In the present work, the crystal structure and third-order nonlinear optical (NLO) properties of two novel chalcone derivatives namely (E)-3-(4-bromo2-fluorophenyl)-1-(3,4-dimethoxyphenyl)prop-2-en-1-one (I) and (E)-3-(4-bromophenyl)-1-(3,4-dimethoxyphenyl) prop-2-en-1-one (II) are investigated by analyzing the packing pattern, intermolecular interaction, Hirshfeld surface analysis and standard Z-scan technique with continuous wave laser at 532 nm. Both compounds are donor-acceptor-acceptor (D-A-A) type intramolecular charge transferring molecule which crystallized in centrosymmetric space group. The existence of C-H center dot center dot center dot O hydrogen bonds in I and Br center dot center dot center dot O short contact interactions in II play important roles in their packing pattern and NLO properties. The molecules reveal a strong nonlinear refraction (NLR) and nonlinear susceptibility chi((3)) when the donor and acceptor are arranged side-by-side as in compound I. And as the donor and acceptor are aligned on a head-to-head alignment, the molecules divulge a strong third-order nonlinear absorption (NLA) and limiting threshold (LT). The Z-scan results indicate that both compounds would be potential applicants in the development of NLO devices.