Coordination-Driven Self-Assembly of 2D-Metallamacrocycles Using a New Carbazole-Based Dipyridyl Donor: Synthesis, Characterization, and C₆₀ Binding Study

A new carbazole-based 90° dipyridyl donor 3,6-di­(4-pyridylethynyl)­carbazole (L) containing carbazole-ethynyl functionality is synthesized in reasonable yield using the Sonagashira coupling reaction. Multinuclear NMR, electrospray ionization-mass spectrometry (ESI-MS), including single crystal X-ray diffraction analysis characterized this 90° building unit. The stoichiometry combination of L with several Pd­(II)/Pt­(II)-based 90° acceptors (1a–1d) yielded [2 + 2] self-assembled metallacycles (2a–2d) under mild conditions in quantitative yields [1a = cis-(dppf)­Pd­(OTf)2; 1b = cis-(dppf)­Pt­(OTf)2; 1c = cis-(tmen)­Pd­(NO3)2; 1d = 3,6-bis­{trans-Pt­(CC)­(PEt3)2(NO3)}­carbazole]. All these macrocycles were characterized by various spectroscopic techniques, and the molecular structure of 2a was unambiguously determined by single crystal X-ray diffraction analysis. Incorporation of ethynyl functionality to the carbazole backbone causes the resulted macrocycles (2a–2d) to be π-electron rich and thereby exhibit strong emission characteristics. The macrocycle 2a has a large internal concave aromatic surface. The fluorescence quenching study suggests that 2a forms a ∼1:1 complex with C60 with a high association constant of Ksv = 1.0 × 105 M–1.