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Issue 2, 2011
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Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies

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Abstract

The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D–A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g.fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D–A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >1012 s−1. Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D–A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications.

Graphical abstract: Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies

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Publication details

The article was received on 07 Jul 2010, accepted on 24 Sep 2010 and first published on 29 Oct 2010


Article type: Perspective
DOI: 10.1039/C0CP01106A
Citation: Phys. Chem. Chem. Phys., 2011,13, 397-412

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    Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies

    H. Lemmetyinen, N. V. Tkachenko, A. Efimov and M. Niemi, Phys. Chem. Chem. Phys., 2011, 13, 397
    DOI: 10.1039/C0CP01106A

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