A promising small-sized near-infrared absorbing zwitterionic dye for DSSC and NLO applications: DFT and TD-DFT approaches

Herein we investigate three quinoid zwitterionic dye sensitizers having donor-donor (4-dimethylaniline; ZIDM), donor-acceptor (4-dimethylaniline and 4-benzoic acid; ZIMCA), and acceptor-acceptor (4-benzoic acid; ZIDCA) that can be used in dye sensitized-solar cells and non-linear optical (NLO) application through density-functional theory (DFT) and time-dependent-DFT computations. ZIDM showed better charge transfer than ZIMCA and ZIDCA, which showed similar trends in chemical potential, electrophilicity index, hardness, and hyperhardness. The higher values of open circuit voltage, light harvesting efficiency, lower binding, and adsorption energy values for the dye to bind with the TiO₂ cluster were observed for ZIDM. The results suggest that these dyes can easily hold with the TiO₂ cluster through the monodentate binding mode possible between Ti and oxygen of the zwitterionic backbone. The examination of the linear and NLO properties of these dyes revealed that ZIDM has a higher α₀ = 80.64 × 10^-24 esu, β₀ = 448.54 × 10^-30 esu, and γ = 2219.23 × 10^-36 esu in DCM. Similarly, higher values of molecular hyperpolarizability of 1335.0 × 10^-48 esu and 8818.3 × 10^-48 esu were observed in gas and DCM for ZIDM than ZIMCA and ZIDCA.