**Abstract**

Carbenes are highly reactive intermediates in organic synthesis. These divalent carbon species are generally transient in nature and cannot be isolated. However, they can form stabile metal complexes. Later on, the development of N-heterocyclic carbene (NHC) and other stable carbene led to the application of these carbon (II) donor ligands in the synthesis of complex natural products, transition metal catalysis, organo-catalysis and several other synthetic methodologies. Here in this short review, we will discuss the brief history of the development of carbenes, synthesis of stable carbenes (NHC in particular), and their applications in natural products synthesis transition metal chemistry/organometallics. In addition to synthesis and application, the chapter will consist of a detailed structural analysis of carbenes and exciting photophysics of this class of compounds. Special emphasis will be given to electronic structure. The role of carbene in the development of luminescent NHC transition metal complexes, the tuning of emission properties as well as their active role as photocatalysts in the reduction of CO2 will also be discussed.

**Keywords:** carbene, N-heterocyclic carbene, electronic structure, photophysics, applications
