π-Stacked supramolecular contact ion pairs prohibit quenching and provide control of symmetry in fluorescent dyes.

Cationic chromophores like cyanines and xantheniums are prevalent fluorescent dyes used for imaging and as probes. In non-polar environments, however, electrostatic interactions drive formation of ion pairs with the accompanying anions that may assemble further into aggregates of ion-pairs, strongly affecting and deteriorating photophysical properties. Here, we investigate contact ion pairs and higher order aggregates of cationic fluorophores by leveraging a symmetry-sensitive amino-triangulenium dye (ATOTA+) and its combination with anion-binding macrocycle cyanostar (CS). Absorption, fluorescence, and NMR titrations in non-polar solvents show that cyanostar binds the dye's counter ions (X-) in a stable 2 : 1 sandwich-like anion complex (CS2X-) that prohibits dye aggregation. Fluorescence anisotropy and energy transfer measurements show that ATOTA+ and the CS2X- anion complex form well-defined and tightly π-stacked contact ion pairs resulting in highly increased fluorescence quantum yield and lifetime. These effects are found to be general. Addition of cyanostar to six cationic dyes (rhodamine, cyanine, oxazine, triangulenium and styryl type chromophores) in benzene solutions and polystyrene thin films improves photophysical properties assigned to the supramolecular contact ion-pairs formed between dyes and the cyanostar-anion complex.