J‑Aggregate Behavior of Poly[(9,9- dioctyluorenyl-2,7-diyl)- alt -co-(bithiophene)] (F8T2) in Crystal and Liquid CrystalPhases

Poly [(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(bithiophene)] (F8T2) in thermally annealed films exhibits red-shifted absorption spectra, which shows the typical feature of the J-aggregate and is confirmed by computational simulations. By controlling the annealing temperature, the aggregate behavior is explored in detail. It is found that the J-aggregate is formed only when the material is annealed at crystallization and liquid crystal temperatures. The microstructure and morphology of the aggregates show that the J-aggregates have tighter chain packing and a larger ordered domain. This work first demonstrates the Jaggregate behavior of the F8T2 material and establishes the relationship between optical spectra and the packing structure of F8T2.