Thienothiophene-assisted hydrophobic carbon dots: photophysical properties and fluorescent ZIF-8 composites

Abstract

Despite extensive studies on heteroatom-containing carbon dots and CD/ZIF-8 composites, molecularly defined fused sulfur heteroarenes have received little attention as precursors for hydrophobic carbon dots. Consequently, the relationship between precursor-derived sulfur environments, excited-state dynamics, and subsequent integration into porous crystalline hosts remains poorly defined. Herein, thienothiophene (TT) was used as a molecular co-precursor in a matched solvothermal synthesis with toluene-derived carbon dots (To-CDs) serving as a control. TT-assisted synthesis produced quasi-spherical carbon dots with closer average interlayer packing and distinct sulfur-containing bond environments. FTIR difference analysis and high-resolution C 1 s and S 2p XPS identified TT-derived thiophene and CS signatures together with reduced C–S–C and oxidized‑sulfur environments. These structural changes shifted the emission from blue region toward green and produced fluorescence decay dynamics longer than those of molecular TT but shorter than those of To-CDs. Subsequent ZIF-8 crystallization in the presence of preformed TT-CDs generated a washed, green-emissive crystalline composite that retained the ZIF-8 diffraction pattern while showing a substantial decrease in N₂-accessible BET surface area. By separating TT-induced carbon-dot differentiation from porous-host formation, this precursor-to-host strategy establishes a direct connection between molecular precursor chemistry, carbon-dot photophysics, and integration into an emissive microporous solid.