In this work, we designed series of indolo[3,2,1-jk] carbazole based donor-pi-acceptor organic dyes S1-S8 by modifying the pi-bridge of experimentally synthesized dye IC-2 in order to evaluate their potential nonlinear optical (NLO) properties. Density functional theory (DFT) calculations with B3LYP/6-31 + G(d,p) level of theory was used to shed light on how bridging core modification affect the charge transport, electronic and NLO properties of Sl-S8? Time-dependent DFT (TDDFT) computations using B3LYP, CAM-B3LYP, WB97XD and M062X functional were performed to examine photophysical properties. Results indicate that HOMO-LUMO energy gaps in Sl-S8 (3.03-2.61 eV) were found smaller than IC2 (3.11 eV) which results in large NLO response and obvious red shifts than IC2. Natural bond orbital (NBO) analysis reveals that separation of charge is formed and electrons are successfully moved from donor to acceptor unit. Sl-S8 showed absorbance wavelength in the visible region (388-436 nm) and greater than IC2 (386 nm). An enhanced NLO response was observed in Sl-S8 as compared to IC2. Interestingly, S7 exhibits appealingly large enhancement in NLO response properties with < alpha > and beta(tot) computed 512 (a.u) and 39,664 (a.u) respectively. Hopefully, this theoretical investigation will serve as a springboard for the future experimental studies of these NLO dyes.