Green-synthesized single-benzene fluorophores exhibiting room-temperature phosphorescence and solid-state fluorescence for biological and optical applications

Abstract

Single-benzene fluorophores (SBFs) offer a minimalistic access to very small, bright, and electronically tunable emitters via push-pull effects. Herein, we report a green, solvent-free SNAr reaction of tetrafluoroterephthalonitrile (TFTPN) with five aliphatic amines that affords five SBFs in 70 -99% yields without chromatography. These dyes absorb at 400 -476 nm and emit in the range 520 -568 nm, achieving photoluminescence quantum yields of 51 - 68% in solution, up to 84% in polystyrene films, and up to 56% in crystalline form. X-ray crystallography and TD-DFT calculations confirmed their near-planar donor-acceptor geometries and large S₁-T₁ gaps, promoting efficient and fast fluorescence, alongside a polymer-induced exciplex delayed emissive component. Some SBFs crystallize as needle-like crystals that guide light with relatively low optical loss (~0.11 dB mm⁻¹) and can be formulated into tunable hybrid room-temperature-phosphorescent materials in inert matrices for timegated luminescence applications. Live-cell imaging using Arabidopsis thaliana roots demonstrates efficient tissue penetration and distinct staining patterns, highlighting their potential as minimal biolabels. This atom-economical multifunctional platform based on strongly emissive SBFs offers a sustainable blueprint for next-generation luminescent materials in photonic, security, and biological applications.