7641Coulomb interaction, which consequently is regarded as the origin of the semiconducting gap.The intramolecular transitions were assigned with the aid of the solution spectra of sandwiched phthalocyanines. We found a tendency that upon increasing the degree of oxidation of Pc ring the intensity of the Q-band decreases while that of the neighboring band on the higher wavenumber side increases. This systematic change strongly supports our assignment. On this basis we confidently propose that this latter band can be used as a diagnosis of the ring oxidation. Acknowledgment.We are indebted to Dr. A. Kawamoto of IMS for writing the computer program of the laboratory-made microspectrophotometer in IMS.We report spectroscopic and photophysical data of para-substituted phenylterpyridine (ptpy) Ru (I1) complexes and molecular orbital studies of the Fe(II), Ru(II), and Os(I1) compounds [ M ( R -~t p y )~]~+ , R = H, CH3, OH, OCH3, and CI. The visible charge-transfer absorption of the [R~(R-ptpy)~]~+ is almost twice as intense as observed for the corresponding 2,2'-bipyridine (bpy) complex [Ru(bpy),]*+, and it is red shifted by about 50 nm. The luminescence in solution and in membranes (Nation, cellophane)is very weak at room temperature, and the luminescence decay time is on the order of a few nanoseconds. In a glass at 77 K, however, the luminescence quantum yield is 0.4 and the decay time 13 ps. Excited-state absorption spectra measured at room temperature by laser flash spectroscopy support the interpretation that the first excited state is of the MLCT type. The similarity of the excited-state absorptions to those of the ligand radical anions strengthens the idea that the excited electron is localized on a single ligand. Molecular orbital studies indicate that the nonplanar ligand becomes planar in states corresponding to the (n)I(r*)l and the (r)l(x*)l excited configurations and in the MLCT state of the complex. The same holds for the ligand radical anion. Low-lying d states in the [Fe(R-ptpy)2]Z+ complexes provide efficient relaxation channels by internal conversion. In the Ru(I1) and even more pronounced in the Os(l1) complexes, these states lie far above the MLCT state and can be neglected. Thus the low luminescence quantum yield at room temperature is due to low-energy intramolecular vibrations of the nonrigid complex and not to the coupling with d states. Lowering the temperature results in freezing these intramolecular movements and hence in significantly increasing the luminescence quantum yield. The molecular orbital studies indicate that it is reasonable to describe the MLCT state as [(L)RU~~~(L'-)]~+ because the perpendicular conformation of the two ligands causes all r orbitals to be accidentally 2-fold degenerate and therefore a small asymmetric distortion is sufficient to favor the localized situation.
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