Multidimensional Electron Transfer Pathways in a Tetrahedral Tetrakis{4-[N,N-di(4-methoxyphenyl)amino]phenyl}Phosphonium Salt: One-Step vs Two-Step Mechanism

Different electron-transfer pathways have been investigated in a three-dimensional redox system: tetrakis{4-[ N,N -di(4-methoxyphenyl)amino]phenyl}phosphonium tetrafluoroborate 1 + BF 4 - which comprises of four triarylamine redox centers arranged in a pseudo-tetrahedral geometry. Using a UV/Vis/NIR spectroelectrochemical setup we generated the mixed-valence species 1 2+, 1 3+, and 1 4+ and measured the UV/Vis/NIR spectra. These spectra were analyzed and interpreted according to a multi-dimensional Marcus−Hush approach. The analysis revealed that both the photoexcited as well as the thermal ET in 1 3+ are forbidden as a concerted two-electron transfer but allowed as two consecutive one-electron transfer steps.