Photoinduced isomerization and luminescence of fac-[Re(CO)3(ph2phen)(bpe)]+

The fac-[Re(CO)3(ph2phen)(trans-bpe)]PF 6 complex, ph2phen = 4,7-diphenyl-1,10-phenanthroline and trans-bpe = trans-1,2-bis(4-pyridyl)ethylene, was synthesized, characterized and its photochemical and photophysical behavior was investigated. This complex exhibits trans->cis photoisomerization of the coordinated trans-bpe ligand. The apparent quantum yields in CH3CN, determined by absorption changes, are phi313 nm = 0.19 ± 0.02, phi365 nm = 0.18 ± 0.04 and phi404 nm = 0.18 ± 0.02. Higher true quantum yields (phi365 nm = 0.40 ± 0.06) were determined by ¹H NMR spectroscopy. The coordination of the trans-bpe ligand to the rhenium(I) polypyridyl complex enables a photosensitized isomerization under a lower energy region irradiation, where the free ligand does not absorb. The increasing luminescence as the photoproduct, fac-[Re(CO)3(ph2phen)(cis-bpe)]+, is formed is ascribed to the change of the lowest lying excited state from ³IL to ³MLCT. The emission exhibits a hypsochromic shift associated with the rigidochromic effect.