posted on 2024-04-23, 11:33authored byYuefeng Bai, Chaofan Lan, Wen-Hao Yu, Ruo-Xin Li, Wenqian Li, Kan Zhang, Ke-Qing Zhao, Ping Hu, Yen Wei, Kangmin Niu
Two
palladium complexes (Pd[DiTP-triazole]2Cl2 and Pd[TrTP-triazole]2Cl2) bearing a 1,2,3-triazole segment as ligands
were synthesized. The 1,2,3-triazole moiety in Pd[DiTP-triazole]2Cl2 was synthesized by the Cu(I)-catalyzed azide–alkyne cycloaddition
reaction. Meanwhile, the 1,2,3-triazole in Pd[TrTP-triazole]2Cl2 were synthesized through the Click reaction involving an internal
alkyne and an organic azide. These two complexes feature soft spacers
of comparable length between the triphenylene cores and the 1,2,3-triazole
units, which are designed to enhance the molecular symmetry and improve
the liquid crystalline properties. The structures of both complexes
were fully characterized, with a specific focus on their confirmation
through single-crystal X-ray diffraction (XRD) analysis of two model
molecules, Pd[DiB-triazole]2Cl2 and Pd[TrB-triazole]2Cl2. Additional techniques, such as differential scanning calorimetry
(DSC), polarizing optical microscopy (POM), and powder XRD, were used
to confirm the room temperature discotic liquid crystal (DLC) properties
of all palladium complexes. It was found that both complexes Pd[DiTP-triazole]2Cl2 and Pd[TrTP-triazole]2Cl2 exhibit hexagonal
columnar mesophases at room temperature. Significantly, the temperature
ranges of these mesophases were substantially extended, showing increases
of 70 and 56 °C, respectively, compared to their ligands. Additionally,
upon excitation at 279 nm, all the ligands and complexes emit ultraviolet
to visible blue light as for the critical role of the triphenylene
cores.