The effects of (hydrogen/halogen)–edge termination on the structural, electronic, and optical properties of planar SiNRs with either zigzag (ZSiNRs) and armchair (ASiNRs) edges are investigated by means of DFT calculations . The obtained results show that X-edge termination is a new approach to tune and open the band gap in planar SiNRs, and exhibiting a metallic character. The density of states (DOS) analysis reveals a strong hybridization between halogen- p and edges Si- p states, which is not the case of H- s and edges Si- p states. The calculated charge density contours manifest the ionic nature of Si–X (X = H, F, Cl, Br, and I) bonds. However, the Si–Si bonds display a typical covalent bonding feature. The investigation of the optical properties for both polarizations indicates that 7-ASiNR-X and 5-ZSiNR-X exhibit strong optical anisotropy in infrared (IR), visible (VIS), and ultraviolet (UV) regions under both polarizations, making them promising candidates for optoelectronics and optical nanodevices such as polarization-sensitive photodetectors. Besides, for perfect planar ASiNR and ZSiNR, the strong absorbance peak of ε 2 y y ( ω ) has been found to occur at 0.32 (0.36) eV, respectively, suggesting that these compounds may be candidates for IR optoelectronic devices . The most dominant absorption peaks centred at 5.17 and 4.5 eV for ASiNR-H and ZSiNR-H systems, respectively, indicate a high absorbance in the UV range, making them prospective nanomaterials for photovoltaic devices . • The X-edge terminated planar ZSiNRs exhibit a metallic character. • Si–X (X = H, F, Cl, Br, I) bonds manifest an ionic nature whereas Si–Si bonds display a typical covalent bonding. • 7-ASiNR and 5-ZSiNR exhibit a strong optical anisotropy (IR, VIS, UV), hence promising candidates for optoelectronics. • Perfect planar ASiNR/ZSiNR exhibit a strong absorbance peak at 0.32/0.36 eV hence can be used for IR optoelectronic devices. • The high absorbance in UV range makes them prospective nanomaterials for photovoltaic devices.