Substituent effects in a series of 1,7-C60(RF)2 compounds (RF = CF3, C2F5, n-C3F7, i-C3F7, n-C4F9, s-C4F9, n-C8F17): electron affinities, reduction potentials and E(LUMO) values are not always correlated

A series of seven structurally-similar compounds with different pairs of R-F groups were prepared, characterized spectroscopically, and studied by electrochemical methods (cyclic and square-wave voltammetry), low-temperature anion photoelectron spectroscopy, and DFT calculations (five of the compounds are reported here for the first time). This is the first time that a set of seven R-F groups have been compared with respect to their relative effects on E-1/2(0/-), electron affinity (EA), and the DFT-calculated LUMO energy. The compounds, 1,7-C-60(R-F)(2) (R-F = CF3, C2F5, i-C3F7, n-C3F7, s-C4F9, n-C4F9 and n-C8F21), were found to have statistically different electron affinities (EA), at the +/- 10 meV level of uncertainty, but virtually identical first reduction potentials, at the +/- 10 mV level of uncertainty. The lack of a correlation between EA and E-1/2(0/-), and between E(LUMO) and E-1/2(0/-), for such similar compounds is unprecedented and suggests that explanations for differences in figures of merit for materials and/or devices that are based on equating easily measurable E-1/2(0/-) values with EAs or E(LUMO) values should be viewed with caution. The solubilities of the seven compounds in toluene varied by nearly a factor of six, but in an unpredictable way, with the C2F5 and s-C4F9 compounds being the most soluble and the i-C3F7 compound being the least soluble. The effects of the different R-F groups on EAs, E(LUMO) values, and solubilities should help fluorine chemists choose the right R-F group to design new materials with improved morphological, electronic, optical, and/or magnetic properties.