High resolution electronic spectroscopy of 1-aminonaphthalene: S-0 and S-1 geometries and S-1<-S-0 transition moment orientations

Fluorescence excitation spectroscopy at both vibrational and rotational resolution has been used to probe the changes in energy, electronic distribution, and geometry that occur when 1-aminonaphthalene (1AN) absorbs light at similar to 332 nm. The 0(0)(0) band of the S-1<--S-0 transition of 1AN is red shifted by nearly 2000 cm(-1) with respect to the corresponding band of naphthalene. Additionally, it is mainly b-axis polarized, unlike the corresponding bands of naphthalene and other. 1-substituted naphthalenes. Thus, (1)L(a)/(1)L(b) State reversal occurs on 1-substitution of naphthalene with an NH2 group. The S-0 state of 1AN is pyramidally distorted at the nitrogen atom. Additionally, the NH2 group is rotated by similar to 20 degrees about the C-NM(2) bond. Excitation of 1AN to the zero-point vibrational level of its S-1 state reduces the C-NH2 bond length by similar to 0.2 Angstrom and flattens the NH2 group along both out-of-plane coordinates. Other vibronic bands in the S-1<--S-0 transition exhibit significantly different rotational constants, inertial defects, and transition moment orientations. An explanation for these findings is given that is based on the well-known conjugative properties of the NH2 group in chemically related systems. (C) 1996 American Institute of Physics.