Influence of hydrogen bonding on excitonic coupling and hierarchal structure of a light-harvesting porphyrin aggregate

Abstract

Helical porphyrin nanotubes of tetrakis(4-sulfonatophenyl)porphyrin (TSPP) were examined in DCl/D(2)O solution using resonance Raman and resonance light scattering spectroscopy to probe the influence of hydrogen bonding on the excitonic states. Atomic force microscopy reveals similar morphology for aggregates deposited from DCl/D(2)O and from HCl/H(2)O solution. Deuteration results in subtle changes to the aggregate absorption spectrum but large changes in the relative intensities of Raman modes in the J-band excited resonance Raman spectra, revealing relatively more reorganization along lower-frequency vibrational modes in the protiated aggregate. Depolarization ratio dispersion and changes in the relative Raman intensities for excitation wavelengths spanning the J-band demonstrate interference from overlapping excitonic transitions. Distinctly different Raman excitation profiles for the protiated and deuterated aggregates reveal that isotopic substitution influences the excitonic structure of the J-band. The deuterated aggregate exhibits a nearly two-fold increase in intensity of resonance light scattering as a result of an increase in the coherence number, attributed to decreased exciton-phonon scattering. We propose that strongly coupled cyclic N-mers, roughly independent of isotopic substitution, largely decide the optical absorption spectrum, while water-mediated hydrogen bonding influences the further coherent coupling among them when they are assembled into nanotubes. The results show that, similar to natural light-harvesting complexes such as chlorosomes, hydrogen bonding can have a critical influence on exciton dynamics.

WITHDRAWN: Hydrogen-bonding versus π–π stacking in the design of organic semiconductors: From dyes to oligomers

“…dye solutions, which reveal inter-plane distances of 3.6 Å, the shortest possible distance between the aromatic moieties in the direction perpendicular to their planes.Collings et al[35] demonstrated liquid-crystalline nature of the J-aggregates of benzopurpurin 4B(Fig. 4)highlighting the fact that a considerable fraction of the water is incorporated into the mesophase.Very recently, McHale and Rich[36] showed that water-mediated hydrogen bonds strongly affect the exciton coupling in the J-aggregates of dyes. Aggregation of tetrakis(4-sulfonatophenyl)porphyrin (TSPP)(Fig.…”

Resonance Raman and vibrational mode analysis used to predict ligand geometry for docking simulations of a water soluble porphyrin and tubulin

“…Fortunately, the correlation of Raman peaks of porphyrins with their vibrational modes has been established previously. (Zhang, 2003, Saini, 2006, Bour, 2000) (Aydin, 2014, Rich, 2012 The DFT-calculated frequencies of vibrational modes tend to be overestimated when using the harmonic approximation. (Mroginski, 2006) In order to correct for this effect, the DFT-computed frequencies are scaled according to a scaling quantum mechanical factors (Kozlowski, 1999) in which the frequency is multiplied by a factor depending on the atomic motions involved in the vibrational mode.…”

Supramolecular Principles of Self-Assembly of Pophyrin Nanotubes. 1. Models of SWPNTs Based on 5,10,15,20-Tetrakis(4’-sulfophenyl)porphine Zwitter-Ion

“…Rich and McHale [29] suggested a model of chiral SWPNT with its surface made of 16-dimensional circular ladder-type aggregates, [18] bound together by hydrogen bonds (Figure 12).…”