J aggregate of a water-soluble porphyrin, 5,10,15,20-tetra(4-sulfophenyl)porphyrin (H2TPPS44−), formed in acidified aqueous solutions, exhibits sharp and intense absorption bands at 491 and 707 nm. These characteristic transitions, J bands, are of linear oscillators polarized in the long axis of rodlike aggregate. The molecules in the aggregate stack so as to lift the degeneracy of the porphyrin planar oscillator excited states. Measurements of flow-induced linear dichroism, circular dichroism, magnetic circular dichroism, as well as polarized fluorescence excitation spectra provide evidence not only of linear oscillator character of the intense J band at 491 nm, but also of presence of another diffuse absorption band around at 420 nm polarized in the short axis of the aggregate, which is the counterpart of the 491 nm band of porphyrin Soret origin. Extrinsic circular dichroism is induced upon addition of L-tartaric acid or by mechanical swirling flow in the period of aggregate growth. Resonance Raman spectrum of the aggregate is rather similar to that of the monomeric diacid except the polarization. The observed shifts of Raman peaks to lower frequency are ascribed to a deformation of porphyrin moiety and/or hydrophobic interaction between component molecules in the aggregate. The sharp and intense J bands polarized in the long axis of aggregate cannot be well described without taking into account the participation of interporphyrin charge resonance excited states, whereas the broadbands polarized in the short axis are exclusively ascribed to exciton resonance excited states. The porphyrin J band is characterized as sustaining an exchange narrowing by fast migration of excitation over the whole system of chromophores in a linear array of the porphyrin planar oscillators in slipped face-to-face stacking.

Luminescence yields and decay lifetimes were measured on some metalloporphyrins including the complexes of the IIIb metal group. The S2 emission was observed for AlClTPP (TPP: tetraphenylporphin), GaClTPP, and InClTPP as well as some other TPP metal complexes, ZnP (P:porphin) and H4P2+ (diacid), while it was not detected for H2TPP, H2OEP (OEP: octaethylporphin), AlClOEP as well as other OEP metal complexes. The rate of S2→S1 internal conversion is dependent upon the peripheral substituents rather than the central metal ion and is enhanced in the porphyrins which do not emit the S2 fluorescence. On the other hand, the intersystem crossing plays a more important part in the relaxation process of the S1 state. With increase in the atomic number of the central metal ion as well as its axial ligand, the yield and decay lifetime of the S1 emission are reduced. In the relaxation of the T1 state, the radiative decay is also accelerated for the central metal ion with higher atomic number.

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The ground state and the lowest excited states of lutetium phthalocyanine dimer radical, [Lu(Pc)2] (Pc: phthalocyanine), and those of related compounds, [Lu(Nc)2] and [Lu(Nc)(Pc)] (Nc: 2,3-naphthalocyanine), are studied by configuration interaction calculations on localized orbital basis set. The orbitals, which are localized on either of two ligands, are obtained by a unitary transformation of semiempirical SCMOs of the dimer. The lowest three bands (7 X 10\ 10 X 103, and 15 X 103 cm-1 for [Lu(Pc)2]; 6 X 103, 8 X 103, and 13 X 103 cm"1 for [Lu(Nc)2]) are assigned to the excited states IB, (|G*)), 2E, (|D->) and 3Ei (|S->), respectively.The ground state of the C* heterodimer, [Lu(Nc)(Pc)], has a population of a hole more in the Nc ring than in the Pc ring. The population shifts toward Pc in the 2A2 excited state.

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