<p>The enhanced dimensional confinement in one-dimensional (1D) or quasi-1D platinum selenide (PtSe₂) significantly intensifies quantum confinement and surface effects, leading to distinctive electronic and optical properties. However, the efficient production of high-quality 1D or quasi-1D PtSe₂ through precise control dimensionality and orientation remains a substantial challenge. Herein, we report the first successful synthesis of quasi-1D PtSe₂ structures via a carrier-gas-assisted chemical vapor deposition (CVD) approach. By optimizing the hydrogen concentration, we achieved highly oriented and crystalline quasi-1D PtSe₂, which exhibits exceptional thermodynamic stability along the (110) crystal plane. Electrical characterization reveals that 2D few-layer PtSe₂ exhibits p-type semiconductor properties, while quasi-1D multilayer PtSe₂ displays semimetallic behavior. Due to quantum confinement effects in the quasi-1D system, both materials exhibit similar carrier mobilities. In photodetection at 1550 nm, 2D PtSe₂ exhibits conventional positive photoresponse with a maximum response of 97.0 A/W. In contrast, quasi-1D PtSe₂ demonstrates unique negative photoresponse, achieving a maximum response of 194.2 A/W, attributed to its semimetallic nature and significant surface traps. Temperature-dependent photoresponse measurements at various power levels further confirm that the negative response originates from a defect-assisted photogating effect, the strength of which exhibits significant temperature dependence under high-power illumination. This work not only fills a gap in the synthesis of 1D PtSe₂ but also provides a novel material platform for developing advanced infrared optoelectronic devices.</p>