All TD-DFT 39 calculations were performed using the ORCA software (version 5.0.4). Geometry optimizations with tight convergence criteria were done using the long-range corrected CAM-B3LYP hybrid functional and the 6-31G* basis set, in combination with the DFT-D3 empirical dispersion correction with Becke-Johnson damping. The same level of theory has been adopted in other studies on pyrene excimer. Vibrational frequencies were calculated for the relaxed conformers in the S1 state, using the default displacement of ±0.005 atomic units for each coordinate and requiring tight SCF convergence on each displaced geometry. A temperature of 298.15 K was considered for thermochemical analysis.