MORPHOLOGY-DEPENDENT PHOTOCHEMICAL EVENTS IN ARYL ETHER DENDRIMER PORPHYRINS - COOPERATION OF DENDRON SUBUNITS FOR SINGLET ENERGY TRANSDUCTION

A series of dendrimer porphyrins ((L5)(n)P, n = 1-4), which bear diffe rent numbers (n) of five-layered dendron subunits (L5) at the meso-pos itions of a porphyrin, were synthesized. Upon excitation of the dendro n subunits in CH2Cl2 at 20 degrees C, (L5)(n)P showed an intramolecula r singlet energy transfer from the dendron subunits to the porphyrin c ore, where tetrasubstituted (L5)(4)P with a spherical morphology exhib ited a much higher energy transfer quantum yield (Phi(ENT) = 80.3%) th an partially substituted (L5)(1)P-(L5)(3)P (10.1-31.6%). Fluorescence depolarization characteristics of (L5)(4)P indicated that the excitati on energy migrates very efficiently over the continuous dendrimeric ar ray of dialkoxybenzyl building units within the lifetime of the excite d state. Consequently, the probability of energy transfer to the porph yrin core was enhanced.