Ab initio/density functional study of vibrational frequencies of acridine in the ground and excited states

The optimized structures and Raman vibrational frequencies of acridine-d(0) and (per-deuterated) acridine-d(9) in the ground (S-0), lowest triplet (T-1), lowest excited singlet (S-1), and anion radical states have been calculated using the B3LYP, HF or CIS method. The calculated frequencies are compared with the available experimental Raman or absorption data. The B3LYP/6-31G* frequencies for the S-0, T-1 and anion radical states and the CIS/6-31G* frequencies for the S-1 state are as a whole in agreement with the experimental data. Some rather large deviations between the predicted and experimental frequencies for the alternately stretching mode of both outer rings (mode A) are pointed out and discussed. The frequencies by using the CIS method for one of the excited triplet states (T-4) have been also calculated to predict the extra resonance signal of the resonance CSRS in the T-1 state for the T-n <-- T-1 resonant condition. The predicted mode which correspond to the experimental ER signals both for acridine-d(0) and -d(9) are assigned to mode A. (C) 2001 Elsevier Science B.V. All rights reserved.