Cyclometalated Platinum(II) Complexes of 1,3-Bis(1‑n‑butylpyrazol-3-yl)benzenes: Synthesis, Characterization, Electrochemical, Photophysical, and Gelation Behavior Studies

A new series of cyclometalated platinum­(II) complexes of N^C^N ligands, where N^C^N = 1,3-bis­(1-n-alkylpyrazol-3-yl)­benzene (bpzb), namely, [Pt­(bpzb)­Cl] (1 and 2) and [Pt­(bpzb)­(CC–R)] (310) (R = C6H5, C6H4–OCH3-p, C6H4–NO2-p, C6H4–NH2-p, 4-cholesteryl phenyl carbamate, and cholesteryl methylcarbamate) were synthesized and characterized. Their electrochemical and photophysical properties were investigated. Two of the platinum­(II) complexes were also structurally characterized by X-ray crystallography, and short intermolecular C–H···Pt contacts were observed. Vibronic-structured emission bands originating from triplet IL (3IL) excited states of the bpzb ligands with mixing of some 3MLCT [dπ­(Pt)→π*­(bpzb)] character were observed in solution state. Interestingly, complex 5 shows a low-energy emission that is derived from the involvement of the p-nitrophenylethynyl ligand. Complex 9 with hydrophobic cholesteryl 4-ethynylphenyl carbamate ligand was found to form stable metallogels in several organic solvents, which are responsive to mechanical sonication and thermal stimuli and show circular dichroism activity.