Morphology-Dependent Photochemical Events in Aryl Ether Dendrimer Porphyrins:  Cooperation of Dendron Subunits for Singlet Energy Transduction

Abstract

A series of dendrimer porphyrins ((L 5 ) n P, n = 1−4), which bear different numbers ( n ) of five-layered dendron subunits (L 5 ) at the meso -positions of a porphyrin, were synthesized. Upon excitation of the dendron subunits in CH 2 Cl 2 at 20 °C, (L 5 ) n P showed an intramolecular singlet energy transfer from the dendron subunits to the porphyrin core, where tetrasubstituted (L 5 ) 4 P with a spherical morphology exhibited a much higher energy transfer quantum yield (Φ ENT = 80.3%) than partially substituted (L 5 ) 1 P−(L 5 ) 3 P (10.1−31.6%). Fluorescence depolarization characteristics of (L 5 ) 4 P indicated that the excitation energy migrates very efficiently over the continuous dendrimeric array of dialkoxybenzyl building units within the lifetime of the excited state. Consequently, the probability of energy transfer to the porphyrin core was enhanced.