title: Cyanobuta-1,3-dienes as novel electron acceptors for photoactive multicomponent systems.
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.
authors: Laboratorium für Organische Chemie, ETH Zürich, Hönggerberg, HCI, 8093 Zürich (Switzerland), Fax: (+41) 44-632-1109.
authors: Francesca
authors: F
authors: Tancini
authors: Filippo
authors: F
authors: Monti
authors: Kara
authors: K
authors: Howes
authors: Abdelhalim
authors: A
authors: Belbakra
authors: Andrea
authors: A
authors: Listorti
authors: W Bernd
authors: WB
authors: Schweizer
authors: Philippe
authors: P
authors: Reutenauer
authors: José-Lorenzo
authors: JL
authors: Alonso-Gómez
authors: Claudio
authors: C
authors: Chiorboli
authors: Lorenz M
authors: LM
authors: Urner
authors: Jean-Paul
authors: JP
authors: Gisselbrecht
authors: Corinne
authors: C
authors: Boudon
authors: Nicola
authors: N
authors: Armaroli
authors: François
authors: F
authors: Diederich
keywords: cyanobuta-1,3-dienes; electron acceptors; photoinduced electron transfer; photoinduced energy transfer; porphyrins; singlet oxygen luminescence