The IR spectra of 3,4-benzotropone (2) and naphtho[2,3-c]tropone (3) isolated in nitrogen matrices at 13 K were directly observed. These tropones were generated in the matrices by the photoisomerization of 6,7-benzobicyclo[3.2.0]hepta-3,6-dien-2-one (4) and naphtho[2,3-f]bicyclo[3.2.0]hepta-3,6-dien-2-one (5), respectively. The observed IR bands of the photoproducts were in good agreement with the theoretically predicted bands. The intense C=O/C=C bands of 2 were observed at 1607 and 1615 cm(-1), and the corresponding band of 3 was observed at 1605 cm(-1) with shoulder peaks. The fact that the C=O/C=C band of 3 was observed at a slightly lower wavenumber than the corresponding bands of 2 indicates that benzo-annelation enhanced the contribution of the polarized resonance form to 3. The observed IR spectra of 2 in the nitrogen matrix differed significantly from the spectra observed previously in a CFCl3-CF2BrCF2Br-CHCl3 matrix. Self-consistent reaction field calculations on 2 using the Onsager dipolar-sphere model revealed that the observed differences in the spectra reflect structural changes induced in the tropones by the surrounding media.