Magnetoexcitonic Effects on Organic Semiconductors at High Magnetic Fields Probed by Ultrafast Spectroscopy

KUDISCH, BRYAN; MAIURI, MARGHERITA; MORETTI, LUCA; OVIEDO, MARÍA BELÉN; WANG, LEON; PRUD?HOMME, ROBERT K.; STEPHEN MCGILL,; GREGORY D. SCHOLES

Congreso; The 29th International Con- ference on Photochemistry; 2019

Molecular organic semiconductors are an important subset of the emerging field of organic electronics which serve to bothcomplement and improve upon state-of-the-art inorganic semiconductor technologies. For organic optoelectronic applications, it isparamount that we understand how these organic materials interact with light to the extent to which we can predict, design, andoptimize new molecular building blocks to improve device performance. The photophysical properties of these systems, though, areheavily dependent not only on the electronic architecture on the molecular level, but also the degree of electronic coupling betweenneighboring molecules. This interplay gives rise to the outstanding issue in the comprehension of organic semiconductor photophysics:experiments that attempt to establish cause-effect relationships are undermined because of the inability to selectively perturbelectronic structure without affecting intermolecular interactions. Here we show using steady state and ultrafast optical spectroscopiesthat magnetic fields as high as 25 T explicitly modulate the electronic properties of model phthalocyanine (Pc) aggregates. We deducethat this novel magnetic field effect arises from the interaction between the magnetic field and the orbital angular momentum of themolecular wavefunctions through the generation of coupled ring currents in the Pc π-system, manifesting experimentally as a magneticfield-dependent optical cross-section and intersystem crossing rate in CuPc nanoparticles. Our findings suggest that high magneticfields can be used as a powerful and general tool for establishing direct cause-effect relationships between the electronic structure andthe optoelectronic properties of organic materials.