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 rotationa l resolution has been used to probe the changes in energy, electronic distribution, and geometry that occur when 1-aminonaphthalene (1AN) ab sorbs light at similar to 332 nm. The 0(0)(0) band of the S-1<--S-0 tr ansition of 1AN is red shifted by nearly 2000 cm(-1) with respect to t he corresponding band of naphthalene. Additionally, it is mainly b-axi s polarized, unlike the corresponding bands of naphthalene and other. 1-substituted naphthalenes. Thus, (1)L(a)/(1)L(b) State reversal occur s 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 ban ds in the S-1<--S-0 transition exhibit significantly different rotatio nal constants, inertial defects, and transition moment orientations. A n explanation for these findings is given that is based on the well-kn own conjugative properties of the NH2 group in chemically related syst ems. (C) 1996 American Institute of Physics.