Synthesis and Properties of Co-assembled Functional Macrocyclic Diacetylenes

Abstract

Supramolecular tubular structures formed by self-assembly of small organic molecules were importantly utilized in the boundaries of chemical and materials sciences. Because of the structural foundation through noncovalent bonds, conventional tubular architectures frequently lack stability upon exposure to external perturbations. In this dissertation research, covalently bonded chromogenic organic nanotubes were prepared using topochemical polymerization of self-assembled macrocyclic diacetylenes (MCDAs). Additional functionalities were adopted to MCDAs using two types of co-assembly approaches, host¬–guest interaction and metal-ligand coordination. The macrocyclic structure offers direction-control self-assembly to generate columnar supramolecular architectures with the guest molecule-accessible interior cavity. Owing to the π–π stacking characteristic and photopolymerizable feature of diacetylene template, macrocyclic diacetylenes (MCDAs) have emerged as an intriguing molecular design for constructing arrays of covalently connected nanochannels. The energy transfer mechanism by engineering host-guest cocrystals of self-assembling π-electron rich motifs has been widely accepted for devising organic electronics. A highly fluorescent and polymerizable cocrystal of macrocyclic diacetylene-terthiophene (MCDA-3T) was constructed. Single-crystal X-ray diffraction analysis reveals a well-ordered columnar assembly of MCDA with stacking geometry close-to-ideal packing parameters preferred for the topochemical polymerization. Inspection of the extended crystal packing pattern and elemental analysis confirms the inclusion of 3T guest in outer space positioned along the parallel-packed MCDA columns, resulting in an array of nanochannels. UV-induced polymerization of MCDA-3T cocrystal transforms into covalently cross-linked PDAs and displays Förster resonance energy transfer behavior between fluorescent 3T and conjugated PDA polymer. The metal-mediated self-assembly process offers well-directed and controlled construction of supramolecular architectures, and the assembled metal-ligand complex displays diverse functionalities depending on the composition of the complex template. Through a deliberate introduction of a metal-binding nucleobase, cytosine, to the macrocyclic diacetylene (MCDA), a macrocyclic ligand CytMCDA was synthesized. On account of the metal affinity of cytosine and the π–π interaction of diacetylene template, a Hg-coordinated unidirectional columnar self-assembly of CytMCDA was generated forming into organic nanotubes. The monomeric CytMCDA-Hg is covalently cross-linked into blue-phase macrocyclic polydiacetylene nanotubes (CytMCPDA-Hg) via UV-induced topochemical polymerization. CytMCPDA-Hg displayed a naked-eye detectable sensing response with a brilliant blue–to–red chromatic transition toward heat and solvents. Moreover, owing to the high affinity of mercury complex toward sulfur, CytMCPDA-Hg displayed high sensitivity against thiols. The observations and information achieved in this research would provide the understanding and possibility of practical applications of stimuli-responsive macrocyclic polydiacetylene nanotubes.