Making Dark Isomers Bright

Article published in Science Advances.

Polaritons are hybrid light-matter excitations that can form when material excitations are sufficiently strongly coupled to confined light modes in optical cavities. Polaritons in organic systems have shown the potential to modify chemical properties and to mediate long-range energy transfer between individual chromophores, among other capabilities. Thanks to an experiment-theory collaboration between the group of Prof. Vinod Menon at City College of New York and IFIMAC researchers Francisco J. Garcia-Vidal and Johannes Feist, it has been demonstrated that strong coupling and formation of organic exciton-polaritons can be also used to selectively tune the light emission of organic molecules to come from a specific isomer. Molecular isomers are formed by different arrangements of the same atoms in space. By taking advantage of the delocalized and hybrid character of polaritons, their emergence in the strong coupling regime opens a new relaxation pathway that allows for an efficient funneling of the excitation between the molecular isomers. The researchers have implemented this idea by strong coupling to trans-DCS (E-4-dimethylamino-4′cyanostilbene) molecules, which present two isomers when immersed in a polymer matrix, with the relative amount being controllable by the molecular concentration. Under normal conditions, the non-planar (NP) isomer is in the minority and does not contribute significantly to emission. Within the cavity, the new relaxation pathway opened by polariton formation allows to selectively funnel the photoexcitation from a common polaritonic mode (the lower polariton LP) to the excited states of the NP isomer, leading to pure emission from this isomer. This approach thus provides a pathway to significantly modify the emission wavelength of a molecular material, which could be useful for the design of novel light-emitting devices. [Full article]

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