A first-principles study of the structural diversity and optoelectronic properties of the small penta-graphene (PG) quantum dots (PGQDs) of various sizes is performed. The stability and optoelectronic properties of the PGQDs are investigated under the effects of chemical modifications. PGQDs are edge-functionalized by Si, P, O, and F atoms. Furthermore, PGQDs are also doped with B and P atoms. An increase in the size of the PGQDs leads to a decrease in their bandgaps. All edge-functionalized structures are stable with strong electronic quantization and exhibit semiconducting properties, except for the P-edge functional structure (metallic nature). There is a semiconductor–metal transition with some doped structures. We did not observe absorption peaks in the visible region for hydrogen-passivated PGQDs. However, some absorption peaks appear in this region for edge-passivated or doped PGQDs. There are changes in the electronic properties of PGQD samples containing the impurities B, P, or BP, which also causes a shift in the peak of the spectrum to the visible region from the ultraviolet region of the corresponding pure sample because of various hybridization effects in PG (sp2 and sp3) and PGQDs with edge passivation and atom doping. A solid optical polarization effect occurs with some structures, e.g., H-36-B1P2 and F-ZZ-36. This represents its significant asymmetry and anisotropy compared to the other structures. The enhanced reactivity and the controllable electronic properties by size change, edge passivation, and doping make PGQDs ideal for new nanodevice applications