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Abstract
Crystals of the toluene sulfonate polydiacetylene have been prepared in an oxygen-free environment. Upon exposure to O2, micro-crystals of the polymer were found to absorb an amount of gas equivalent to approximately two molecules per unit cell. Analysis of x-ray structural data suggested that the absorbed O2 must reside on the surface or at crystalline defects. Adsorption of 16O2 and 18O2 on the surface of macro-crystals was monitored by the appearance of extra lines in the resonance Raman spectrum. Excitation profiles of the extra lines indicate that the presence of O2 induced additional electronic transitions at 2.4 and 2.6 eV. The lower in energy has been tentatively identified as an electronic excitation on the perturbed backbone while the higher involves charge transfer between the backbone and the adsorbed O2 molecule. Both types of excitation lead to photooxidation of the crystal surface.