The photopolymerization rate and activation energy of C60 rotations in fullerene and its molecular complexes

Abstract

The temperature dependence of the photopolymerization rate in pristine C60 and fullerene molecular complexes {Pt(dbdtc)2}•C60 and {Pt(nPr2dtc)2}•(C60)2 was studied. The Raman spectra measured in the temperature region 190–323 K exhibit an intensity increase of the dimer-related Ag(2) mode of the C60 molecule and a decrease of the monomer’s one under long laser irradiation. The photopolymer content grows exponentially with the laser exposure time while the growth time constant decreases with the increase of temperature. Since the polymerization via the 2 + 2 cycloaddition reaction necessitates the parallel orientation of double C = C bonds of neighboring C60 molecules, the acceleration of fullerene rotations at elevated temperatures affects the polymerization rate. The photopolymerization rate under fixed conditions of laser power, excitation wavelength and beam focusing exhibits an activation-type dependence on temperature. The activation energy EA, obtained from the Arrhenius dependence of the polymer growth time constant on the temperature, increases from (0.13 ± 0.01) eV and (0.18 ± 0.01) eV for {Pt(nPr2dtc)2}•(C60)2 and {Pt(dbdtc)2}•C60 molecular complexes to (0.24 ± 0.04) eV for pristine C60.