EXCITED-STATE STRUCTURE AND VIBRATIONS OF P-DIAMINOBENZENE STUDIED BYAB-INITIO CALCULATIONS

The structures and vibrations of p-diaminobenzene (PDAB) in the S-0 an d S-1 states have been studied by ab initio quantum-chemical calculati ons. Results from geometry optimization show that the two stable cis a nd trans conformers of PDAB an nonplanar in the S-0 state. Upon electr onic excitation to the S-1 state, enhanced interaction between the rin g and the amino substituent causes the molecule to become planar and c ontract along the long in-plane axis. A detailed analysis of the norma l vibrations of PDAB in both states has been done on the basis of the motions of individual atoms as well as reduced masses, force constants and frequencies. The computed frequencies are in reasonably good agre ement with the available experimental data. (C) 1998 Elsevier Science B.V. All rights reserved.