A new family of donor-acceptor systems comprising tin(IV) porphyrin and anthracene subunits: Synthesis, spectroscopy and energy transfer studies |
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Authors: | A Ashok kumar L Giribabu and Bhaskar G Maiya |
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Institution: | (1) School of Chemistry, University of Hyderabad, 500 046 Hyderabad, India |
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Abstract: | A new family of covalently linked ‘Sn(IV) porphyrin-anthracene’ diad (1), triad (2) and tetrad (3) donor-acceptor (D-A) systems
have been designed and synthesized in good-to-moderate yields. While diad 1 possesses one anthracene subunit at the peripheral
(meso) position of the tin(IV) porphyrin scaffold, triad 2 possesses twotrans axial anthracene subunits at the tin(IV) centre. On the other hand, tetrad 3 is endowed with both the peripheral and axial
anthracene subunits in its architecture. These D-A systems have been fully characterised by elemental analysis, FAB-MS, UV-Vis,1H and13C NMR and electrochemical methods. UV-Vis,NMR and redox data suggest the absence of intramolecular π-π interaction between
the porphyrin and the anthracene/s in 1–3. Fluorescence from the anthracene subunit in 1 and 3 is found to be quenched in
comparison with the fluorescence of free anthracene in four different solvents. This is not the case with compound 2. Excitation
spectral data provides evidence for an intramolecular excitation energy transfer (EET) from the singlet anthracene to the
porphyrin in 1 and 3. The energy transfer efficiency is in the order: 2 (almost negligible) < 3 (~30%) < 1 (nearly quantitative),
with the peripheral anthracene → porphyrin pathway being largely favoured. This orientation dependence of EET could be analysed
using Forster's dipole dipole mechanism. |
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Keywords: | Tin (IV) porphyrin anthracene spectroscopy energy transfer orientation dependence |
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