A Kinetic Model for Photoswitching of magnetism in the High Spin Molecule [Mo(IV)(CN)2(CN-Cu(II)(tren))6](ClO4)8

TL;DR

This paper presents a kinetic model explaining the photomagnetism in a high-spin molybdenum-copper complex, emphasizing the role of long-lived S=3 states and their kinetics rather than oscillator strength differences.

Contribution

It introduces a kinetic model incorporating internal conversions and intersystem crossings to explain the temperature-dependent photomagnetism in the complex.

Findings

The model fits experimental magnetization data across different irradiation times.

Photomagnetism is governed by kinetics, not oscillator strength differences.

Long-lived S=3 states are key to the observed photomagnetic behavior.

Abstract

The heptanuclear complex [Mo(IV)(CN)2(CN-CuL)6]8+ exhibits photomagnetism. An earlier microscopic model showed that the transition dipole moments for excitation in different spin manifolds are similar in magnitude. In this paper, we attribute photomagnetism to the long lived S=3 charge transfer excited state for which there appears to be sufficient experimental evidence. We model the photomagnetism by employing a kinetic model which includes internal conversions and intersystem crossings. The key feature of the model is assumption of the existence of two kinds of S=3 states: one which has no direct pathway for internal conversion and the other characterized by slow kinetics for internal conversion to the low-energy states. The trapped S=3 state can decay via a thermally activated barrier to the other S=3 state. The experimental temperature dependence of magnetization plot is fitted using rate constants with Arrhenius dependence. The two different experimental cMT vs. T curves obtained with different irradiation times are fitted with our model. Our studies show that the photomagnetism in these systems is governed by kinetics and not due to differences in oscillator strengths for excitation of the different spin states.