Rainer Herges, from Kiel University's Otto Diels Institute for Organic Chemistry, will deliver a seminar entitled "Molecular Spin Switching." Hosted by Dirk Trauner.
For more information about the speaker, click here.
Abstract: Spin switching (such as spin crossover) under ambient conditions used to be a typical solid state process. We recently developed the first molecular, magnetically bistable systems. Since spin switching in isolated molecules is a new phenomenon, there are a number of unprecedented applications. Molecular spin switches can be used as contrast agents for functional imaging in MRI. We developed a molecular machine type spin switch to measure absolute temperatures in 3D with a resolution of 100 µ and an accuracy of ~0.1°C in a 7T MRI scanner. We are aiming at tuning the properties of our spin switches to detect sites of high metabolic activity, such as inflammations and metastases.
Controlled switching of the spin state of transition metal ions, particularly of Fe2+ and Fe3+ is essential to achieve selectivity and catalysis in a number of metalloenzymes. We report on an iron(III) porphyrin with a photochromic axial ligand which, upon irradiation with two different wavelengths reversibly switches its spin state between low-spin (S=1/2) and high-spin (S=5/2). Conversion is almost quantitative in both directions at room temperature. The system is neither oxygen nor water sensitive, and no fatigue was observed after more than 1000 switching cycles. Concomitant with the spin-flip is a change in redox potential by 60 mV. Our system thus can be viewed as a simple model for the first step of the cytochrome P450 catalytic cycle.