The development of a robust folded scaffold as a fluorescent material using butylidine-linked pyridazinone-based systems via aromatic pi center dot center dot center dot pi stacking interactions

Fluorescence-capable robust folded pyridazinone-based homo- and heterodimers linked with butylidine linkers, whose crystals exhibit fluorescence with quantum yields of 11% (1CN) and 28% (2CN) due to intramolecular stacking, were synthesized. Previous reports state that intramolecularly folded/stacked compounds result in immediate quenching with no fluorescence, but we have designed two intramolecularly stacked compounds that show suitable emission spectra due to charge transfer between two conjugated heteroaromatic rings. Full spectral profiles and quantum yields of the organic solid-state emitters are reported. The optical behavior of pyridazinone and the triazinone-related homo- and heterodimers was rationalized based on time-dependent density functional theory (TD-DFT) studies, and the observed stacking interactions in crystals were studied in detail. This work demonstrates the significance of cyanoaromatics in the design of solid-state organic fluorescent materials. Herein, we report that the intramolecular folding nature of organic solid-state materials has an important effect on their photophysical and charge transfer properties. Hence, our insights pinpoint the importance of charge transfer between pi-stacked folded dimers.