Transition metal dichalcogenides (TMDs), a class of two-dimensional (2D) materials, are proposed to be the next generation materials for optoelectronic, spintronic, and valleytronic devices due to their direct semiconducting bandgap, strong spin-orbit coupling and non-equivalent K points in momentum space. However, pristine TMDs fall short for these purposes due to their fixed band gap and low life times of intrinsic excitons. From a materials design perspective, alloying and heterostructure formation with TMDs are some of viable solutions. The first part of this thesis discusses TMDs design for optoelectronics and valleytronics. For optoelectronic applications, multicomponent alloying is used: different strategies like binary, non-isomorphous quaternary, and isomorphous quaternary alloying have been adopted. For valleytronics, the focus is on tuning the long-lifetime interlayer (IL) excitons present in vertical 2D heterostructures by straining and twisting. The second part of this thesis details the synthesis and emergent properties of a bulk binary chalcogen alloy (S-Se). Combining insulating S and Se results in the formation of a flexible alloy with very high dielectric constant and strength. It is believed that this S-Se alloy could perfectly bridge the gap between conventional brittle ceramics and flexible polymers.