Thienothiophene-based quantum dots: calibration of photophysical properties via carbon dot and biomolecular interactions

Semiconductor-based quantum dots (QDs) are size-tunable, photostable and extremely effective fluorophores with strong bandgap luminescence, which make them attractive for biological and medical nano-applications. Herein, we present a thienothiophene (TT)-based highly conjugated fluorescent semiconductor containing triphenylamine (TPA) and tetraphenylethylene (TPE) units, TT-TPE-TPA, as a QD conjugate. As TT-TPE-TPA exhibits remarkable photophysical properties such as a maximum solid-state quantum yield of 47%, a maximum fluorescence solution quantum yield of 81%, a mega Stokes shift of 133 nm and a positive solvatochromism from blue to orange colors, its carbon-nitrogen (CN) and carbon-nitrogen-boron (CNB) dots were prepared. While the dots changed the emission characteristics of TT-TPE-TPA, depending on the enhanced conjugation and fluorescence properties of TT-TPE-TPA/CDs, tunable optical properties were achieved towards vital biomolecules such as urea, NH₄Cl and sucrose. By systematically modulating the composition and concentration of TT-TPE-TPA, CDs, and biomolecules, the detailed mechanisms of energy transfer, fluorescence quenching, and radiation enhancement were revealed. This work opens the door to a new class of promising optical nanomaterials that could be controlled in TT-based QDs.