Tuning Aggregation in Liquid-Crystalline Squaraine Chromophores

For a series of novel hydroxy anilino squaraines (SQ), separated via short flexible spacers from bulky dendrons, hexagonal columnar (Col_hex) liquid-crystalline (LC) phase behavior is detected. The optical properties of these SQ systems, designed for melting below 80 °C, very low for SQ systems, are found to be determined by the LC structures which in turn are governed by volume and steric effects of the dendrons affecting the temperature-dependent interplay between monomeric species and H-aggregates in the LC state, ultimately responsible for the optical properties. Experimental results are corroborated by self-consistent field theory (SCFT) as well as time-dependent density functional theory calculations (TD-DFT). The results demonstrate a new strategy for dynamically tuning aggregates and optical properties for the prescriptive functionalization of the LC SQ materials and with potential for other aggregating systems.