Chemistry. 2014 Jan 03;20(1):202-16. doi: 10.1002/chem.201303284. Epub 2013 Dec 12.

Cyanobuta-1,3-dienes as novel electron acceptors for photoactive multicomponent systems.

Chemistry (Weinheim an der Bergstrasse, Germany)

Francesca Tancini, Filippo Monti, Kara Howes, Abdelhalim Belbakra, Andrea Listorti, W Bernd Schweizer, Philippe Reutenauer, José-Lorenzo Alonso-Gómez, Claudio Chiorboli, Lorenz M Urner, Jean-Paul Gisselbrecht, Corinne Boudon, Nicola Armaroli, François Diederich

PMID: 24339058 DOI: 10.1002/chem.201303284

Abstract

The synthesis, electrochemical, and photophysical properties of five multicomponent systems featuring a Zn(II) porphyrin (ZnP) linked to one or two anilino donor-substituted pentacyano- (PCBD) or tetracyanobuta-1,3-dienes (TCBD), with and without an interchromophoric bridging spacer (S), are reported: ZnP-S-PCBD (1), ZnP-S-TCBD (2), ZnP-TCBD (3), ZnP-(S-PCBD)2 (4), and ZnP-(S-TCBD)2 (5). By means of steady-state and time-resolved absorption and luminescence spectroscopy (RT and 77 K), photoinduced intramolecular energy and electron transfer processes are evidenced, upon excitation of the porphyrin unit. In systems equipped with the strongest acceptor PCBD and the spacer (1, 4), no evidence of electron transfer is found in toluene, suggesting ZnP→PCBD energy transfer, followed by ultrafast (<10 ps) intrinsic deactivation of the PCBD moiety. In the analogous systems with the weaker acceptor TCBD (2, 5), photoinduced electron transfer occurs in benzonitrile, generating a charge-separated (CS) state lasting 2.3 μs. Such a long lifetime, in light of the high Gibbs free energy for charge recombination (ΔG(CR)=-1.39 eV), suggests a back-electron transfer process occurring in the so-called Marcus inverted region. Notably, in system 3 lacking the interchromophoric spacer, photoinduced charge separation followed by charge recombination occur within 20 ps. This is a consequence of the close vicinity of the donor-acceptor partners and of a virtually activationless electron transfer process. These results indicate that the strongly electron-accepting cyanobuta-1,3-dienes might become promising alternatives to quinone-, perylenediimide-, and fullerene-derived acceptors in multicomponent modules featuring photoinduced electron transfer.

Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Keywords: cyanobuta-1,3-dienes; electron acceptors; photoinduced electron transfer; photoinduced energy transfer; porphyrins; singlet oxygen luminescence

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• Journal Article