Various crystalline phases of N-(2-hydroxy-4-methoxybenzylidene)-4′-n-butylaniline (OHMBBA) identified by a simultaneous measurement of DSC-XRD and DSC-Raman spectroscopy

The effect of precooling treatments on phase behaviors of N-(2-hydroxy-4-methoxybenzylidene)-4′-n-butylaniline (OHMBBA) was investigated by differential scanning calorimetry (DSC) measurements. OHMBBA shows polymorphism with several metastable phases. We found that OHMBBA forms various solid phases depending on the cooling conditions, crystalline phases, glassy–liquid–crystal states, or a mixture of both. DSC-X-ray diffraction (XRD) clearly showed that OHMBBA crystallizes into new metastable phase (CII′) when cooled at 10 K min−1 and stabilizes into the most stable phase (CI) during the heating process. We performed the simultaneous measurement of DSC-Raman spectroscopy for OHMBBA and successfully distinguished various crystalline phases and a glassy N phase thermally and/or spectroscopically. The exothermic heat by the irradiation for Raman spectroscopy was characteristics of the phases, which was observed by DSC in the simultaneous measurement. In addition, roughly continuous measurements of Raman spectroscopy detected the phase transitions of OHMBBA complementarily. This work demonstrates that DSC-Raman spectroscopy is very useful to detect the phase transitions and to identify the phases.