Carbocyanine dyes are a class of organic compounds that possess two nitrogen containing heterocycles that act as electron donors and acceptors connected by a conjugated methine bridge. This thesis will present the synthetic methodology of symmetrical and unsymmetrical trimethine cyanine dyes in three chapters. The first chapter is a review on the synthesis and application of unsymmetric cyanine dyes. The second will describe the synthesis of unsymmetrical trimethine cyanine dyes and how their optical properties differ from symmetrical dyes. The third chapter will not only discuss the synthetic procedure for synthesis of symmetrical trimethine cyanine dyes, but also will show how varying the N-alkyl substituents and hydrophobicity of the heterocycles affects the dyes interaction with and ability to be used as inhibitors for protein arginine methyltransferases (PRMTs). Several synthesized compounds have displayed lower IC₅₀ values for the inhibition of PRMT1 and PRMT5 comparable to that of current inhibitors.