Electronic modulations brought about on ionic metalloporphyrins by various polymeric environments were investigated in detail with spectral analysis. The porphyrins employed were metalloderivatives of anionic p-sulfonated tetraphenylporphyrins [MTPPS; M = Cu(II), Zn(II), Ag(II), and Cd(II)]. The polymer system chosen involved poly(4-vinylpyridine) (PVP), crosslinked and linear polystyrenes partially chloromethylated and quaternized (PS and PS′), and polyethylene glycol (PEG). These were expected to interact with MTPPS through a coordinate bond on its central metal atom (PVP), through Coulombic attraction (PS and PS′), or through ion-dipolar interaction (PEG). Significant changes in the electronic spectra (redshifts in both B and Q bands) were seen in polymer-incorporated MTPPS in comparison with free MTPPS. For a given metalloporphyrin, the order of the spectral shifts was always MTPPSZn>Ag>Cu. This is explained in terms of the molecular distortions and associated changes in the metalloporphyrin orbital overlap and the charge delocalization from the peripheral substituents or coordinating ligand functions to the porphyrin π framework.
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M.V. Vinodu and Prof. M. Padmanabhan, “Electronic effect of polymeric environments on metalloporphyrins”, Journal of Polymer Science, Part A: Polymer Chemistry, vol. 39, pp. 326-334, 2001.