Transition metal complexes (TMCs) have long been utilized in medicinal chemistry for a variety of therapeutic applications, including anticancer and antimicrobial treatments, due to their rich excited-state properties. Particularly, TMCs that enable selective ligand release have proven highly effective in drug delivery systems. One class of these ligands includes gasotransmitters-small molecules such as nitric oxide (NO) and carbon monoxide (CO). Several TMCs have been developed as tools for releasing these small molecules for therapeutic purposes. For instance, rutheniumand iron-based complexes are used for NO release, while rhenium-and manganesebased complexes are employed for CO release. A major global threat today is antimicrobial resistance (AMR), which is projected to result in 10 million deaths annually by 2050, alongside a reduction in global economy by 2% to 3.5%, costing the world up to $100 trillion. One promising approach to combat AMR is through the use of CO, a gasotransmitter with known antimicrobial properties, which has been studied as a potential treatment for infectious diseases. Recently, photoactivatable carbon monoxide releasing molecules (PhotoCORMs) have been suggested as a new synthetic class of antimicrobials to fight against AMR, such molecules enable spatial and temporal control of CO release process. In recent times, computational chemistry has been employed to model such PhotoCORMs. As for emission and singlet oxygen generation triplet metal-toligand charge-transfer ( 3 MLCT) state is involved and CO-dissociation takes place via the MC state (as shown in Scheme1). Computational studies have provided highly illuminating results for modeling MLCT state 27,28 and 3 MC state. Especially, in the case of the MC state, where the potential energy surface of the lowest triplet state is highly complex, consisting of multiple local minima corresponding to MC states with varying geometric configurations. These studies suggest that the lowest triplet state potential energy surface of such complexes presents a highly intricate landscape, consisting of local minima corresponding to multiple MC states with varying geometric features. Furthermore, the 3 MC state has been predominantly studied in Ru(II)-based complexes, while the investigation of the 3 MC state in Re(I) complexes remains limited. Therefore, in this work, we will focus primarily on exploring the 3 MC state in Re(I) complexes, as it plays a key role in dictating the photochemical pathways and ultimately governs the efficiency of ligand photorelease. Scheme1: Single-oxygen generation and CO-dissociative mechanism in Re(I) complex.