TRIPLET STATE PROPERTIES OF C60PMMA CO-POLYMERS IN ORGANIC SOLUTION AND PMMA FILM

Two star-like C60-polymethylmethacrylate (C60PMMA) copolymers, which are soluble in a wide range of organic solvents, have been synthesized by free-radical polymerization. The polymers can be described by the formula 1%C60PMMA and 10%C60PMMA. They consist of a C60 core with a maximum of 6 polymethylmethacrylate (PMMA) chains. The difference between these derivatives is the weight distribution of C60. Nanosecond pulse radiolysis and laser flash photolysis studies, UV/VIS spectroscopic and fluorescence measurements have been performed to investigate the photophysical properties of 1%C60PMMA and 10%C60PMMA. The absorption spectra of the C60PMMA co-polymers exhibit a band at 210 to 220nm for PMMA and at 330nm for C60 independent of the solvent polarity showing that they have a small dipole moment in the electronic ground state. The triplet-triplet (T-T) absorption spectra of 10%C60PMMA in toluene and chloroform peak at the same wavelength and are broader than those of C60, indicating that they are addition spectra of 10%C60PMMA and neat C60. Physical addition of PMMA increases the solubility of C60 in chloroform, but does not change the T-T absorption spectrum, unless PMMA is chemically bound to C60. Gaussian band analysis of the T-T absorption spectra of 10%C60PMMA results in an additional band for pure 10%C60PMMA at (626.8±15.7)nm in toluene and (652.4±1.9)nm in chloroform. The triplet state lifetime of 10%C60PMMA is smaller than that of C60 at 79μs. The quantum yields of singlet oxygen production (ΦΔ) decrease with the C60 content in the co-polymer. The values for 1%C60PMMA and 10%C60PMMA in polar chloroform are 4% and 26% respectively. The intersystem crossing from S1 to T1 as well as the triplet state lifetime decrease with increasing number and length of PMMA chains connected to C60. 1%C60PMMA also shows no T-T absorption suggesting a relative high photochemical stability for 1%C60PMMA.