Optical spectroscopy of a polyfluorene copolymer at high pressure: intra- and intermolecular interactions.

We present optical spectroscopy studies of the conjugated polymer poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) at high pressure. The photoluminescence spectrum of F8BT in a dilute solid-state solution in polystyrene redshifts by 320 meV over 7.4 GPa, while that of a F8BT thin film redshifts 460 meV over a comparable pressure range. We attribute the redshift in solution to intrachain pressure effects, principally conformational planarization. The additional contribution from interchain pi-electron interactions accounts for the larger redshift of thin films.