Liquid-crystalline ordering of davydov-split aggregates of cyanine dyes

Abstract

3,3′-ditetradecyloxacarbocyanine (DiOC14(3)) and 3,3′-Dioctadecyloxacarbocyanine (DiOC18(3)) are lipophilic carbocyanine dyes with a conjugated polymethine backbone and two long hydrocarbon tails. In this paper, we report the formation of Davydov-split aggregates of DiOC14(3) and DiOC18(3) in methanol/water mixtures with and without ammonia, which show a blue-shifted H-band and a red-shifted J-band with respect to the monomer band in their UV–vis absorption spectra. The Davydov-split aggregates of DiOC14(3) show a fiber-like morphology in the absence of ammonia and a vesicle-like morphology in the presence of ammonia. While the Davydov-split aggregates of DiOC18(3) show a vesicle-like morphology with the different lamellarities, depending on the presence of ammonia in the methanol/water mixtures. These Davydov-split aggregates with different morphologies are birefringence when being viewed through crossed polarizers, suggesting that they have liquid-crystalline phases. The Davydov-split aggregate fibers and vesicles with liquid-crystalline phases and unique excitations are great potential for photonic applications because the liquid-crystalline order and molecular exciton are synergized.