Aggregation-induced emission of nitrogenous heterocycle-bridged cyclootatetrathiophene dimers

A series of nitrogenous heterocycle-bridged cyclooctatetrathiophene (COTh) dimers 1–5 bearing pyridyl, pyrimidyl, triazinyl, bipyridyl and phenanthrolinyl spacers were synthesized via Suzuki reactions. The X-ray single-crystal analyses of 1 and 2 show that the nitrogenous heterocycle motifs and their linked thiophene units are coplanar due to the intramolecular S⋯N interaction. The photophysical properties of 1–5 exhibited typical aggregation-induced emission (AIE) property in THF/H2O mixtures, and the aggregates formed with different water fractions were studied by scanning electron microscopy (SEM) and dynamic light scattering (DLS). Thus, the key to increase AIE emission is the favorable crystal packing dominated by intramolecular S⋯N and intermolecular π-π stacking interaction, affecting the molecular conjugation and rigidity to result in strong fluorescence emissions in the aggregation state.