Photophysical

electrochemical and optoelectronic properties of a conjugated polymer

poly (p-phenylene benzobisoxazole)(PBO) were investigated.Due to its delocalized π electrons in chemical structure

thematerial is low in solubility

excellent in thermo-oxidative stabilities and mechanical properties; it becomes increasingly important inmany applications.This work focused on the photophysicalproperties

in particular the luminescence property of PBO and its preliminary lightemitting device fabrication.The properties of thematerialwere investigated using absorption

and luminescence spectrometries

cyclic voltammetry.Photoluminescence from PBO solutionwere in the range of 430~500 nm.Concentration dependencewas observed.Photoluminescence of the film peaked at 500 nm.Itwas indicated that the emission shift from solutions is due to the intermolecular interaction.Through electro-chemical analysis of the polymer the highestlevel occupied molecular orbital (HOMO) is about

E

HOMO

=5.69eV

through spectral analysis the lowestunoccupiedmolecularorbital energy (LUMO) is about

E

LUMO

=2.99eV.Singlelayer and double-layer lightemitting deviceswere prepared

which have structures as follows: (a)ITO/PBO(60 nm)/Al for the single-layerdevice

and (b)ITO/CuPc(25 nm)/PBO(60 nm)/Al double-layer device.Their currentvoltage characteristicswere analyzed and compared.Although CuPc absorbed in visible

itshowed a transmittedwindow around green spectral range.This allows the light from the device through as it emitted in green around 520 nm.Brightness and stabilityweremuch improved in double-layerdevices.However a voltage-dependentcolour changewas observed for the doublelayerdevice.The electroluminescence intensity is increased as the voltage increase

which reaches amaximum at 21V.The red shift isobserved in the emission spectra as the driving voltage increased.It is predicted that thismay be related to excitation state of PBO at the different field strength

which requires further investigation in the future.