Electronic properties of charged fullerenes characterized by EPR and Vis-NIR spectroscopy

Abstract

EPR and Vis-NIR absorption spectra have both been measured for clarification of contradictory statements about the para-and diamagnetic states of fullerenes. Thereby identification of one sharp EPR signal in solution at room temperature to Cia (g = 2.000±4.000l; l1B = O.07±0.01 mT) could be made upon using different fullerene sources (TechnoCarbo, Hoechst) and methods of anion generation (chemically, electrochemically, and photochemically). This fact is also supported by the similar observation for a monosubstituted derivative (g = 1.9999; l1B = 0.10 mT), in which a small broadening of this sharp signal is found originating from additional 'H hyperfine interactions.Furthermore the g-values of the radical anions of C 60 increase with charge (g(C 60 ) < g(Clo~) < < g(Clo~) < g(Cln), indicating largest contributions from spin-orbit coupling for the monoanion. No diamagnetic states for the dianions of [60]-and [70]-fullerenes could be found so far but biradical species with largest zero field splittings D = 2.7 mT (Cl o )and D = 3.1 mT (Cio~)' respectively. The cation formation of C 60 (g = 2.0023-2.0029; l1B = 0.15-0.20 mT) with antimony pentachloride was controlled by mass spectrometry. Stable cations were found only in methylenechloride. In other solvents like toluene addition reactions seem to occur.

Electron Transfer Studies on Self-Assembled Monolayers of Helical Ferrocenoyl-Oligoproline-Cystamine Bound to Gold

“…In general, the b value for the helical polyproline II structure determined electrochemically by us and obtained from photophysical or pulse radiolysis experiments (see below) are significantly lower than the average value of b estimated for proteins (0.9 ± 1.2 ä À1 ). Our values are lower than those reported by Schanze and Sauer [11] and Isied et al [12] from photoinduced electron transfer studies on various labeled oligoprolines in solution. Based on results of studies on H-Tyr(Pro) n -TrpOH and H-Trp(Pro) n -TyrOH, Faraggi and Klapper [13] proposed a through-bond mechanism to explain the low b value of 0.2 ± 0.4 ä À1 in these systems.…”

Development and application of a new electrochemical cell allowing EPR/ENDOR and NIR measurements

“…2, curves a) together with structures at a lower wavelength caused by vibronic interaetions of higher energy (sometimes found as IR resonances). The spectra are in good agreement with earlier C60-measurements [17][18][19][20][21][22][23][24], where additional peaks at 1144 nm and at 1186 nm stem from the absorption of the conducting salt. The extinction coefficient for the peak at 1075 nm of 18000 lmol-lcm -1 lies in the range of values reported earlier [17,20,22,25,26], with the assumption of complete generation of the monoanion.…”

“…Atso the peaks at 840 and 947 nm and the value of e of 15000 lmol-~cm -1 for the peak at 947 nm in the C~0--spectrum of Fig. 2 (curves b) are in good agreement with the literature [22,24,26]. The EPR spectra belonging to the Vis/NIR spectra show two lines at gl = 2.0010 ___ 0.0001 and g2 = 2.0007 + 0.0001 with a linewidth of AB = 0.05 mT for the signal centered at g2 = 2.0007 ___ 0.0001.…”

Discrete Fulleride Anions and Fullerenium Cations

“…104 They have also been used successfully in solution, typically in an ether (e.g., tetrahydrofuran, dimethoxyethane) [105][106][107][108][109] or liquid ammonia. 110,111 C 60 n-fullerides up to n ) 5 have been produced in this manner.…”

“…367 Studies on fullerene derivatives of the type R 2 C 60 -are more appropriate models for the sharp signal in C 60 -. Signals ascribable to such species have been reported to have g values close to 2.000 and line widths of 1-2 G. 108,132,230,232,[368][369][370] In temperaturedependent studies on the well characterized anion of N-methyl [60]fulleropyrollidine, the g value was 2.0006 and the line width was 3 G at room temperature. It decreased to about 1 G at liquid helium temperatures with the onset of noticeable anisotropy.…”