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Intramolecular electron transfer in donor-acceptor systems. Porphyrins bearing trinitroaryl acceptor group

Bhaskar, Maiya G and Krishnan, V (1985) Intramolecular electron transfer in donor-acceptor systems. Porphyrins bearing trinitroaryl acceptor group. In: Journal of Physical Chemistry, 89 (24). pp. 5225-35.

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Porphyrins bearing picryl group in ortho, meta, and para positions of one of the mesoaryl groups of tetraphenylporphyrin (TPP) were synthesized in the free-base form. The metal [Cu(II) and Zn(II)] derivs. of the free-base picrylporphyrins (PPc) were prepd. The broadened Soret absorption, the decreased optical absorbance values of Q bands, and the reduced singlet emission quantum yields of PPc indicate the existence of intramol. interaction. The extent of this interaction is greater than those obsd. for the intermol. systems and varies with the position at which the picryl moiety is attached to the porphyrin as ortho > meta > para. The energies of the redox states, E(CT) of P+Pc-, calcd. from the electrochem. redox potentials depend on the nature of the metal ion as free-base PPc > CuPPc > ZnPPc. The nature of intramol. interaction between the picryl moiety and porphyrin unit is essentially $\pi-\pi$ (CT). Conclusive evidence for light-induced electron transfer in ZnPPc is presented from EPR studies. The decay profiles of the EPR signals vary with the position of the picryl moiety as ortho < para < meta. Computer simulation of structures substantiated by the 1H NMR results point out the restricted conformational freedom of the picryl moiety in ZnPPc. Arguments based on symmetry considerations of HOMO of the excited singlet state PPc and LUMO of picryl group indicate plane-to-plane orientation of the donor and acceptor in the picrylporphyrins.

Item Type: Journal Article
Publication: Journal of Physical Chemistry
Publisher: American Chemical Society
Additional Information: Copyright belongs to American Chemical Society
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 20 Mar 2008
Last Modified: 19 Sep 2010 04:43
URI: http://eprints.iisc.ac.in/id/eprint/13404

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