Piezomodulation spectroscopy of molecular crystals. II. The pyromellitic dianhydride–anthracene electron donor–acceptor complex

Piezomodulated reflection spectra are presented for the crystalline complex of pyromellitic dianhydride–anthracene. Two differently polarized charge transfer transitions are found and their strain sensitivities are obtained. The role of the charge transfer interaction in determining the magnitude of the piezomodulation is assessed. The piezomodulation spectra are found to have the response expected for an oriented gas. Significant enhancement of structure is also observed and is correlated with structure observed at 20 K.