Coordination-Driven Self-Assembly
of 2D-Metallamacrocycles
Using a New Carbazole-Based Dipyridyl Donor: Synthesis, Characterization,
and C<sub>60</sub> Binding Study
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Abstract
A new carbazole-based 90° dipyridyl donor 3,6-di(4-pyridylethynyl)carbazole
(<b>L</b>) 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 <b>L</b> with
several Pd(II)/Pt(II)-based 90° acceptors (<b>1a</b>–<b>1d</b>) yielded [2 + 2] self-assembled metallacycles (<b>2a</b>–<b>2d</b>) under mild conditions in quantitative yields
[<b>1a</b> = <i>cis</i>-(dppf)Pd(OTf)<sub>2</sub>; <b>1b</b> = <i>cis</i>-(dppf)Pt(OTf)<sub>2</sub>; <b>1c</b> = <i>cis</i>-(tmen)Pd(NO<sub>3</sub>)<sub>2</sub>; <b>1d</b> = 3,6-bis{<i>trans</i>-Pt(CC)(PEt<sub>3</sub>)<sub>2</sub>(NO<sub>3</sub>)}carbazole]. All these macrocycles
were characterized by various spectroscopic techniques, and the molecular
structure of <b>2a</b> was unambiguously determined by single
crystal X-ray diffraction analysis. Incorporation of ethynyl functionality
to the carbazole backbone causes the resulted macrocycles (<b>2a</b>–<b>2d</b>) to be π-electron rich and thereby
exhibit strong emission characteristics. The macrocycle <b>2a</b> has a large internal concave aromatic surface. The fluorescence
quenching study suggests that <b>2a</b> forms a ∼1:1
complex with C<sub>60</sub> with a high association constant of <i>K</i><sub>sv</sub> = 1.0 × 10<sup>5</sup> M<sup>–1</sup>
