A bisterpyridine complex of ruthenium(II) (Ru(tpy)2 2+) has been prepared in zeolite Y supercages and investigated by electronic absorption, electronic emission, and resonance Raman spectroscopy. In free solution this complex is practically nonluminescent, having a very short excited-state lifetime (250 ps) at room temperature. However, entrapment within the zeolite supercage results in dramatic increases in emission intensity and excited-state lifetime (140 ns) at room temperature. The observed temperature dependence of the excited-state lifetime has been modeled by a kinetic equation with two thermal terms corresponding to the so-called fourth 3MLCT state and ligand-field state (LF), respectively. It is shown that the increased lifetime of the entrapped complex results from zeolite-induced destabilization of the LF state, a conclusion which is in agreement with results obtained for a number of other zeolite-entrapped ruthenium(II) polypyridine complexes.

Resonance Raman (RR) spectra are reported for dimeric, trimeric, and tetrameric porphyrin arrays in which the porphyrins are directly linked at the meso position. The RR spectra of two monomeric building blocks of the arrays are also examined. The close proximity and orthogonal orientation of adjacent porphyrins in the arrays result in exceptionally strong excitonic interactions along the axis defined by the meso,meso-linkage-(s) and negligible interactions along the orthogonal axis. The coupling scheme breaks the degeneracy of the B excited state and leads to two B(0,0) absorption features. One feature, designated B X (0,0), is the supermolecule absorption that is strongly red-shifted, due to exciton coupling. The other feature, designated B y (0,0), is the superposition of absorptions of the orthogonal, individual porphyrins. This latter absorption occurs at approximately the same energy as the B(0,0) band of a monomeric porphyrin, due to the absence of excitonic interactions. The exciton coupling in the Q state is much weaker than that in the B state, due to the smaller oscillator strength of the former transition. The B-state excitation RR spectra of the meso,meso-linked arrays exhibit a complex and unusual scattering pattern. The most striking features are (1) the appearance of only polarized and anomalously polarized modes in the RR spectrum, (2) the intensity enhancement of anomalously polarized vibrations with B-state excitation, and (3) the large differential enhancement of symmetric versus nontotally symmetric vibrations with excitation across the B-state absorptions. All of these scattering characteristics are due to the effects of symmetry lowering. The asymmetric meso substitution pattern inherent to the meso,meso-linked arrays contributes to symmetry lowering in both the ground and excited electronic states. The strong uniaxial excitonic interactions make an additional contribution to symmetry lowering in the excited state(s). This latter characteristic promotes novel Franck-Condon and vibronic scattering mechanisms in the B state(s) of the arrays. Collectively, the studies of the meso,meso-linked arrays provide insight into the type of RR scattering that might be anticipated for other types of systems that exhibit strong excitonic interactions among the constituents. † Part of the special issue "Thomas Spiro Festschrift". Dedicated to Thomas G. Spiro on the occasion of his 65th birthday.

Resonance Raman (RR) and time-resolved resonance Raman (TR3) spectra are reported for the complexes of divalent ruthenium with the ligands 4,4º-bipyrimidine (bpm) and 2,2º-bipyridine (bpy), i.e. and Ru(bpm) 3 2' Ground-state RR studies of the latter employing excitation with radiation of 413.1, 457.9 and Ru(bpy) 2 (bpm)2'. 514.5 nm permit the assignment of an electronic absorption band maximizing at 428.5 nm to a Ru(II)-to-bpy charge-transfer transition, while the band maximum at 516.0 nm is assigned to the Ru(II)-to-bpm charge-transfer band. The TR3 studies employing the 354.7 nm harmonic of a 10 ns pulsed Nd : YAG laser provide deÐnitive evidence for selective population of the bpm-localized excited state for the heteroleptic complex Ru(bpy) 2 (bpm)2'.

The heteroleptic ruthenium(II) complex Ru(bpy)(2)(dpp)(2+) (where bpy = 2,2'-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) has been prepared in the supercages of Y-zeolite and characterized by diffuse reflectance, electronic absorption, electronic emission, and resonance Raman (RR) spectroscopy, as well as lifetime measurements. The spectral results confirm the identity of the entrapped complex. The diffuse reflectance spectrum of the zeolite-entrapped complex is slightly red-shifted in the visible region compared to the absorption spectrum of the free complex in water solution. The emission maximum for the zeolite-entrapped complex is red-shifted by 16 nm with respect to the complex in water solution and by 38 nm relative to the complex in acetonitrile solution. The emission maximum for a zeolite surface-adsorbed complex is blue-shifted by 12 nm with respect to the complex in water solution, but the emission maxima of the liberated complex after dissolution of the zeolite matrix, for both the entrapped and adsorbed complexes, are identical to the spectrum of the free complex in water solution. There are moderate RR frequency shifts observed for the zeolite-entrapped complex relative to the solution-phase complex as a consequence of the interaction of the complex with the zeolite framework. The excited state lifetime measurement shows no dramatic changes upon entrapment within the zeolite supercages. Temperature-dependent lifetime measurements indicate that the excited state decays via two thermally accessible upper states.