title: Robust inclusion complexes of crown ether fused tetrathiafulvalenes with Li⁺@C₆₀ to afford efficient photodriven charge separation.
abstract: Inclusion complexes of benzo- and dithiabenzo-crown ether functionalized monopyrrolotetrathiafulvalene (MPTTF) molecules were formed with Li(+)@C60(1⋅Li(+)@C60 and 2⋅Li(+)@C60). The strong complexation has been quantified by high binding constants that exceed 10(6) M(-1) obtained by UV/Vis titrations in benzonitrile (PhCN) at room temperature. On the basis of DFT studies at the B3LYP/6-311G(d,p) level, the orbital interactions between the crown ether moieties and the π surface of the fullerene together with the endohedral Li(+) have a crucial role in robust complex formation. Interestingly, complexation of Li(+)@C60 with crown ethers accelerates the intersystem crossing upon photoexcitation of the complex, thereby yielding (3)(Li(+)@C60)*, when no charge separation by means of (1)Li(+)@C60* occurs. Photoinduced charge separation by means of (3)Li(+)@C60* with lifetimes of 135 and 120 μs for 1⋅Li(+)@C60 and 2⋅Li(+)@C60, respectively, and quantum yields of 0.82 in PhCN have been observed by utilizing time-resolved transient absorption spectroscopy and then confirmed by electron paramagnetic resonance measurements at 4 K. The difference in crown ether structures affects the binding constant and the rates of photoinduced electron-transfer events in the corresponding complex.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, JST, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Supur
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kawashima
authors.forename: Karina R
authors.initials: KR
authors.lastname: Larsen
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Jan O
authors.initials: JO
authors.lastname: Jeppesen
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
mesh_terms: D043844:Crown Ethers / Q000737:chemistry*; D004579:Electron Transport; D037741:Fullerenes / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D008958:Models, Molecular; D055668:Photochemical Processes
chemical_list: D043844:Crown Ethers; D037741:Fullerenes; D006571:Heterocyclic Compounds; D008094:Lithium; C063887:tetrathiafulvalene
keywords: donor-acceptor systems; electron transfer; fullerenes; inclusion; tetrathiafulvalene