Excited-State Processes in First-Generation Phenyl-Cored Thiophene Dendrimers

First generation dendrimers with three oligothiophene arms (meta-arranged, 3G1-nS) and four arms (ortho- and para-arranged, 4G1-nS) connected to a central phenyl core were investigated spectroscopically in solution. In all dendrimers, on an ultrafast time scale (0.6 ns−1) is observed in both dendrimer series, possibly due to increased twisting about the phenyl core that reduces the triplet yields considerably with respect to oligothiophenes. An anomalous shifting of the triplet−triplet absorption spectra characterizes the 4G1-nS dendrimers as unique from the 3G1-nS series in terms of the hindrance of torsional motion and confinement of excited states enforced by the arrangement of dendrons.