Resonance Raman, surface-enhanced resonance Raman, infrared, and ab initio vibrational spectroscopic study of tetraazaannulenes

The IR and resonance Raman spectra of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TAA) and 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TMTAA) have been measured and compared to ab initio calculations of the vibrational wavenumbers, using the 3-21G basis set. An excellent fit is found between the experimental and calculated data, enabling precise vibrational assignments to be made. For the CC and CN stretching vibrations there is substantial separation between the vibrational motion of the diimine and benzene ring parts of the macrocycles. Surface-enhanced Raman spectra were obtained following adsorption on Ag electrodes, with potentials in the range -0.1 to -0.6 V vs Ag/AgCl. The data indicate that both macrocycles adopt either a perpendicular edge-on or tilted orientation on the Ag electrode surface.