The anisotropic thermal expansion properties of an organic semiconducting single crystal constituted by
4-hydroxycyanobenzene (4HCB) have been probed by XRD in the range 120–300 K. The anisotropic
thermal expansion coefficients for the three crystallographic axes and for the crystal volume have been
determined. A careful analysis of the crystal structure revealed that the two different H-bonds stemming
from the two independent, differently oriented 4HCB molecules composing the unit cell have different
rearrangement patterns upon temperature variations, in terms of both bond length and bond angle.
Linearly Polarized Mid InfraRed (LP-MIR) measurements carried out in the same temperature range,
focused on the O–H bond spectral region, confirm this finding. The same LP-MIR measurements, on
the basis of a semi-empirical relation and of geometrical considerations and assumptions, allowed
calculation of the –CN
H–O– hydrogen bond length along the
a
and
b
axes of the crystal. In turn, the
so-calculated –CN
H–O– bond lengths were used to derive the thermal expansion coefficients along
the corresponding crystal axes, as well as the volumetric one, using just the LP-MIR data. Reasonable to
good agreement with the same values obtained from XRD m
easurements was obtained. This proof-of-principle
opens interesting perspectives about the possible development of a rapid, low cost and industry-friendly
assessment of the thermal expansion properties of organic semiconducting single crystals (OSSCs)
involving hydrogen bonds.
