The term ‘molecular polaritonics’ is used to describe the strong coupling of molecular materials to confined optical fields, and the formation of new hybrid states, termed polaritons, that are a linear superposition between excitons and photons. In the past few years, polaritons have become a readily accessible platform to study fundamental and intriguing phenomenology at room-temperature, with a few realisations among many include Bose-Einstein condensation, access to topological physics and ultralong-range energy transfer. Additionally, it has been recently shown that the excited-state reactivity of molecular materials could be altered in polaritonic systems [1]. One of the most fundamental photophysical reactions in molecular materials is photobleaching; an irreversible event that cause permanent photo-degradation of the organic molecules.  This is particularly important in organic optoelectronic devices because it can cause permanent damage on the devices and limit their operational performance and stability. In recent studies, it was shown that the photobleaching could be suppressed in dye-coated plasmonic nano-structures [2] as well as microcavities filled with P3HT molecules [3] when compared with control films.

Here, we introduce a new microcavity design that allowed the observation and quantification of the photobleaching effect. A shown in Figure 1, we have used the Transfer Matrix Method (TMM) to design and fabricate a series of multilayered optical microcavities containing as an active material the J-aggregated dye TDBC that has been sandwiched between two SiO₂ spacer layers. Following careful design of the thicknesses of the microcavities’ various layers, we have been able to realize structures that operate in either the weak or strong coupling regime while maintaining similar design characteristics. Most importantly, the thickness of the active molecular layer used was between 20 and 30 nm allowing the entire number of molecules to either reside at the node or anti-node of the confined electric field, rather than being distributed along the total volume of the microcavity. Using this approach, we could maximise or fully suppress the cavity effects depending on the selected design.

Optical microcavities have been studied using a k-space imaging technique measuring white-light reflectivity and photoluminescence, with the data being fitted with a standard coupled oscillator model to allow light-matter interaction parameters to be extracted. Next, we have studied the photostability of weakly and strongly coupled microcavities as well as non-cavity control films, through photoluminescence measurements. Following extended laser exposure of the samples, we observed a suppression of the photobleaching rate in strongly coupled microcavities as compared to weakly coupled structures and non-cavity control films.