Fig. 1. Structural characterisation of quasi-one dimensional organic semiconductors studied and experimental evidence for light-matter coupling.

a Cartoon and scanning electron-microscopy (SEM) image of PDA. The polymer chains consist of a single-double-single-triple bonded back bone and are near perfectly aligned in 100 μm² domains. Scale bar is 10 μm. b Molecular packing and transmission electron-microscopy image of PIC nanotubes. The cyanine based monomers pack in a brickwork pattern to form nanotubes. They are embedded in a rigid sucrose-trehalose matrix and tend to be highly bundled in films; scale bar 100 nm. c PDI molecules pi-face stack in a quasi-H-aggregate fashion and in four distinct blocks (black outlines) to form ~100 μm long, 50 nm wide nanobelts; scale bar 250 nm. d Absorption (light blue) and specular reflection (dark blue) spectra of PDA. Zooming into the zero-phonon peak at 1.965 eV (right) shows it is split by ~18 meV (Ω) into two branches, an upper (UP) and lower polariton (LP). e Absorption (maroon) and specular reflection (red) spectra of PIC. The excitonic peak at 2.132 eV is split by ~40 meV due to the formation of exciton-polaritons (right). f Angle resolved reflectivity for PIC. Solid red and black lines highlight angle-dependent dips below and above the excitonic transition (dashed line), respectively. The energy of the dips as a function of angle (adjacent) reveals the typical anti-crossing behaviour of strong coupling between a cavity photon-mode and an excitonic transition (dashed line).