Optical, resonance Raman, and resonance light scattering spectroscopy of hierarchal helical nanotube aggregates of tetrakis(4-sulfonatophenyl)porphyrin (TSPP) in DCl/D2O evidence the crucial role of water in the resulting structural and electronic properties of porphyrin self-assemblies. While atomic force microscopy (AFM) images show no structural change in comparison to their protiated counterparts, deuterated aggregates exhibit an increase in the width of the observed J-band, large changes in the relative intensities of resonance Raman modes, and a nearly two-fold enhancement of the resonance light scattering (RLS) J-band. Depolarization ratio dispersion observed in both protiated and deuterated aggregates evidence weak splitting of the J-band into parallel and perpendicular helical excitons. The results presented here support a hierarchal helical model of the porphyrin aggregates wherein phonon modes involving water-mediated hydrogen bonds moderate the coherent coupling of cyclic N-mers and influence the splitting of the J-band into transverse and longitudinal excitons.

Surprising influence of water on exciton-phonon coupling in light-harvesting self-assemblies

243rd National Meeting (2012)

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