CASPT2 Potential Energy Curves for NO Dissociation in a Ruthenium Nitrosyl Complex

Abstract

Ruthenium nitrosyl complexes are fascinating photoactive compounds showing complex photoreactivity, such as N→O linkage photoisomerism and NO photorelease. This dual photochemical behavior has been the subject of many experimental studies in order to optimize these systems for applications as photoswitches or therapeutic agents for NO delivery. However, despite recent experimental and computational studies along this line, the underlying photochemical mechanisms still need to be elucidated for a more efficient design of these systems. Here, we present a theoretical contribution based on the calculations of excited-state potential energy profiles for NO dissociation in the prototype trans-[RuCl(NO)(py)4]2+ complex at the complete active space second-order perturbation theory (CASPT2). The results point to a sequential two-step photon absorption photorelease mechanism coupled to partial photoisomerization to a side-on intermediate, in agreement with previous density functional theory calculations.

Metalloligand-based coordination polymer embedding the nitrosyl ruthenium complex for photoactive materials with bound nitric oxide

“…From that point, the complex can relax back to the GS linear geometry or can relax to the side-coordinated metastable state (MS2) of the nitrosyl group which is a local minimum on the electronic ground state PES. 45,46 Similarly, the excitation of the MS2 state leads to the excited states which are displaced from the minima of the electronic ground state PES in terms of the M–N–O angle. One of these excited states is the recently visited N -coordinated bent nitrosyl state and another one is the O -coordinated counterpart.…”

Recent advances in photorelease complexes for therapeutic applications

“…photorelease is a sequential two-photon process coupled with partial photoisomerization of the nitric oxide ligand. 44 This twophoton mechanism should certainly be considered for the ruthenium(II) polypyridyl nitrosyl examples illustrated in Fig. 5.…”

“…Interestingly DFT theoretical calculations (CASPT2) using trans -[Ru(Cl)(NO)(py) 4 ] 2+ , where py = pyridine, supports that NO˙ photorelease is a sequential two-photon process coupled with partial photoisomerization of the nitric oxide ligand. 44 This two-photon mechanism should certainly be considered for the ruthenium( ii ) polypyridyl nitrosyl examples illustrated in Fig. 5.…”

Photoinduced linkage isomers in a model ruthenium nitrosyl complex: Identification and assignment of vibrational modes

“…In this context, we recall that the mechanism of the MS1 formation using blue light irradiation can be described as a consecutive reaction involving two excitation-relaxation steps and thus involving two photons GS→MS2→MS1, where the MS2 is an intermediate state [23,66]. The mechanism was extensively studied theoretically, where it was shown that this reaction is rather a multistep excitation-relaxation process, which involves several nonadiabatic intersystem crossing processes between the singlet and triplet states of all three involved isomers GS, MS2, and MS1 [67][68][69][70]. Furthermore, it was reported that the mechanism of NO release in solutions might also involve the formation of the linkage isomers MS2 and MS1 [6,15,16].…”