Synthesis and Phase Transition Behavior of 2-Amino-4-(halophenyl)-6-methyl-5-(morpholine-4-carbonyl)-4H-pyran-3-carbonitrile Derivatives for Liquid Crystal Applications

This study aimed to synthesize and characterize a series of 2-amino-6-methyl-5-(morpholine-4-carbonyl)-4-(mono- and dihalophenyl)-4H-pyran-3-carbonitrile derivatives 4a–4e through a one-pot multicom­ponent reaction. The primary focus was to investigate their phase transition behavior and assess their potential for liquid crystalline applications, particularly in display and optoelectronic technologies. The synthesized derivatives were characterized using spectroscopic techniques to confirm their molecular structures. Their phase transition behaviors were analyzed using polarized optical microscopy (POM) to identify liquid crystalline properties, including nematic and isotropic phase transition temperatures. The results indicated that compounds 4d and 4e exhibited nematic behavior, transitioning at 171.8 and 185.6°C, respectively, while 4a, 4b, and 4c transitioned directly to the isotropic phase within the temperature range of 185.7–221.6°C, lacking liquid crystalline properties. The presence of mono- or dihalophenyl played a crucial role in promoting nematic behavior, enabling structured molecular arrangements in 4d and 4e. These findings highlight the significance of molecular design in developing liquid crystal materials for advanced applications such as displays and optoelec­tronics, while non-mesomorphic derivatives may be more suited for applications in organic semiconductors or pharmaceuticals. The study successfully identified two halogen-substituted 4H-pyran derivatives with nematic liquid crystalline behavior, emphasizing the importance of halogen substituents in tuning phase transition properties. These insights contribute to a broader understanding of functional material design and pave the way for further exploration of liquid crystal-based applications.