Double-proton transfer mechanism in 1,8-dihydroxydibenzo[a,c]phenazine: a TDDFT and ab initio study

Theoretical Design of Near-Infrared Fluorescent Sensor for F Anion Detection Based on 10-Hydroxybenzo[h]quinoline Backbone

Proper design and development of near-infrared (NIR) fluorescent sensors is very important for applications in vivo. In this work, we theoretically designed a ratiometric and NIR fluorescent sensor based on the 10-hydroxybenzo[h]quinoline (HBQ) backbone via systematically investigating the substituent effects of electron-donating groups (-NH₂, -CH₃, -C(CH₃)₃) and electron-withdrawing groups (-NO₂, -CN, -F, -Cl, -CF₃) at the proton donor site on the proton transfer process in HBQ in both the S₀ and the S₁ states. According to the calculated potential energy profiles along the proton transfer as well as the photophysical properties among all the derivatives, we successfully screened out that 7NH₂-HBQ is a promising fluorescent sensor exhibiting the near IR emission spectra accompanied by the large Stokes shift. The potential use of 7NH₂-HBQ for F^- detection among anions (F^-, Cl^-, and Br^-) was further studied, and the results showed that 7NH₂-HBQ is very sensitive and selective toward F^- based on the intermolecular hydrogen bonding interaction between F^- and OH bond, forming a new complex FAC_S0 . The ratiometric change in the fluorescence intensity could be induced by the H-F bond transfer from the O atom to the N atom in the S₁ state.

Excited state intramolecular single proton transfer mechanism of pigment yellow 101 in solid state: Experiment and DFT calculation

To investigate fluorescence mechanism of Pigment Yellow 101 (P. Y. 101) in solid state, three aromatic aldehyde azines (1-3) including P. Y. 101 have been synthesized and compared with each other. Results indicated that P. Y. 101 prepared by solvothermal method is actually the mixture of two polymorphs, whose molecular packing mode can be transformed into each other by recrystallizing or external stimuli such as pressure and grinding. The ESIPT properties of 1-3 were investigated by DFT/TD-DFT calculations and time-correlated single photon counting (TCSPC) technique. Both experimental and theoretical results revealed that the dual fluorescence properties of P. Y. 101 in solid state are ascribed to the excited-state intramolecular single proton transfer fluorescence emissions of two structurally different polymorphs rather than the results of the sequential or concerted excited-state intramolecular double proton transfers, which provide a potential valuable tool for developing multistimuli-responsive luminescent materials.

Effects of π-expansion, an additional hydroxyl group, and substitution on the excited state single and double proton transfer of 2-hydroxybenzaldehyde and its relative compounds: TD-DFT static and dynamic study

The effects of π-expansion, an extra hydroxyl group, and substituents on the photophysical properties, the excited state single proton transfer and the double proton transfer of 2-hydroxybenzaldehyde and its relatives have been theoretically investigated using TD-DFT.