EXCITE STATE SPECTRA OF 5,15 BISETHYNYL 10,20 DIPHENYL & 10,20 DIPHENYL COMPLEX

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Photoexcitation of [5, 10, 15, 20-tetraphenylporphinato]copper(II) {CuTPP} is typically accompanied by very efficient intersystem crossing (< 10 ps) of the sing-doublet to the trip-doublet and trip-quartet manifold through interaction with the paramagnetic d9 copper center. Recent transient resonance Raman investigations of related compounds [5,15-bis[(4'-nitrophenyl)ethynyl] -10,20-diphenylporphinato] -copper(II) {I} and electronically asymmetric [5-[[4'-(dimethylamino)phenyl]ethynyl] -15-[(4"-nitrophenyl)ethynyl]-10,20-diphenylporphinato]-copper (II) {II} reveal excited state spectra consistent with substantial electron transfer (ET) from the porphyrin macrocycle to the nitro moiety as displayed by 20 cm-1 downshifts of the N-O stretching frequency. Unlike the 30 mW laser power transient resonance Raman spectrum of CuTPP which shows features consistent with both excited and ground state contributions, the spectra of both I and II show no detectable ground state contributions even when examined at 4% of the laser power employed in the CuTPP experiment. The observed bleaching of the ground state in I and II is consistent with a relatively long-lived excited state. To elucidate the excited state dynamics of these compounds, we propose performing triplet-triplet transient absorption and phosphorescent lifetime measurements of I and II as well as the unsubstituted compound, [5,15-bis[(phenyl)ethynyl]-10,20-diphenylporphinato]copper(II), as well as the zinc analogs of these three compounds. (These results have been published in J. Amer. Chem. Soc. 119, 12578 (1997).)