We applied (TD)DFT calculations for systematical comprehension of the ESIPT effect in NPDM (Fig. ). The molecular electrostatic potential (MEP) reveals the dispersions of electron density on the molecular surface, is an extremely useful tool for understanding of the H-bonding interaction. So first, the electrostatic potential (ESP) surface of NPDM was calculated to disclose the activity of the hydrogen bond O-H•••N. As shown in Fig. , the electrostatic potentials of DAMN moieties were smaller than that of naphthols, indicating the accumulation of negative charges on the DAMN sites. Besides, the positive potentials of OH groups (H-bond donors) and the negative potentials of N atoms of the -C=N groups (H-bond acceptors) proving the existence of hydrogen bonds in NPDM. Additionally, the frontier molecular orbitals (FMOs) analysis was presented to further certify the existence of the ESIPT phenomenon. Although the electronic distributions over the ESIPT-generated K* form were closely resemble those of E* form, but the transformation from E* to K* form caused a lower energy gap between the HOMO and LUMO by 0.0781 eV (Fig. ). Thus, the diminished energy gap was precisely corresponding to the red-shift of emission maximum for K* form of NPDM. In addition, the IR vibrational spectra were simulated to analyse the variations of Hbonds strength of O-H groups (Fig. ). The comparative observation specified that the IR vibration frequency of O-H in the S1 state showed a significant red shift of 326 cm -1 (from 3188 cm -1 to 2862 cm -1 ), endorsing the the change in the geometric parameter of intramolecular H-bondings and enhancement phenomenon of Hbonds in the S1 state, and implying the happening of ESIPT effect is more favorable. Furthermore, in order to explore the inherent mechanism of the ESIPT effect, the 2D potential energy curves (PECs) of NPDM at the S0(E) and S1(E*) states were scanned separately according to the optimized structures (Fig. ). The obtained PECs of NPDM are as the functions of O-H distance ranging from 0.9972 Å(initial length) to 2.3572 Å and 1.0072 Å(initial length) to 2.2872 Å at its S0 and S1 states respectively. As plotted in Fig. , the forward energy barrier of 3.15 kcal/mol is higher than the reverse energy barrier (0.18 kcal/mol), manifesting that it is of difficulty to occur the proton transfer reaction at the S0 state. By contrast, there is almost no energy barrier in the S1 state proton transfer. Hence, this is more favorable for the ESIPT process to proceed.