“…This interaction causes the appearance of new SO2 vibrational bands, as reported for several amines where the formation of charge-transfer is verified. [51,52,54] As shown in Fig. 4a, the strongest vibrational frequencies are assigned to C=N, CH2, C-N, and C-H stretching modes at 1654 cm -1 , 1448 cm -1 , 1160 cm -1 and 690 cm -1 , respectively.…”