Effect of solvent polarity on excited-state double proton transfer process of 1,5-dihydroxyanthraquinone

The excited-state double proton transfer (ES-DPT) properties of 1,5-dihydroxyanthraquinone (1,5-DHAQ) in various solvents were investigated using femtosecond transient absorption spectroscopy and the DFT/TDDFT method. The steady-state fluorescence spectra in toluene, tetrahydrofuran (THF) and acetonitrile (ACN) solvents presented that the solvent polarity has an effect on the position of the ESDPT fluorescence emission peak for the 1,5-DHAQ system. Transient absorption spectra show that the increasing polarity of the solvent accelerates the rate of excited state dynamics. Calculated potential energy curves analysis further verified the experimental results. The ESDPT barrier decreases gradually with the increase of solvent polarity from toluene, THF to ACN solvent. It is convinced that the increase of solvent polarity can promote the occurrence of the ESDPT dynamic processes for the 1,5-DHAQ system. This work clarifies the mechanism of the influence of solvent polarity on the ESDPT process of 1,5-DHAQ, which provides novel ideas for design and synthesis of new hydroxyanthraquinone derivatives.