| Abstract
| - We have developed a new route to silicon-centeredphthalocyanines and phthalocyanine-like compoundsthat is robust and flexible, and of considerable potential usefulness.This route entails insertion of silicon into themetal-free macrocycle. It has been developed in the course ofpreparing four new and two known metal-free, sixnew dihydroxysilicon, and six new bis-trihexylsiloxysilicon octabutoxy-and octabutoxybenzophthalocyanines. Oneof the siloxysilicon compounds, that with the ligand5,9,12,16,19,23,28,32-octabutoxy-33H,35H-dibenzo[b,g]dinaphtho[2,3-l:2‘,3‘-q]porphyrazine, has a Q-bandat a wavelength of 804 nm and an extinction coefficient of 1.9 ×105 M-1cm-1. Its wavelength thus matches the wavelength ofthe output of the most common GaAlAs diode laser. Thecompound and its analog in which the benzo rings are transto each other instead of cis have no tendency toaggregatein benzene up to a concentration of 150 μM. The triplet state ofthe cis isomer has an absorption maximum at 640nm and a lifetime in deaerated benzene solution of 105 μs, while thetriplet state of the trans isomer has a maximumat 660 nm and a lifetime of 72 μs. Both isomers have a tripletquantum yield, Qt, of ca. 0.20 and asinglet oxygenquantum yield, QΔ, of ca. 0.20,photochemical properties that are consistent with potentially efficientphotosensitizationaction in photodynamic therapy of tumors. For both sensitizers,energy transfer from the sensitizer triplet to groundstate of dioxygen is reversible at appropriate concentrations. Forthe cis isomer, the equilibrium constant fortheenergy transfer process, Ke, is 0.012 ± 0.001,and the triplet state energy calculated from this,ET, is 21.29 kcal/mol(ET derived from phosphorescence measurements is21.26 kcal/mol). For the trans isomer,Ke is 3.68 × 10-3andET is 19.27 kcal/mol.
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