The investigation of the ultrafast excited state deactivation mechanisms for coumarin 307 in different solvents

The intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) processes of coumarin 307 (C307) in different solvents were investigated by performing steady-state/time-resolved transient absorption spectroscopic and steady-state photoluminescence spectroscopic characterizations in combination with time-dependent density functional theoretical calculation (TDDFT). The study unveiled the remarkable influence of solvent polarity and the strength of intermolecular hydrogen bonds formed between the solutes and solvents on the relaxation dynamics of the electronic excited state. Significantly, the emergence of the TICT state was observed in polar solvents, specifically dimethylformamide (DMF) and dimethyl sulfoxidemethanol (DMSO), owing to their inherent polarity as well as the enhanced intermolecular hydrogen bonding interactions. Interestingly, even in a weak polar solvent such as methanol (MeOH), the TICT state was also observed due to the intensified hydrogen bonding effects. Conversely, nonpolar solvents, exemplified by 1,4-dioxane (Diox), resulted in the stabilization of the ICT state due to the augmented N-H⋯O hydrogen bonding interactions. The experimental findings were corroborated by the computational calculations, thus ensuring the reliability of the conclusions drawn. Furthermore, schematic diagrams were presented to illustrate the mechanisms underlying the excited-state deactivation. Overall, this investigation contributes valuable mechanistic insights and provides a comprehensive understanding of the photochemical and photophysical properties exhibited by coumarin dyes.

Hopping transport in triphenylamine and indoline based semiconductors in the context of dye sensitized solar cells: A DFT Study

Dye-sensitized solar cells (DSSCs) have drawn a significant interest due to their low production cost, light weight, better flexibility in design, and better tunability. Herein, two metal free organic dyes based on donor-π-acceptor (D-π-A) type architecture having methoxy substituted triphenyl amine (TPA) and methyl substituted indoline(IND) as the donor units, cyanoacrylic acid (CA) as the acceptor unit, and 8H-thieno [2^', 3^':4,5]thieno[3,2-b]thieno[2,3-d]pyrrole (TTP) unit as π-bridge are successfully designed for fabrication of DSSCs. To tune the optical properties, structural engineering has been carried out at the TTP unit via substituting different +I groups, viz., -H, -CH₃, -OCH₃, -CH₂CH₂, -SH, and -OH and different -I groups viz. -CF₃, -COCH₃, -COOH and -CN. Various structural, electronic and optical parameters are calculated for the designed dyes. Our study reveals that dyes substituted with electron withdrawing groups possess lower Δ_H-L values for both TPA-CA and IND-CA groups of dyes. Moreover, the ESOP and GSOP values of all the dyes confirm the spontaneity of the electron injection and dye regeneration processes with respect to the conduction band of the TiO₂ surface and redox potential of the I^-/I₃^- redox couple. The absorption properties also manifest the red shift behavior of the designed dyes. Further, from the study of the structural and electronic properties of the dye-Ti₅O₁₀ clusters it is evident that the performance of the dyes get increased upon binding to the TiO₂ surface. Hence, our study provides a good recommendation for further designing of dyes to enhance the performance of DSSCs.

Synthesis and characterization of novel biological tetracoumarin derivatives bearing ether moieties

A series of novel tetracoumarin derivatives (3a-f) were prepared using the reaction of ether functionalized dibenzaldehyde with 4-hydroxycoumarin in the presence of sodium acetate. The structure of compounds was validated by IR, NMR, and CHN analyzes. Antimicrobial (antibacterial and antifungal) activity was studied on the basis of the minimum bactericidal concentration, minimum inhibitory concentration and inhibitory zone diameter. Favorable biological activity was found in compound 3f.

Perylenediimides as more than just non-fullerene acceptors: versatile components in organic, hybrid and perovskite solar cells

The most recent advances in the incorporation of perylenediimides in photovoltaic devices are highlighted.

Theoretical Study of the Effect of Different π Bridges Including an Azomethine Group in Triphenylamine-Based Dye for Dye-Sensitized Solar Cells

Ten molecules were theoretically calculated and studied through density functional theory with the M06 density functional and the 6-31G(d) basis set. The molecular systems have potential applications as sensitizers for dye-sensitized solar cells. Three molecules were taken from the literature, and seven are proposals inspired in the above, including the azomethine group in the π-bridge expecting a better charge transfer. These molecular structures are composed of triphenylamine (donor part); different combinations of azomethine, thiophene, and benzene derivatives (π-bridge); and cyanoacrylic acid (acceptor part). This study focused on the effect that the azomethine group caused on the π-bridge. Ground-state geometry optimization, the highest occupied molecular orbital, the lowest unoccupied molecular orbital, and their energy levels were obtained and analyzed. Absorption wavelengths, oscillator strengths, and electron transitions were obtained via time-dependent density functional theory using the M06-2X density functional and the 6-31G(d) basis set. The free energy of electron injection (ΔGinj) was calculated and analyzed. As an important part of this study, chemical reactivity parameters are discussed, such as chemical hardness, electrodonating power, electroaccepting power, and electrophilicity index. In conclusion, the inclusion of azomethine in the π-bridge improved the charge transfer and the electronic properties of triphenylamine-based dyes.

An instantaneous fluorescent probe for detecting hydrogen sulfide in biological systems

An instantaneous (within seconds) fluorescent probe for detecting H₂S was developed and successfully used for H₂S imaging in living cells and zebrafish.

Effect of donor modification on the photo-physical and photo-voltaic properties of N-alkyl/aryl amine based chromophores

Six push–pull sensitizers (MD1 to MD6) having rhodanine-3-acetic acid acting as an electron withdrawing group and N-alkyl/aryl amine as a donor moiety were planned and prepared to rationalize the influence of donor alteration on absorption/emission properties and photon to current conversion efficiency (η).

Design and Synthesis of Coumarin-Imidazole Hybrid Chromophores: Solvatochromism, Acidochromism and Nonlinear Optical Properties

A set of linear and asymmetric coumarin-imidazole hybrid compounds having a N,N-diethylamine at 7-position and imidazole at 3-position on the coumarin were synthesized. Insertion of thiophene π-spacer between coumarin and imidazole moieties (5b, 5d) leads to redshifted absorption and emission compared to 5a and 5c. All the compounds show a noticeable response to trifluoroacetic acid with a redshifted absorption and an increase in emission intensity by twofold. The ratio of ground and excited state acidity constant was calculated using Förster energy cycle, and the ratios were found to be 0.25, 0.96, 0.52 and 1.87, respectively, for 5a-5d. Due to the thiophene π-spacer, elongation of π-conjugation in 5b and 5d leads to high values of polarizability (α), first-order hyperpolarizability (β) and second-order hyperpolarizability (γ). Compound 5b exhibits a high value (895 GM) of two-photon absorption cross section (σ2PA), measured using two-level model.

Synthesis and organic solar cell performance of BODIPY and coumarin functionalized SWCNTs or graphene oxide nanomaterials

Organic solar cell performances of the nanomaterials based on rGO or SWCNTs functionalized by BODIPY or coumarin groups have been investigated.