Cyanobuta-1,3-dienes as Novel Electron Acceptors for Photoactive Multicomponent Systems

• Published in: Chemistry : a European journal Vol. 20; no. 1; pp. 202 - 216
• Main Authors: Tancini, Francesca, Monti, Filippo, Howes, Kara, Belbakra, Abdelhalim, Listorti, Andrea, Schweizer, W. Bernd, Reutenauer, Philippe, Alonso-Gómez, José-Lorenzo, Chiorboli, Claudio, Urner, Lorenz M., Gisselbrecht, Jean-Paul, Boudon, Corinne, Armaroli, Nicola, Diederich, François
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 03.01.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: 3-dienes; Benzonitrile; Charge; Chemistry; Chemistry, Multidisciplinary; cyanobuta-1; cyanobuta‐1,3‐dienes; electron acceptors; Electron transfer; Excitation; Luminescence; photoinduced electron transfer; photoinduced energy transfer; Physical Sciences; Porphyrins; Science & Technology; singlet oxygen luminescence; Spacers; Toluene; SOLAR-CELLS; QUANTUM YIELDS; COMPLEXES; singlet oxygen luminescence; PORPHYRIN; porphyrins; CYCLOADDITION; cyanobuta-1,3-dienes; CHEMISTRY; photoinduced electron transfer; ENERGY-TRANSFER; photoinduced energy transfer; CHARGE-TRANSFER INTERACTIONS; BASIS-SET; EFFICIENCY; electron acceptors
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201303284

The synthesis, electrochemical, and photophysical properties of five multicomponent systems featuring a ZnII 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 (ΔGCR=−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. Catch the electron: Strongly electron‐accepting multicyanobuta‐1,3‐dienes provide a new class of electron acceptors for incorporation into photoactive multicomponent systems. Photophysical and electrochemical investigations revealed photoinduced intramolecular electron transfer (PET) from a ZnII porphyrin to 1,1,4,4‐tetracyanobuta‐1,3‐diene acceptor sites appended by an insulating spacer, with a long‐lived charge‐separated excited state of 2.3 μs in benzonitrile.