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.