A detailed theoretical investigation on intramolecular charge transfer mechanism of primary, secondary, and tertiary p-amino substituted benzaldehyde

Abstract

This article reports a detailed theoretical investigation on dual fluorescence properties of p-amino substituted benzaldehyde molecules by taking specifically p-N,N-dimethylaminobenzaldehyde (3° PABA), p-N-methylaminobenzaldehyde (2° PABA), and p-aminobenzaldehyde (1° PABA) molecules. The calculations are performed in gas phase as well as in butanol (BuOH) and dichloromethane (DCM) solvents. Twisted intramolecular charge transfer emission property is particularly looked at by scanning the potential energy curves as a function of -NR2 (R = H/CH3) rotation (twisting) angle. The results suggest that there are dual emission possibilities for 3° and 2° PABA molecules. Experimental validation is available for the former but not for the latter. 1° PABA, on the other hand, does not show any possibility of dual fluorescence except in BuOH. The theoretical absorption and emission spectra are also calculated and compared with experiment where it is available, and they are in close correlation. Excited state molecular dynamics simulations show that for 3° PABA, the molecule reaches to the 90° twisting angle and stays there with a probability higher than the same probability for 2° PABA. 1° PABA, on the other hand, had showed variations in the twisting angle from 0° to above 100°, but no evidence of this molecule to have considerable lifetime at 90° twisting angle.

Keywords

• TICT
• DFT
• Excited state dynamics