Exploring a solid polymorphism and phase transitions in 4-cyano-4′-pentylbiphenyl (5CB) and rGO-doped 5CB using temperature dependent Raman spectroscopy

Abstract

Raman spectroscopy is used to examine the temperature-dependent phase transition behaviour of the liquid crystalline system 4-cyano-4′-pentylbiphenyl (5CB) and its nanocomposite with reduced graphene oxide (5CB@rGO) over the temperature range of −160 °C to 90 °C. First time, such a broad temperature range study of 5CB and 5CB@rGO has been reported. The structural and intermolecular interaction characteristics of the liquid crystal 5CB and its behaviour in the presence of reduced graphene oxide (rGO) are examined in depth by the temperature-induced Raman spectra and DFT calculations. To assess the phase transitions in 5CB and 5CB@rGO, the significant bands associated with the polar C[tbnd]N group and phenyl rings were thoroughly examined. A new crystal-crystal (solid polymorphism) phase transition is investigated first time, occurring between −120 °C and −100 °C. Another significant new crystal-crystal phase transition in 5CB and 5CB@rGO is also exposed, taking place between −20 °C and −10 °C. Differential scanning calorimeter (DSC) measurements confirm this new phase transition in 5CB and temperature sensitivity fairly matches Raman analysis. To evaluate the structural as well as change in intermolecular interactions in each phase, the detailed DFT study is performed on the 5CB molecule to establish the spectra-structure relation. The detailed spectra-structure correlation is discussed in this study. The spectra-structure correlation and change in spectral parameters are used to investigate the structure and intermolecular interaction of each phase. © 2025 Elsevier B.V.