Synthesis and optical properties of perylene diimide derivatives with triphenylene-based dendrons linked at the bay positions through a conjugated ethynyl linkage

A number of groups including trimethylsilyl, phenyl, triphenylene, and triphenylene-based dendron have been linked to the bay positions of a perylene diimide (PDI) core through an ethynyl bridge. The photophysical properties of the resulting bay-substituted PDI derivatives have been carefully studied in different solvents and as thin films. Without any capping group, the two ethynyl bay-substituted PDI derivates PAT and PRT both aggregate strongly even in dilute solutions but in different perylene-perylene π-π stacking modes; PRT aggregates through slipped (or longitudinal) stacking while PAT self-assembles by rotational (or cross) stacking. With capping groups, the perylene core stacking is completely blocked for PATS in both solution and solid film. For PRTS, the slipped stacking is observed only for its film sample, while for PTB, association only occurs after excitation (excimer formation). When triphenylene or triphenylene-based G1 dendron is attached to the acetylene bridge, the resulting donor-acceptor systems (PTG0 and PTG1) exhibit strong electronic coupling between the dendritic donors and the PDI acceptor, leading to significantly red-shifted absorption bands. The conjugated linkage also facilitates photoinduced electron transfer from the triphenylene or triphenylene dendron to the PDI core, effectively quenching fluorescence emissions of both the donor and the acceptor. The significantly red-shifted absorption bands and the efficient photoinduced electron transfer observed on PTG0 and PTG1 indicate that these new PDI derivatives may find applications in solar cells.