Unravelling the effect of donor-π-acceptor architecture in designing 1,3-indanedione based sensitizers for DSSC applications

Abstract

• 1,3-indanedione-based electron-acceptor group has been employed in designing new sensitizers and theoretical calculations of the nine sensitizers, that are designed based on D-π-A architecture, were performed at DFT and TDDFT level. • HOMO-LUMO energy levels of the designed dyes are matching with the energy levels of titania and redox couples. • Frontier molecular orbital (FMO) analysis revealed intra-molecular charge transfer from the electron-donor to the 1,3-indanedione electron-acceptor. • Two-fold enhancement of dipole moment was observed in all sensitizers upon binding on (TiO 2 ) 9 nanocluster. • The simulated electronic spectra of free dyes and Dye@TiO 2 encompass the entire visible region. • Phenoxazine (POZ) and phenothiazine (PTZ) electron-donor moieties significantly improved the chemical reactivity and photophysical properties and therefore, corresponding RK4 and RK5 sensitizers are better than others. • The D-π-A architecture is found to be better than D-π-A-D architecture in the case of 1,3-indanedione-based sensitizers. Molecular engineering plays a vital role in the design of efficient organic sensitizers for DSSC applications. The study highlights the density functional theory calculations of nine organic sensitizers, designed based on a new 1,3-indanedione electron-acceptor cum anchoring group. The new sensitizers (RK1-9) have been designed by tailoring a modified 1,3-indanedione electron-acceptor with conventional electron-donors in the form of D-π-A architecture. Geometry optimization studies reveal that the RK7 & RK8 molecules have more twisted geometries. Similarly, the RK5 dye has the smallest energy gap of 2.34 eV compared to other dyes. LUMO energy levels of all the designed dyes are positive, found above the conduction band energy level, and the HOMO energy levels were more negative than the redox potentials. Calculated electrochemical parameters suggest that the dyes RK1-5 and RK9 inject the electrons efficiently into the conduction band of TiO 2 . Further, the Gibbs free energies of the dyes indicate that the RK4 and RK5 dyes regenerate much faster than the other dyes. The electronic absorption spectra of the RK dyes were steadily shifting towards the longer wavelength region with solvent polarity and further red-shifts upon adsorbing on the (TiO 2 ) 9 nanocluster. The LUMO and LUMO+1 wave functions of the RK dye@(TiO 2 ) 9 complexes are confined to the (TiO 2 ) 9 nanocluster, suggesting effective intramolecular charge transfer upon photo-excitation. Overall, the computational study demonstrates the significance of the 1,3-indanedione electron-acceptor and o the D-π-A architecture in the molecular design of new organic sensitizers for DSSC applications.