Theoretical investigation of [Ru(bpy)2(HAT)]2+ (HAT=1,4,5,8,9,12-hexaazatriphenylene; bpy=2,2′-bipyridine): Photophysics and reactions in excited state

In this article, Density Functional Theory based calculations, including dispersion corrections, PBEO (D3BJ)/Def2-TZVP(-f), were performed to elucidate the photophysics of the [Ru(bpy)(2)(HAT)](2+) complex in water. In addition, the thermodynamics of the charge and electron transfer excited state reactions of this complex with oxygen, nitric oxide and Guanosine-5'-monophosphate nucleotide (GMP) were investigated. The first singlet excite state, S-1, strongly couples with the second and third triplet excited states (T-2 and T-3) giving rise to a high intersystem crossing rate of 6.26 x 10(11) s(-1) which is similar to 10(6) greater than the fluorescence rate decay. The thermodynamics of the excited reactions revealed that all electron transfer reactions investigated are highly favorable, due mainly to the high stability of the triply charged radical cation (PS)-P-2.(3+) species formed after the electron has been transferred. Excited state electron transfer from the GMP nucleotide to the complex is also highly favorable (Delta G(sol) = -92.6 kcal/mol), showing that this complex can be involved in the photooxidation of DNA, in line with experimental findings. Therefore, the calculations allow to conclude that the [Ru(bpy)(2)(HAT)](2)(+) complex can act in Photodynamic therapy through both mechanisms type I and II, through electron transfer from and to the complex and triplet-triplet energy transfer, generating ROS, RNOS and through DNA photooxidation. In addition, the work also opens a perspective of using this complex for the in-situ generation of the singlet nitroxyl ((NO)-N-1 ) species, which can have important applications for the generation of HNO and may have, therefore, important impact for physiological studies involving HNO. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this article, Density Functional Theory based calculations were used to investigate the photophysics of the [Ru(bpy)(2)(HAT)](2+) complex in water, as well as the thermodynamics of its reactions with oxygen, nitric oxide, and GMP nucleotide. The results showed that the excited state reactions and electron transfers are highly favorable, indicating that the complex can be involved in the photooxidation of DNA and act as a photosensitizer in photodynamic therapy. The study also suggests the potential use of the complex for the generation of singlet nitroxyl and its impact on physiological studies involving HNO.