EXCITED-STATE PROPERTIES OF PLATINUM(II) COMPLEXES CONTAINING BIPHENYL AS A LIGAND - COMPLEXES OF THE TYPE [(BPH)PTL2], WHERE L = MONODENTATE OR SATURATED BIDENTATE LIGANDS

The preparation, physical properties, and photophysical properties of [Pt(bph)(C2H5)2S]2, [Pt(bph)(CH3CN)2], [Pt(bph)(en)], and [Pt(bph)(py)2], where bph2- is the dianion of biphenyl, en is ethylenediamine, and py is pyridine, are described. The complexes display d-pi --> pi* transitions in the 300-400-nm region and intraligand pi --> pi* transitions at higher energy. Only one redox process, an irreversible oxidation, is observed in the +2 to -2 V region. The E1/2 values range from 0.67 to 1.35 V vs SSCE. Highly structured emission is observed and attributed to a 3LC --> 1GS process. Spectral curve fitting using a four-mode fit gives E00 congruent-to 20 670 cm-1 and vibrational frequencies of 1550, 1150, 715, and 375 cm-1 that are nearly independent of the specific complex. Temperature-dependent lifetime data reveal the presence of an energy level above the 3LC state with an activation energy of 1220 cm-1 for [Pt(bph)(CH3CN)2], 2280 cm-1 for [Pt(bph)(py)2], and 2490 cm-1 for [Pt(bph)(en)]. The energy gap of approximately 2.6 eV gives rise to high oxidative quenching power (-1.14 to -1.71 V) demonstrated by electron-transfer quenching with methyl viologen and o-nitrobenzene.