Vibrationally resolved deep–red circularly polarised luminescence spectra of C70 derivative through Gaussian curvature analysis of ground and excited states

Abstract

Over the last years, the interaction of fullerene with circularly polarized light has attracted growing attention for potential electronic and optical applications. However, in literature there is only one example of fullerene derivative capable of emitting circularly polarized light, showing an active circularly polarized luminescence (CPL) signal in the deep-red visible region. This unique luminophore offered us the possibility to study the connection between the topological features of C70 spheroid and its chiral emission properties. In light of these considerations, we proposed a theoretical protocol that combines three different step: (1) The Ball Pivoting Algorithm for C70 surface reconstruction. (2) The discrete gaussian curvature analysis in the ground (S0) and excited states (S1). (3) The computation of the vibrationally-resolved CPL spectrum. The first step allowed us to extract useful information that linked the topological shape of C70 to the sp2 carbon network chemistry. The DFT benchmark in the second step guided us in grasping the best functional for the C70 curvature simulation in the ground state, spotlighting how B97D3 excellently succeed for this task. The curvature investigation in the first excited state showed that (for all the twenty exchange–correlation functional tested) the C70 fragment is more curved in S1 than in S0. The final step collected the topological information from the previous sections to provide a detailed overview of the theoretical factors (such as the quantum formalism, the potential energy surface description and the transition dipole moment approximation) impacting on the C70 vibrationally resolved CPL spectrum. We found that the adiabatic hessian model coupled with the Franck-Condon Herzberg-Teller approximation computed at PW6B95D3/6-311G(d,p) level provides excellent results in emulating the band-shape and position of the experimental CPL spectrum.