Quantum Simulation of Carrier Dynamics in Nanographene-fused Carbaporphyrin Tweezers@C60 Heterojunctions: Role of Dihedral Angle Engineering

Abstract

Molecular structures and electronic information of semiconductors are two fundamental concepts in photovoltaic research, as they directly control the charge carrier’s behaviour. We use nonadiabatic (NA) quantum simulation to demonstrate geometry dependent excited state dynamics in nanographene-fused carbaporphyrin tweezers (NCT) and encapsulated C60 by engineering dihedral angle between the nanographene planes. Herein, we investigate that the photoinduced ultrafast electron transfer (ET) occurs at sub-picosecond timescale in dipyrromethene (D)-NCT@C60, well corroborated with the experiment. The simulated average dihedral angle between nanographene planes is 56.73° in D-NCT@C60. We observed that the dihedral angle modelling of the tweezers in aza-dipyrromethene (AD)-NCT@C60 [49.84°] and 2,2-bipyrrole (BP)-NCT@C60 [64.96°] plays a subtle role on the ET. The identical ET pattern aligns with the comparable energy offset and NA coupling values between donor and acceptor states. In contrast, the dihedral angle variation greatly influenced the electron-hole recombination rate at the band edges. In BP-NCT@C60, electrostatic interaction between linker and C60 confines C60 into the tweezer’s cavity, while nanographene-C60 interaction increases the linker-C60 separation in AD-NCT@C60. Also, lower dihedral angle limits energy level reduction of C60 and hindered the conjugation of participating orbitals, widening the band gap. The larger band gap, longer spatial charge separation and weak NA coupling at the band edges suppress the recombination rate in AD-NCT@C60. In this theoretical study, we highlight the impact of dihedral angle on the carrier dynamics of NCT@C60 heterojunctions to achieve efficient photovoltaic device.