Excited-state intramolecular proton transfer (ESIPT) is an important photophysical process, and has wide applications in fluorescent probes, molecular switches, and organic light-emitting materials. The molecule with ESIPT is highly sensitive to its surrounding, such as solvent, and exhibits fruitful fluorescence properties. Theoretical study on the microscopic mechanism of proton transfer in regulating the fluorescence properties of organic molecules is very important. Recently, Yang et al. Yang G, Li Y, He L, et al. 2024 Microchem. J. 198 110044 designed a fluorescent probe (FZ) based on the ESIPT. They observed bimodal emission, strong long-wavelength emission, and weak short-wavelength emission in low-polar, highly polar non-protic and highly polar protic solvents, respectively. To reveal the microscopic mechanisms of these fluorescence properties, in this work, we theoretically investigate the proton transfer processes of the FZ molecule in various solvents including toluene, dichloromethane, ethanol, and dimethyl sulfoxide (DMSO) by using density functional theory and time-dependent density functional theory. Based on polarizable continuum model with the integral equation formalism variant (IEFPCM), the optimized structures are obtained and potential energy curves for proton transfer are scanned by employing the CAM-B3LYP functional with Grimme’s D3 dispersion and 6-31+g(d,p)/6-311+g(d,p) basis. Importantly, the excited-state dynamic behaviors of four intermolecular hydrogen-bonding systems in ethanol solvent are explored by using a super-molecular model. The structures, hydrogen-bonding energies, and interaction region indicator (IRI) analysis show that the strength of the intramolecular hydrogen bond is significantly enhanced upon photo excitation. The potential energy curves indicate that the FZ molecules tend to undergo the ESIPT process in all the solvents. The barriers of proton transfer decrease as the solvent polarity increases. As a result, a dual emission and a strong keto (K*) emission are observed in dichloromethane (low-polar) and DMSO (highly polar non-protic), respectively. In ethanol (highly polar protic), the excited-state behaviors of the four super-molecular systems (FZ-OH1, FZ-OH2, FZ-OH3, FZ-OH4) are quite different. In the FZ-OH1, the ESIPT cannot occur because enol (E*) is more stable than K*. As a result, the FZ-OH1 can produce the E* emission. In contrast, the ESIPT can take place almost barrierlessly in the FZ-OH2, resulting in the K* emission. Interestingly, the FZ-OH3 can undergo stepwise excited-state double protons transfer (ESDPT) between the FZ and ethanol molecules, resulting in a dark state of K*. The hole-electron analysis demonstrates that it is the twisted intramolecular charge transfer (TICT) that quenches the fluorescence of K*. Therefore, the observed weak short-wavelength emission in the ethanol can be ascribed to the E* emission of FZ-OH3. Our work is of great significance in understanding and predicting the photophysical properties of organic molecules in solvents and provides a useful theoretical basis for designing and developing ESIPT-based functional materials.