Distance Dependence of the Low Temperature Electron Transfer Kinetics of(Ferrocenylcarboxy)-Terminated Alkanethiol Monolayers

摘要

Results are presented for rate constants (k deg) and reorganizational energybarriers Lambda for interfacial electron transfer at ultralow-temperatures (120-150 K) across mixed CpFeCpCO2(CH2)(n)SH/CH3 (CH2)(n-1)SH monolayers (n= 8,12, 16). The monolayers are kinetically disperse, i.e., the ferrocene sites exhibit a range of rate constants. Average values of k deg were measured by cyclic voltammetry with application of Marcus theory corrected for the density of electronic states in the gold electrode. The k deg and pre-exponential values exhibit exponential dependencies on alkane chain length characterized by exponential coefficients of 1.06 and 1. 44/CH2, respectively. The former value agrees with aqueous phase results by others for analogous but more highly ordered monolayers near ambient temperatures; the latter result corresponds to an electronic coupling coefficient of Beta of 1.1 A-1. The activation analysis-derived reorganizational barrier energies decrease somewhat with increasing chain length, contrary to theoretical expectations. jg.