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.

José Geraldo M Castro Júnior, Willian R Rocha

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy 2022 Apr 05

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In this article, Density Functional Theory based calculations, including dispersion corrections, PBE0(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, S1, strongly couples with the second and third triplet excited states (T2 and T3) giving rise to a high intersystem crossing rate of 6.26 × 1011 s-1 which is ∼106 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 2PS•3+ species formed after the electron has been transferred. Excited state electron transfer from the GMP nucleotide to the complex is also highly favorable (ΔGsol = -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 (1NO-) species, which can have important applications for the generation of HNO and may have, therefore, important impact for physiological studies involving HNO. Copyright © 2022 Elsevier B.V. All rights reserved.

Citation

José Geraldo M Castro Júnior, Willian R Rocha. 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. Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy. 2022 Apr 05;270:120817