Book excerpt: There is growing need to utilise Earth-abundant transition metal complexes in photovoltaic and photocatalytic applications, while reducing the current heavy reliance on rare, expensive and toxic heavy transition metal complex, such as Ru-based. Iron is the most abundant transition metal within the same group 8 as Ru while being very cheap and eco-friendly. But its photophysics suffers from the disadvantage of short excited-state lifetime of MLCT states due to low lying MC states. However ever since the introduction of NHC carbene-based ligands, the increased sigma donor strength has significantly improved the MLCT lifetimes and there has been a tremendous development in the last decade. This thesis delves into an extensive investigation of the photophysical and photochemical properties of diverse homoleptic and heteroleptic Fe-carbene complexes to unravel the influence of ligand architecture and design on excited-state dynamics. The primary objective of elucidating excited-state dynamics and deactivation pathways in relation to structure-property relationships. Expanding the scope of iron carbene complexes for functional applications is another key goal, achieved by introducing pH-sensitive functional ligands that hold immense significance for light-driven applications.