Site-selective line-narrowed fluorescence spectra have been obtained for the S-1<->S-0 transitions of phenanthrene and perylene in polyethylene, polystyrene, and poly(methyl methacrylate) films at 1.5 K. The spectral distributions and intensities of the phonon sidebands on each vibronic transition are analyzed to examine the chromophore, matrix, and vibrational level dependence of the coupling of the chromophore's electronic transition to matrix and/or intermolecular vibrations. The frequency distribution of the coupled phonons (spectral density) and the strength of the coupling vary considerably among polymers. Different vibronic transitions of the same chromophore in the same matrix exhibit similar spectral densities but slightly different coupling strengths. The coupling strengths appear to correlate with the extent to which the normal mode changes the molecule's overall dimensions. The more redshifted absorbers within a given chromophore and matrix also exhibit slightly stronger coupling to matrix phonons. Computational simulations of the emission spectra have been performed in order to examine transferability of the spectral densities between different vibronic bands of the same chromophore and between chromophores in the same matrix. Somewhat different spectral densities are required to model vibronic bands of different chromophores in the same polymer.