Abstract
The time‐resolved Tn←T1 resonance Raman spectra of quinoline (1‐azanaphthalene), isoquinoline (2‐azanaphthalene), quinoxaline (1,4‐diazanaphthalene), and quinazoline (1,3‐diazanaphthalene) molecules in cyclohexane solution are reported, and vibrational assignments and structural implications are discussed. In each of the four compounds, the most resonance enhanced Raman band lies in the 1340–1270 cm−1 region and corresponds to nuclear displacements involving in‐plane stretching motions of the CC and CN bonds. In diazanaphthalenes, drop in the frequency of this vibration on S0 to T1 excitation (97 cm−1 in quinoxaline, 76 cm−1 in quinazoline) is observed to be higher than in azanaphthalenes (31 cm−1 in quinoline, 58 cm−1 in isoquinoline) implying pronounced elongation of the CN bonds, in comparison to the CC bonds, in the T1 states. The T1 Raman spectra of azanaphthalenes, in contrast to naphthalene, are observed to exhibit significant solvent dependency.
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