[Show abstract][Hide abstract] ABSTRACT: We investigated rapid energy transfer (ET) processes in dendrimers having meta-linked branching light harvesting antennas. It was found that, at room temperature (RT), the rapid ET occurs efficiently from the antennas to the core and gives rise to intense core-PL bands under the selective excitation on the antenna. However, the ET efficiency impairs at lower temperatures than ～100 K. For understanding these experimental results, we analyzed molecular vibrations and molecular orbitals of a simple model molecule. From these analyses, it was demonstrated that the torsional vibration of the entire antenna subunit is excited sufficiently at RT and the rapid ET in phDGn dendrimer is realized via the π*-conjugated network mediated by thermal activation of this torsional vibration.
[Show abstract][Hide abstract] ABSTRACT: Energy transfer and shielding effect are studied in wire-type dendrimers (GnPPV: n = 1, 2) having oligophenylene light-harvesting (LH-) antennas. Backbone-polymers in GnPPV give rise to intense photoluminescence (PL) bands under the excitation of the LH-antennas on account of highly efficient energy transfer from the antennas to the backbones. The intensity of backbone-PL uprises faster than the decay of the antenna-PL. This result indicates that rapid energy-transfer from antenna to backbone takes place utilizing the overlap of wavefunctions in their excited states. In solid films of G2PPV having larger LH-antenna, smaller red shifts of the backbone-PL bands than those of G1PPV are observed. This result suggests that the larger LH-antenna in G2PPV substantially wraps its backbone-polymer and shields the inter-backbone interactions in solid films.