| Abstract
| - We have investigated the resonance Raman (RR) spectra of the directly linked porphyrin arrays in order toelucidate the relationship between excitonic interactions and molecular geometry depending on the numberof pigments in the arrays. The RR spectra obtained by photoexcitation at the high-energy exciton Soret bandsin the arrays are mainly composed of Raman modes localized on the constituent porphyrin monomers. Incontrast, the RR spectra of the arrays with photoexcitation at the low-energy exciton split Soret bands revealsome characteristic Raman bands arising from strong excitonic interactions between the adjacent porphyrinsin the arrays. Based on the RR measurements of the isotope labeled analogues and the normal-mode analysisof the dimer, it is suggested that the photoexcitation at the high-energy Soret band produces an electronicallyexcited state largely localized within a monomer unit and that at the low-energy exciton split Soret band theexcited state is in a way delocalized throughout the array. Normal mode calculation revealed that some of theRR bands of Z2 arise from vibrational splitting by dimeric interactions. Phonon-like behaviors were observedfor some Cm−Cm stretching modes of the arrays, which is ascribed to enhanced polarizability induced byphenyl group movement. Collectively, our data from RR spectroscopic measurements as well as the normal-mode analysis provide a picture of the exciton coupling in relation to the molecular structure of the directlylinked linear porphyrin arrays.
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