Ultraviolet absorption and emission spectra of propylbenzene in an argon matrix are presented. The spectra are found to consist of several band series that are assigned to different trapping sites of the anti and gauche conformers of the molecule. Comparison with gas phase spectra and ab initio calculations allows the assignment of the vibronic bands of the emission spectrum. Some re-assignments of the observed vibronic bands are proposed. The relatively small number of trapping sites found for this asymmetric molecule is compatible with molecular dynamic simulations that are found to produce a small number of preferred sites.