DOUBLE-PULSE DICHROMATIC PHOTOLYSIS OF FAC-CLRE(CO)3L2 (L = 4-PHENYLPYRIDINE OR 4-CYANOPYRIDINE) - PHOTOHOMOLYSIS OF RE-L BONDS INDUCED BY IRRADIATION OF PHOTOCHEMICALLY UNREACTIVE CHARGE-TRANSFER STATES

Photochemical reactions of fac-ClRe(CO)3L2, L = 4-phenylpyridine or 4-cyanopyridine, were investigated by sequential biphotonic excitations: one laser flash was used for the preparation of the compounds in the lowest lying MLCT {Re --> L} state and another flash for the irradiation of the compounds in such excited state. These photolyses led to photodecompositions into ClRe(CO)3L+ and L.- in a charge-transfer state placed 40 Kk above ground state. Quantum yields determined or various excitation energies show that not all the excited states populated in monophotonic excitations can be reached under the sequential biphotonic regime. Therefore, photogeneration of the biradical intermediate, ClRe(CO)3(L.+)(L.-), from ligand-centered states has not been detected in these experiments. Results from monophotonic and biphotonic excitations have been used for a semiquantitative mapping of the excited-state potential surfaces.