Investigation of Aggregation Induced Emission Mechanism of Tetrabenzoheptafulvalene Derivative by Spin-Flip Time-Dependent Density Functional Theory (SF-TDDFT).

Abstract

This study explores the mechanism of aggregation-induced emission (AIE) in the tetrabenzoheptafulvalene derivative, 10,10',11,11'-tetrahydro-5,5'-bidibenzo[a,d][7]annulenylidene (abbreviated as THBDBA) in tetrahydrofuran (THF) solution. We adopted spin-flip time-dependent density functional theory (SF-TDDFT), widely acknowledged for its ability to locate the conical intersection (CI) in medium to large-sized molecules. The strategies used are the excited-state deactivation processes by taking into account the S1/S0 surface-crossing, referred to as the 'minimum energy conical intersection' (MECI). Reduction of oscillator strength (f) near the minimum energy gap (MEG) or CI is also another parameter used to study fluorescence quenching. For the monomer, our findings reveal a significant reduction in f-value for de-excitation near the MEG and CI, signifying that in solution the flapping motion of the phenyl rings plays a vital role to reach the CI. A dimer system is chosen to represent the aggregate state in a smaller scale. The higher energy gap and f-value at MEG with just the dimer system indicates that in the actual aggregate, because of much higher steric and electrostatic confinements the MECI might be absent. This is because the flapping motion of the phenyl rings will be highly restricted thereby favoring radiative transitions for energy dissipation in aggregates or crystals.