Supramolecular Engineering of Narrow Absorption Bands by Exciton Coupling in Pristine and Mixed Solid-State Dye Aggregates

Tunability of functional properties in a continuous manner is desired but challenging to accomplish for organic solid-state materials. Herein, we describe a method for tuning optoelectronic properties of solid-state aggregates with narrow absorption bands. First, we systematically shift the absorption maxima of highly dipolar merocyanine dyes in solution by chemical alterations of their chromophore cores. This leaves their solid-state packing arrangements unchanged, affording similar J- and H-coupled aggregate absorption bands at different wavelengths. Next, mixing these isostructural dyes leads to a spectral fine-tuning of the mixed layers, which could be characterized as crystalline organic solid solutions and utilized in narrowband color-selective organic photodiodes. Finally, we devise a semiempirical model, which explains the observed spectral tuning in terms of the molecular exciton theory. Thus, we demonstrate narrowband absorbing solid-state aggregates spanning the wavelength range of 437–760 nm, whose absorption can be fine-tuned over 40% of the visible light range.

Spectral tuning of absorption properties for color sensing is achieved by design of isostructural compounds and binary mixtures thereof, which self-assemble into identical supramolecular aggregates.