Spectral characteristics of 3,5-diaminobenzoic acid in pure and mixed solvents: Experimental and theoretical study

Abstract

The effect of solvents on the absorption and fluorescence (FL) spectra of 3,5-diaminobenzoic acid (DABA) was explored in pure solvents of diverse polarities and hydrogen bonding abilities. A bathochromic shift was observed in FL spectra while moving from non-polar to polar aprotic/protic solvents. The solvatochromic-based approaches showed that the dipole moment of DABA in the excited state (ES) is higher than its ground state (GS), which signifies that the ES is more polarized, corresponding to the GS. Moreover, the Catalan solvent polarity scale analysis suggested that the solvent acidity (SA) and dipolarity (SdP) influenced the absorption and FL spectra of DABA in solvents, signifying the presence of non-specific and specific interactions. The FL decay analysis in solvents was correlated with the observed steady-state results and suggested the presence of intramolecular charge transfer (ICT). The preferential solvation concept was utilized to understand the spectral variations of DABA in MeOH-water and DMSO-water mixtures. Further, the computational calculations utilizing the DFT (density functional theory) and TD-DFT (its time extension) for DABA were performed in the gas phase and solvents to estimate the electronic transitions and dipole moments. Furthermore, the natural bond orbital analysis and non-linear optical parameters were also obtained by DFT, and the findings revealed that ICT stabilizes the molecular system. Thus, DABA may have potential applications in the field of optoelectronics and fluorescence sensing.