the incorporation of oxadiazole together with fluorene and a flexible diarylsilyl group into the same polymer chain, minimizes the trade-off between the processability and high-performance properties of wholly aromatic polyoxadiazoles.
Polyoxadiazoles I and copolyoxadiazoles II containing fluorene moieties were synthesized as was described in Ref.
The light-emitting ability of polymers I containing oxadiazole rings and of polymers II containing oxadiazole and fluorene chromophores was assessed on the basis of PL spectra recorded for polymer films cast from NMP solutions (polymers I) and THF solutions (copolymers II), after irradiation with UV light.
By exciting at their maxima absorption wavelength (~330 nm for la and Ha and ~300 nm for Ib,c and IIb,c), all the polymers displayed blue-light emission with strong maxima of PL centered between 420 and 458 nm, which are determined by the presence of both oxadiazole and fluorene chromophores.
Two series of polymers, one containing oxadiazole rings, and another one containing both oxadiazole and fluorene units, were studied with regard to their optical and electrochemical properties.
In fluorene-benzothiadiazole compound, the equilibrium geometry structure arises from a compromise between the electronic conjugation among phenylene rings and steric repulsions occurring between nitrogen atom of benzo-thiadiazole unit and hydrogen atoms of fluorene units.
Another way to tune and ameliorate the photophysical properties of the PFBT is to substitute the carbon of fluorene bridge with nitrogen element (Scheme lb).
Because of the electron-donating ability of carbazole unit, which is slightly stronger than that of fluorene group, the absorption maximum ([Z.
Energetically, in comparing [pi]-spacer copolymer to PFBT compound, the increasing [pi]-conjugated length, between the BT units and the fluorene groups, makes the energies of HOMO increase and the energies of LUMO decrease.