Macrocyclic Diacetylene-Terthiophene Cocrystal: Molecular Self-Assembly, Topochemical Polymerization, and Energy Transfer

Abstract

The macrocyclic structure offers direction-control self-assembly to generate columnar supramolecular architectures with a guest molecule-accessible interior cavity. Owing to the pi-pi stacking characteristic and photopolymerizable feature of the diacetylenic 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 pi-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 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 by elemental analysis confirms the inclusion of the 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 Forster resonance energy transfer behavior between fluorescent 3T and conjugated PDA polymer. The energy transfer phenomenon observed with the tubular PDA and oligothiophenes should be useful in the design of new energy harvesting functional supramolecules.