Nonlinear Optics (NLO) is significant in scientific research due to its foundational role in optical communication, ultrafast laser pulse generation, optical switching and signal processing, frequency conversion, nonlinear microscopy, Quantum optics and photonic devices. Peptide based molecular materials are very significant in nonlinear optics due to their electronic and luminous properties. Diphenylalanine (FF) is a short peptide that has garnered promising attention due to its unique properties like self-assembly, optical transparency, optical stability and biocompatibility. Diphenylalanine provides a variety of applications in nonlinear optics (NLO) such as second harmonic generation (SHG), third harmonic generation (THG), optical waveguides, nonlinear optical switching, optical data storage and processing. In the present work we design a series of diphenylalanine (FF) based push-pull chromophores in order to check the influence of a set of various electron donors. Here diphenylalanine plays the role of π- spacer and cyano (-CN-) group is the common electron acceptor. Density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods at B3LYP/6-31+G(d) level of theory is used to calculate nonlinear and linear optical properties of designed compounds. The computational study shows that by choosing suitable donor moieties, the designed compounds can be effectively tuned to a better nonlinear optical property.