Experimenting with a magnetic field almost 1M times stronger than that of the Earth, researchers in the Scholes Group were able to modify the optoelectronic properties of model nonmagnetic organic chromophores. The modifications, according to the paper, arise from the induction of ring currents in the aromatic molecules.
For the experiment, researchers chose a model aromatic chromophore called a phthalocyanine, which has a molecular structure similar to chlorophyll -- nature's light absorber -- but with stronger absorption of visible light and higher stability. The calculations on this model phthalocyanine compound and its aggregates showed clear, magnetic field-dependent changes to phthalocyanine's ability to absorb light. These results mark the first to demonstrate magnetic field dependent changes to the absorption spectrum of diamagnetic molecules. But it wasn't until researchers applied the classical analogue of the solenoid that the experiment sharpened into clarity.
A solenoid is an electromagnetic device that effectively converts electrical and magnetic energy using conductive loops of wire arranged like a spring. With their thinking grounded in the behavior of solenoids, Kudisch said, they were able to rationalize that the increased magnetic field sensitivity they were observing in the phthalocyanine aggregates could depend on the relative arrangement of the phthalocyanine rings in the aggregate.
"Not only did this add extra validation to our computational support, but it also lent credence to this idea of coupled aromatic ring currents -- the ring currents of neighboring phthalocyanine chromophores in the aggregate have a geometry dependent on amplification of magnetic field sensitivity," said Kudisch. "Just like the solenoid."
Novel magnetic field effect in diamagnetic molecules -- ScienceDaily
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