Raman scattering and FT-IR spectroscopic studies on dithienylethene switches—towards non-destructive optical readout

The non-destructive readout of photochromic memory materials based on the dithienylethene unit both by IR spectroscopy and Raman scattering is explored. A representative series of C5-substituted thienyl hexahydro- and hexafluoro-cyclopentene based photochromes was investigated to explore the effect and potential usefulness of substitution for the development of multicomponent memory materials. The effect of the deposition method on the photochemistry of solid materials containing photochromic dithienylcyclopentene switches was also explored. Photoconversion in the solid state to the closed form was found to be low when starting from the open form, but, in contrast, ring opening to the open state from the closed form was found to be complete. The effect was found to be due to inner filter rather than conformational phenomena. Characteristic vibrational bands for the central dithienyl core are assigned and a comparison made of the vibrational spectroscopic properties of the perhydro- and perfluoro switches. The data enable the determination of the photoconversion achievable in the solid state as well as some assessment of the influence of the deposition method on the photoconversion. The potential of Raman spectroscopy as a method of achieving non-destructive optical readout is demonstrated through the large differences in absolute Raman scattering intensity between the open and closed states, when monitored at wavelengths which do not result in photochemical ring opening.