Theoretical study of solvent effects on the white light emission mechanism of single molecule 4-OH-naphthalimide

[Display omitted] •NapH1 in DMF cannot undergo ESPT process in the presence of intermolecular hydrogen bond.•Due to differences on basicity and pKa values, NapH1 can form deprotonated form in S0 state in DMF rather than in toluene.•The enol* and deprotonated* fluorescence combined to produce near-white-light in DMF.•The single fluorescence in toluene is originated from the original form. Organic white light materials fabricated on the basis of single molecules have applied to manufacture the white light-emitting diodes due to their good photostability and relatively simple material preparation. In this work, the different fluorescence emission mechanisms of the NapH1 in n,n-dimethylformamide (DMF) and toluene are investigated to elucidate the process for generating single-molecule near-white-light. From the analysis of bond lengths and electrostatic potential analysis, the intermolecular hydrogen bond can form in DMF instead of in toluene. From the potential energy curves, it is clear that intermolecular proton transfer is not feasible in either DMF or toluene. Frontier molecular orbitals analysis, the dissociation constants and the vertical excitation energies are used to confirm that NapH1 can undergo the deprotonation process in DMF rather than in toluene. Combined with the calculations of the fluorescence values, only the original structure exists stably in toluene which emits blue fluorescence. And the dual fluorescence peaks of NapH1 in DMF are originated from the enol form and the deprotonated form, interacting jointly to emit near-white light. This work contributes to the investigation and advancement for single-molecule organic white luminescent materials.