A proton transfer crystal, N,N′ -diphenylguanidinium 3,5-dichlorobenzoate (DPGCB), was synthesized, and single crystals were grown using the slow evaporation solution method. The crystal structure was confirmed via single crystal X-ray diffraction at 25 °C, and results show that the crystal structure was stabilized through N–H…O, C–H…O, and C–H…Cl hydrogen bonding interactions. Hirshfeld surface analysis reveals that the van der Waals H…H (32.3%) contacts play a significant role in crystal packing. Optimized geometry demonstrates the formation of R 2 2 (6) graph set involving N–H…O hydrogen bond. Natural bond orbital (NBO) and Mulliken charge analyses also support the existence of N–H…O hydrogen bonding interactions. Molecular electrostatic potential analysis proves the proton transfer mechanism in the formation of DPGCB. The UV–visible absorption spectrum proves that the absorption at 209 nm is mainly due to the π→π* transition. The time-dependent density functional theory (TD-DFT) analysis of DPGCB reveals that the electronic transition at 247 nm in acetone phase originated from the contribution of π→π* transition bands. DFT predicts that the highest unoccupied molecular orbital–lowest unoccupied molecular orbital(HOMO–LUMO) energy gap is 4.70 eV. The compound is stable up to 200 °C. It is found that the value of the first-order hyperpolarizability of DPGCB is 25times greater than that of urea. The Z-scan study shows that the third-order susceptibility of DPGCB is 1.80 × 10 −6 esu, which is attributable to the strong electron cloud delocalization between two ionic moieties through hydrogen bonding association. © 2019 Elsevier Ltd