Excited-state intramolecular double proton transfer (ESDPT) has long been a subject of attention due to its crucial role in both fundamental exploration and designing related functional materials. In this work, the static and dynamical characterization from first-principles are performed to reveal the ESDPT mechanism of DHNA-2, a molecule designed based on 1,8-dihydroxy-2-naphthaldehyde (DHNA). The modification could provide easier ESDPT with favorable thermodynamics. More importantly, the DHNA-2 possesses enhanced absorption and fluorescence intensity (Δf >
100 %) due to the additional π-conjunction. Meanwhile, the distinct dual-tautomer emission (Δλ >
90 nm) is observed from the first and second PT products in excited states. The corresponding PT paths are demonstrated by constructing energy profiles and potential energy surfaces in both the ground and excited states. Moreover, we examined the influence of solvents with different polarities on conformational energies and spectra properties. Inspection of infrared spectroscopy, visualization of weak interactions, and bond order calculations indicate that photoexcitation could strengthen the intramolecular hydrogen bonds and promote the ESDPT. The H-bond strengthening mechanism caused by electron rearrangement during photoexcitation is also confirmed through the analyses of frontier molecular orbitals and charge population calculations. Additionally, the dynamic trajectories are shown to be in good agreement with static calculations, revealing the conformational changes associated with PT. Considering the improved photoluminescence and optical sensitivity for solvent polarity, the newly designed DHNA-2 is expected to provide multi-perspective reference for understanding the essence of ESDPT and inspiration for polarity-sensitized molecular design.