Panchromatic Absorption of Unsymmetrical Donor-Acceptor Dyes Based on a Meta-Conjugated 1,3,5-Heteroaryltriazine Core

Attachment of three different heterocycles with electron donor or acceptor character to a central 1,3,5-triazine core generates readily soluble side-chain free dyes with two displaying soft crystalline mesomorphism and one displaying a nematic liquid crystal phase as confirmed by polarized optical microscopy, calorimetry, gravimetric analysis, and powder X-ray diffraction. Equally intriguing is the dyes' relatively strong electronic communication between donor and acceptor subchromophores that are meta-conjugated to one another, which is experimentally observed as a broad intramolecular charge-transfer absorption that can extend over 100 nm past the most intense absorption event and is computationally confirmed through density functional theory (DFT) evaluations of the molecular ground- and excited-state properties. This molecular design permits the preparation of dyes with panchromatic absorption not just based on the additive absorption of individual subchromophores.