Organic semiconducting single crystals (OSSCs) are the subject of intense research due to their intriguing anisotropic, structural and electronic properties [1,2]. OSSCs thermal expansion properties impact the characteristic charge carrier generation/transport phenomena [3]. In general, thermal expansion properties are studied through standard X-ray diffraction (XRD) measurements [4]; however, the long measurement times and cumbersome machinery associated with the latter technique hamper a broad exploitation of this technique. Also considering the possible practical applications of these materials (for example, in field-effect transistors driving light-emitting diodes or sensors [5]) it could be of interest to develop faster and more industry-friendly methods. Here we present a study over the use of a simple, yet accurate method for determining the anisotropic thermal expansion properties of OSSCs based on linearly polarized mid-infrared (LP-MIR) spectroscopy. In particular, the LP-MIR properties of solution-grown 4-hydroxycyanobenzene (4HCB) semiconducting single crystals [6] have been probed at different temperature intervals and have been combined with a known semiempirical method to derive their thermal expansion coefficients (which resulted to be anisotropic) along each crystal axes. These values were validated comparing them with XRD-derived ones in the same temperature interval, and a close match was observed between the two sets of values.
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