Barrier-free reverse-intersystem crossing in organic molecules by strong light-matter coupling

Abstract

Strong light-matter coupling provides the means to challenge the traditional rules of chemistry. In particular, an energy inversion of singlet and triplet excited states would be fundamentally remarkable since it would violate the classical Hund’s rule. An organic chromophore possessing a lower singlet excited state can effectively harvest the dark triplet states, thus enabling 100% internal quantum efficiency in electrically pumped light-emitting diodes and lasers. Here we demonstrate unambiguously an inversion of singlet and triplet excited states of a prototype molecule by strong coupling to an optical cavity. The inversion not only implies that the polaritonic state lies at a lower energy, but also a direct energy pathway between the triplet and polaritonic states is opened. The intrinsic photophysics of reversed-intersystem crossing are thereby completely overturned from an endothermic process to an exothermic one. By doing so, we show that it is possible to break the limit of Hund’s rule and manipulate the energy flow in molecular systems by strong light-matter coupling. Our results will directly promote the development of organic light-emitting diodes based on reversed-intersystem crossing. Moreover, we anticipate that it provides the pathway to the creation of electrically pumped polaritonic lasers in organic systems.

Microcavity-like exciton-polaritons can be the primary photoexcitation in bare organic semiconductors

“…The formation of EP states in bare organic films could also enhance chemical reactions such as charge transfer 87 or isomerisation 88 in a manner similar to that demonstrated in organic microcavities 1 . Here, the hybrid light–matter excitation would alter the reaction driving force, with the creation of UP/LP states allowing previously thermodynamically or kinetically unfavourable electronic intermediates to be accessed 12 , 89 . The ability to tune the strength of a light-matter interaction, via the refractive index of the environment, could allow these methods to be applied to materials which are challenge to process in microcavities, e.g.…”

Direct and Indirect Chemiluminescence: Reactions, Mechanisms and Challenges

“…To the best of our knowledge, one of the very first examples of direct CL is dated back in 1928 [43], and it is based on the oxidation of luminol by H 2 O 2 (Scheme 1) [44,45]. After luminol's oxidation, a strong blue emission with λ max = 425 nm is recorded through a reverse intersystem crossing (rISC) [46][47][48] that can last from a second up to few hours, depending on the quantity of the reacting species, the presence of specific additives and the "feeding" process. The light emission of luminol and its derivatives can be assisted by catalysts such as peroxidase and heme, which are usually used as additives.…”

Cavity quantum-electrodynamical time-dependent density functional theory within Gaussian atomic basis. II. Analytic energy gradient

“…The formation of polaritonic states has been observed for single molecules in a plasmonic microcavity, 10,11 as well as for many molecules in planar Fabry-Pérot cavities. [12][13][14][15][16][17][18][19][20][21][22][23] The energy of a molecular polaritonic state is dependent on the photonic field, the transition dipole moments of the coupled molecular excited state, and the molecular concentration in the microcavity. This opens excitingly new opportunities, especially through varying molecular concentration, to tune photochemical reaction rates (such as photoisomerization 12 ) and to modulate the S 1 -T 1 energy gaps of fluorescent molecules, [20][21][22] among many other applications.…”

“…[12][13][14][15][16][17][18][19][20][21][22][23] The energy of a molecular polaritonic state is dependent on the photonic field, the transition dipole moments of the coupled molecular excited state, and the molecular concentration in the microcavity. This opens excitingly new opportunities, especially through varying molecular concentration, to tune photochemical reaction rates (such as photoisomerization 12 ) and to modulate the S 1 -T 1 energy gaps of fluorescent molecules, [20][21][22] among many other applications. The latter has been found to be useful for the enhancement of reverse intersystem crossing (rISC) rates, which might improve the quantum efficiency of thermally activated delayed fluorescence molecules for light-emitting diode applications.…”