Abstract
It is well-known that pi-conjugation plays an important role to tune the nonlinear optical (NLO) response of donor-pi-conjugated-acceptor compounds. Fullerenes (C-60) are one of a few compounds who are abounded with pi-conjugation and perhaps are the largest pi-conjugation compounds. In the present study, we systematically designed C-60 derivatives (2 (fulleropyrrolidine) and 2a-2c (fulleropyrrolidine tetrathiafulvalene derivatives where 2a, 2b and 2c are with n = 0, n = 1 and n = 2) through the use of pyrrolidine and tetrathiafulvalene moieties. We applied density functional theory (DFT) methods to calculate their respective geometrical structures, electronic properties, linear and nonlinear optical response properties along with their respective UV-Visible spectra using CAM-B3LYP functional and 6-31G* basis set. The isotropic polarizability (alpha(iso)) and anisotropic polarizability (alpha(aniso)) of 2c was found to be 131.52 x 10(-24) and 47.01 x 10(-24) esu, respectively. Amongst our designed compounds, the maximum second-order nonlinear optical polarizability amplitude (beta(//)) of 2c was found to be 15.69 x 10(-30) esu. Interestingly, 2c shows the highest third-order nonlinear polarizability amplitude of 284.29 x 10(-36) esu that is about three times higher than parent compound 1. Additionally, frontier molecular orbitals (FMOs), molecular electrostatic potential maps (MEPs), transition density matrix (TDM) analysis indicate more effective charge redistribution from donor moiety to acceptor fragments. The density of states (DOS) diagrams reveal distinct electronic contributions of various fragments in the formation of HOMO and LUMO orbitals resulting in efficient intramolecular charge transfer (ICT) and robust third-order NLO response properties of functionalized fullerene derivatives. The current study may arouse the attention of the scientific society to utilize the extensive pi-conjugation of functionalized fullerenes for designing efficient NLO materials.