On the relation of energy and electron transfer in multidimensional chromophores based on polychlorinated triphenylmethyl radicals and triarylamines†
A star-like compound consisting of a polychlorinated triphenylmethyl radical (PCTM) core linked to three triarylamines (TAA) and a symmetric and an asymmetric hexaarylbenzene (HAB) both substituted with three PCTMs and three TAAs were synthesised. In the star-like compound a strong communication between the redox centres was observed by electron paramagnetic resonance spectroscopy and UV/Vis/NIR absorption measurements, whereas in the HABs only a weak interaction could be detected. The temporal evolution of the excited states was monitored by ultrafast transient absorption measurements. Within the first picosecond stabilisation of the charge transfer state was observed induced by solvent rotation. Anisotropic transient absorption measurements revealed that within the lifetime of the excited state (τ = 1–4 ps) energy transfer does not occur in the HABs whereas in the star-like system ultrafast and possibly coherent energy redistribution is observed. Taken this information together we made the identity between energy transfer and electron transfer in the specific systems apparent.