Anomalous reflection properties in high density limit fibril shaped PIC-J aggregates in microcavity structure

We report our recent observations on anomalous reflection properties of organic microcavity containing PIC J-aggregates in fibril-shaped structures as one of their highest-density limiting case. Even in ordinary low density PIC-Js dispersed in polymer matrices, they easily go into the exciton-photon strong coupling regime and new quantum states, i.e. exciton-polaritons, are formed. Vacuum Rabi-splitting, an indicator of the coupling strength, can be controlled by the density of PIC-Js in the microcavities in low density regime. Fibril-shaped PIC-J aggregates are bundle-like, self-assembled higher-order structure of Js and are considered as a high-density limiting case. Angular dependence of the local reflection spectra are observed by our improved microscopy. While in the low density cases, clear anti-crossing behaviours of the two branches appear, which is the evidence of the polariton formations, the highest-density limiting cases show one or two anomalous reflection dip structures with almost no angular dependence. The result is inconsistent with neither ordinary polariton reflection property nor bare exciton nor cavity photon properties. We tentatively consider that the anomaly is inherent to the fibril formation and is caused by possible breakdown of polariton coherence due to the inter-fiber energy transfer. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)