Significant Enhancement of Two-Photon Excited Fluorescence in Water-Soluble Triphenylamine-Based All-Organic Compounds.

Understanding water-soluble and environmentally friendly two-photon absorption (TPA) molecules benefits the design of superior organic complexes for biomedical, illumination, and display applications. In this work, we designed two triphenylamine-based all-organic compounds and explored the mechanism of enhanced TP fluorescence in water solutions for potential applications. Experimentally, we showed that adding protein into our TPA molecule solution can drastically boost the TP fluorescence. Numerical simulations reveal that the TPA molecules prefer to dock inside the protein complex. We hypothesize that the interaction between our triphenylamine-based all-organic compounds and water molecules lead to non-radiative decay processes, which prevent strong TP fluorescence in the water solution. Therefore, the protection by, for example, protein molecules from such interactions can be a universal strategy for superior functioning of organic TPA molecules. Further experiments and numerical simulations support our hypothesis. The present study may facilitate the design of superior water-soluble and environmentally friendly superior organic complexes.

Enhanced Two-Photon Absorption in Two Triphenylamine-Based All-Organic Compounds.

Two-photon absorption (TPA) enables the excitation of molecules by comparatively lower energy photons with longer penetration depth and higher spatial precision control, which advances the uses of organic molecules in various applications. In this work, we report two simple all-organic molecules C42H33N (compound 3) and C138H168N4 (compound 14) with strong TPA and fluorescent emission activity. Density functional theory calculations show that the enhanced oscillator strengths could be responsible for improved TPA and emission activity for compound 14 compared to those for 3. The degradation of C138H168N4 under focused laser illumination without circulation is almost negligible within 5 h, making it a candidate for laser dyes. Solid-state measurements confirm the presence of a direct band gap for electron transition that determines the channel to release the absorbed energy and functionality of the studied molecules. This work emphasizes that a high TPA cross-section and selectable energy relaxation (fluorescent emission or heat dissipation) are equally important to the design of advanced functional TPA molecules.