Probing the electron-accepting reactivity of isomeric bis(pyrrolidinium) fullerene salts in aqueous solutions
A series of water-soluble isomer bis(pyrrolidinium) salts, with C{sub 60}(C{sub 4}H{sub 10}N{sup +}){sub 2} as cationic moiety (2a--2d), were probed in radical- and light-induced reduction studies and compared to bis(carboxylates) C{sub 60}[C(COO{sup {minus}}){sub 2}]{sub 2} and to {gamma}-CD-encapsulated C{sub 60}. Pulse radiolytic reduction of 2a--2d with hydrated electrons and (CH{sub 3}){sub 2}{sup {sm{underscore}bullet}}COH radicals leads to the formation of the fullerene {pi}-radical anion, exhibiting fingerprint absorption characteristics in the near-IR region. Because of the electron-withdrawing nature of the pyrrolidinium groups the electron-acceptor properties of the investigated bis(pyrrolidinium) salts are markedly improved relative to the bis(carboxylates) (C{sub 60}[C(COO{sup {minus}}){sub 2}]{sub 2}) and also relative to C{sub 60}. For example, the rate constants for the fullerene reduction of 2a--2d with hydrated electrons ((0.88--2.2) x 10{sup 10} M{sup {minus}1} s{sup {minus}1}) and (CH{sub 3}){sub 2}{sm{underscore}bullet}COH radicals ((4.7--7.1) x 10{sup 8} M{sup {minus}1} s{sup {minus}1}) are clearly faster than those noted for C{sub 60}[C(COO{sup {minus}}){sub 2}]{sub 2} (e{sub aq}{sup {minus}}: (0.19--0.34) x 10{sup 10} M{sup {minus}1} s{sup {minus}1}; (CH{sub 3}){sub 2}{sup {sm{underscore}bullet}}COH: (0.9--2.2) x 10{sup 8}M{sup {minus}1} s{sup {minus}1}), and C{sub 60} (e{sub aq}{sup {minus}}: 1.8 x 10{sup 10} M{sup {minus}1} s{sup {minus}1}; (CH{sub 3}){sub 2}{sup {sm{underscore}bullet}}COH: 2.7 x 10{sup 8} M{sup {minus}1} s{sup {minus}1}). Photolysis of 2a--2d gives rise to singlet excited state absorptions that closely resemble earlier observations for the pyrrolidine precursor, e.g., C{sub 60}(C{sub 3}H{sub 7}N){sub 2} (1a--1d) in deoxygenated toluene solutions. The triplet lifetimes of 2a--2d, as measured by nanosecond-resolved photolysis, are typically around 33 {mu}s, similar to the triplet lifetimes of truly monomeric fullerene solutions. Quenching experiments with diszabicyclooctane (DABCO), involving the triplet excited states of 2a--2d, yielded rate constants which vary between 2.5 x 10{sup 6} and 4.7 x 10{sup 6} M{sup {minus}1} s{sup {minus}1} and reveal a slow-down relative to C{sub 60}(7.4 x 10{sup 7} M{sup {minus}1} s{sup {minus}1}).
- Research Organization:
- Univ. of Notre Dame, IN (US)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 20017527
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 7; Other Information: PBD: 24 Feb 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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