Comparative raman study of photo-oligomer stability in the donor-acceptor fullerene complex $\{\operatorname{Pt}(\operatorname{dbdtc})_2\}\cdot \mathrm{C}_{60}$ and pristine $\mathrm{C}_{60}$

The photopolymerization process and the stability of the $\mathrm{C}_{60}$ photo-oligomers at elevated temperature in the molecular donor-acceptor fullerene complex $\{\operatorname{Pt}(\operatorname{dbdtc})_2\}\cdot \mathrm{C}_{60}$ ($\mathrm{C}_{60}$ complex with platinum dibenzyldithiocarbamate) and pristine fullerite $\mathrm{C}_{60}$ are studied by Raman spectroscopy. Fast polymerization, manifested by the appearance of additional peaks in the frequency region of the $A_g(2)$ pentagon-pinch (PP) mode of the $\mathrm{C}_{60}$ molecule, was observed upon sample illumination at $514.5$ and $532$ nm, even at low laser power density as well as at $785$ nm at higher power density. The frequencies of the new peaks are in accordance with the empirical dependence of the PP-mode frequency on the number of the $sp^3$-like coordinated carbon atoms per molecular cage. The temperature dependence of the polymer content under constant laser power density reveals the decomposition of the photo-oligomers to monomers at $\sim350$ K in the fullerene complex $\{\operatorname{Pt}(\operatorname{dbdtc})_2\}\cdot \mathrm{C}_{60}$ and at $\sim410$ K in the case of the pristine $\mathrm{C}_{60}$. These values are considerably smaller than the decomposition temperature of $525$ – $565$ K for the crystalline polymers of $\mathrm{C}_{60}$.