The influence of polymer matrix on emission spectra of low molecular ketones at 77 K

The emission spectra of five low molecular ketones (benzophenone, 9-anthrone, 9,10-anthraquinone, xanthone and thioxanthone) in polymeric matrices, namely polyethylene (PE), isotactic polypropylene (iPP), atactic polypropylene (aPP), polystyrene (PS) and poly(methyl methacrylate) (PMMA), exhibit the same main features as in non-polar and polar glasses of low molecular solvents at 77 K. The emission spectrum of benzophenone is least dependent on polymer matrix. The best vibrationally resolved spectrum of anthrone and xanthone is attained in non-polar matrices such as PE, iPP and aPP at low concentration. The intensity of the short wavelength vibrational bands decreases whilst that of the long wavelength bands increases with increased concentration of ketone in the range between 0·1 and 3 wt%. Emission spectra of anthrone and xanthone are most sensitive to the polarity of the polymer matrix. No difference is observed in the emission spectra of aryl carbonyl chromophores in the microcrystalline and amorphous polymer matrices. Mono-exponential decay of the emission is observed for benzophenone, 9-anthrone and 9,10-anthraquinone in all matrices under study. The decay of xanthone emission is bi-exponential in all matrices. Thioxanthone exhibits bi-exponential decay in non-polar matrices such as PE and PP and mono-exponential in polar matrices such as PMMA and PS.

The sensitivity of the emission of 9-anthrone and xanthone can be used for evaluating the polarity of the polymer matrix. The concentration effect can substantially influence the spectra of low molecular compounds dispersed in the polymer matrix.