Probing Charge Separation in Structurally Different C60/exTTF Ensembles

• Published in: Journal of organic chemistry Vol. 68; no. 20; pp. 7711 - 7721
• Main Authors: Díaz, Marta C, Herranz, Ma Angeles, Illescas, Beatriz M, Martín, Nazario, Godbert, Nicolas, Bryce, Martin R, Luo, Chuping, Swartz, Angela, Anderson, Greg, Guldi, Dirk M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 03.10.2003
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Materials science; Physics; Specific materials; Amphoteric; Absorption spectroscopy; 1,3-Dipolar cycloaddition; Radical pair; Charge separation; Electron transfer; Tetrathiafulvalene derivatives; Singlet state; Excited states; Anthracene derivatives; Steady state; Transients; Cyclic voltammetry; Fullerene; Time resolution; Lifetime; Sulfur heterocycle; Photoinduction; Fullerenes; Benzonitrile derivatives; Diels-Alder reaction; Redox system; Ethylenic compound; Electron donor
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo034432e

The scope of the present work is to highlight the effects stemming from different C60/exTTF linkages (exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene)either via an anthracene unit or a dithiole ring. Particular emphasis is placed on photoinduced electron-transfer features. Therefore, we devised a new series of C60-exTTF ensembles, synthesized via 1,3-dipolar cycloaddition and Diels−Alder cycloaddition reactions, in which exTTF units are separated from C60 by two single bonds (3a−c, 4), one vinylene unit (5a), or two vinylene units (5b). The cyclic voltammetry reveals an amphoteric redox behavior with remarkably strong electron-donor ability of the trimethyl-substituted exTTF moiety in 4 and 5a,b. Steady-state and time-resolved photolytic techniques show that the fullerene singlet excited state in (3a−c, 4, and 5a,b) is subject to a rapid electron-transfer quenching. The resulting charge-separated states, that is C60 •--exTTF•+, were identified by transient absorption spectroscopy. We determined radical pair lifetimes of the order of 200 ns in benzonitrile. This suggests (i) that the positive charge of the exTTF•+ is delocalized over the entire donor rather than localized on one of the 1,3-dithiole rings and (ii) that linking exTTF via the anthracene or 1,3-dithiole ring has no appreciable influence. Increasing the donor−acceptor separation via implementing one or two vinylene units as spacers led to improved radical pair lifetimes (5a:  τ = 725 ns; 5b:  τ = 1465 ns).