Modelling natural dye molecules lawsone and purpurin in different solvents for DSSC applications: a DFT and TD-DFT study.

The solvent effect on the molecular properties of lawsone and purpurin molecules has been investigated using DFT and TD-DFT. The calculations have been performed using CAM-B3LYP functional and 6-311++G(d,p) basis set. Molecular properties including solute energy, electronic spatial extent, HOMO–LUMO energy gap, thermodynamic properties, the free energy of solvation, electronic properties and UV–visible spectra have been studied. These properties have been analysed in 12 solvents, i.e. benzene, chloroform, aniline, dichloromethane, dichloroethane, benzyl alcohol, 3-pentanone, acetone, ethanol, methanol, acetonitrile and DMSO, and the variation of molecular properties has been studied as a function of the dielectric constant of solvents. We also studied the light-harvesting efficiency (LHE) and the lifetime of excitation of dye molecules in the presence of selected solvents to identify its use as a sensitizer in dye-sensitised solar cells. It has been found that purpurin molecule exhibits a higher LHE and lower excited state lifetime than lawsone molecule. We also observed that the LHE of lawsone molecule has a maximum value for aniline and benzyl alcohol solvents, whereas for purpurin molecule, aniline shows greater LHE values due to the auxochrome effect. [ABSTRACT FROM AUTHOR]