, n-hexyl substituted oligothiophene units as a π-conjugated bridge, and cyanoacrylic acid group as an electron acceptor and anchoring group, have been designed and synthesized for nanocrystalline TiO2 dye-sensitized solar cells (DSSCs). Compared with our previous carbazole-based MK dyes, in the similar donor-π-acceptor structure, thieno[3,2-b]indole not only has stronger electron donating ability but also could hold the dye molecule in a more planar conformation than carbazole. The newly synthesized thieno[3,2-b]indole-based dyes exhibit their major electronic absorption in the range of 400−600 nm in the visible region in solution. Solar energy to electricity conversion efficiency (η) up to 7.8% was obtained with a DSSC using 2-cyano-3-[5′′-(4-ethyl-4H-thieno[3,2-b]indol-2-yl)-3′,3′′,4-tri-n-hexyl-[2,2′,5′,2′′]terthiophen-5-yl]acrylic acid (MKZ-40) as light harvesting sensitizer under simulated AM 1.5 G irradiation (100 mW cm−2) with an aperture mask: short-circuit photocurrent density (Jsc) = 14.6 mA cm−2, open-circuit voltage (Voc) = 0.70 V, and fill factor (FF) = 0.76, suggesting that thieno[3,2-b]indole-based organic dyes are promising candidates for DSSCs. However, the DSSCs based on thieno[3,2-b]indole dyes showed shorter electron lifetime compared to that for the solar cell with a conventional carbazole dye, resulting in lower Voc.