Time-Resolved Resonance Raman and Density Functional Study of the Radical Cation of Promazine

Abstract

We present a resonance Raman spectrum of the radical cation of promazine. Density functional theory computations were used to find the structures, hyperfme coupling constants (hfcc's), spin densities, and vibrational frequencies for the ground electronic states of the neutral promazine molecule and its radical cation. Preliminary assignments for all of the observed Raman bands for the neutral promazine molecule and its radical cation are given. The density functional theory computed optimized structures show the S0 states of the neutral molecule (with a dihedral angle of 147.1°) and its radical cation (with a dihedral angle of 172.13°) are both nonplanar. The DFT-computed spin densities suggest the radical cation of promazine has significantly more spin density on nitrogen compared to sulfur, while the sulfur has a greater spin density than nitrogen in the radical cation of phenothiazine. The calculated HOMO and LUMO electron densities display noticeable differences in both the central ring and the side chain upon excitation. This appears consistent with the promazine radical cation experimental resonance Raman intensities.