Long-lived charge separation in novel axial donor-porphyrin-acceptor triads based on tetrathiafulvalene, aluminum(III) porphyrin and naphthalenediimide.

Prashanth K Poddutoori, Niloofar Zarrabi, Andrey G Moiseev, Roger Gumbau-Brisa, Serguei Vassiliev, Art van der Est

Department Chemistry, Brock University, 500 Glenridge Ave., St.Catharines, ON, L2S 3A1, Canada. ppodduto@brocku.ca

Chemistry (Weinheim an der Bergstrasse, Germany) 2013 Feb 25

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Two self-assembled supramolecular donor-acceptor triads consisting of Al(III) porphyrin (AlPor) with axially bound naphthalenediimide (NDI) as an acceptor and tetrathiafulvalene (TTF) as a secondary donor are reported. In the triads, the NDI and TTF units are attached to Al(III) on opposite faces of the porphyrin, through covalent and coordination bonds, respectively. Fluorescence studies show that the lowest excited singlet state of the porphyrin is quenched through electron transfer to NDI and hole transfer to TTF. In dichloromethane hole transfer to TTF dominates, whereas in benzonitrile (BN) electron transfer to NDI is the main quenching pathway. In the nematic phase of the liquid crystalline solvent 4-(n-pentyl)-4'-cyanobiphenyl (5CB), a spin-polarized transient EPR spectrum that is readily assigned to the weakly coupled radical pair TTF(.+)NDI(.-) is obtained. The initial polarization pattern indicates that the charge separation occurs through the singlet channel and that singlet-triplet mixing occurs in the primary radical pair. At later time the polarization pattern inverts as a result of depopulation of the states with singlet character by recombination to the ground state. The singlet lifetime of TTF(.+)NDI(.-) is estimated to be 200-300 ns, whereas the triplet lifetime in the approximately 350 mT magnetic field of the X-band EPR spectrometer is about 10 μs. In contrast, in dichloromethane and BN the lifetime of the charge separation is <10 ns. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Citation

Prashanth K Poddutoori, Niloofar Zarrabi, Andrey G Moiseev, Roger Gumbau-Brisa, Serguei Vassiliev, Art van der Est. Long-lived charge separation in novel axial donor-porphyrin-acceptor triads based on tetrathiafulvalene, aluminum(III) porphyrin and naphthalenediimide. Chemistry (Weinheim an der Bergstrasse, Germany). 2013 Feb 25;19(9):3148-61