It is envisaged that the dynamic intramolecular motions and relevant vibronic coupling in RT solution could hamper ESIPT. Therefore, to decipher the fluorescence mechanism in RT solution, the PESs of the rotational C=N bond/C=C bond in the enol and keto form respectively in the S1 states were firstly calculated by scanning the torsion angle (0 o →180 o ) at 10 o intervals (Fig. ). Theoretically, the conical intersection (CI) is one of nonradiative pathways and is detrimental to strong light emission with high quantum yield. In addition, the dwindling energy gaps between S1 and S0//S1 (the vertical projected S0 state) can cause an elevated rate of IC (internal conversion) and ultrafast nonradiative decay in terms of the energy-gap law. As described by the excitation state double-bond rotations-guided PESs (potential energy surfaces), twisting around the imino/vinyl-double bond can yield the CI at the 90 o torsional angle. These imply that the excited NPDM molecule can be efficiently inactivated to S0//S1 state via the CI pathway of nonradiative IC, after that the vibrational relaxations to their original S0 states or isomers. The total de-excited processes are defined as PIND. It is noteworthy that the excited NPDM molecule (E* and K*) exhibits the double bond twisting behaviors, resulting in the vain overlap of molecular orbitals with f = 0 in the emissive transitions, which caused that the NPDM molecule has almost no fluorescence in RT solution. Thus, the rotations of doublebond could explain the special emission behaviors of the tweezers NPDM. Obviously, the weak emissions of NPDM in aqueous DMSO were mainly owing to the ease of C=N bond/C=C bond rotation in the S1 states.