Polymorphism-dependent fluorescence, a phenomenon in which a compound shows various fluorescence properties among its polymorphs, contributes to understanding the relationship between the crystal structure and solid-state fluorescence properties. Here we report that a variety of solid-state fluorescence efficiency by benzyl groups based on polymorphs in an organic pyrazine dye where the polymorphs showed quite different fluorescence efficiency (fluorescence quantum yield: 14% vs 64%) despite their similar molecular conformations and packing motifs in the crystal structures. Crystal structure analysis and optical measurements revealed local loose packing caused by the benzyl groups, which are not a part of the pyrazine fluorophore, greatly influenced fluorescence efficiency in the polymorphs. This result showed that a benzyl substituent can be used as an effective molecular modification for tuning solid-state fluorescence efficiency.
The optical properties of 2,5-diamino-3,6-dicyanopyrazine derivatives bearing singly methyl-or halogen-substituted benzyl groups were studied in both solution and crystalline phases. In solution, all derivatives showed similar absorption and fluorescence properties, since the electronic state of their fluorophore was not altered by substituents attached to the benzyl groups. In contrast, crystalline compounds exhibited a variety of fluorescence colours (yellow, orange, and red), since their solid-state absorption and fluorescence properties were correlated with a change in the electron-donating ability of amino groups due to crystallisation. The absolute fluorescence quantum yields of crystalline dyes (0.14−0.91) showed broad variability, depending on the nature and positions of terminal substituents.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.