Polarised Light Emission from OLEDs

The macroscopic alignment of polymer chains was also achieved by depositing soluble poly(p-phenylenes), such as 37 or poly(3-thiophenes) such as 26, from solution by the Langmuir-Blodgett technique. However, low polarisation ratios ( u/ x) were found for electroluminescence (3 1). 

Low polarisation ratios ( 2 1) for absorption had also been found for amorphous PPV (1) deposited from solution by spin-coating on rubbed poly(tetrafluoroethylene) [PTFE]. It is evident that this could be improved on by making use of the high order parameter and self-organising properties of the nematic phase of liquid crystalline electroluminescent polymers such as those (16, 28 and 78-82) shown in Table 6.16. - 2 ° This was then found subsequently to be the case using thermotropic liquid crystalline polyfluorenes, such as 28 and 80 shown in Table 6.6 and segmented PPV derivatives, such as 81. The nematic phase exhibits the lowest viscosity of 

The order must then be frozen in before crystallisation occurs, since this would result in the formation of grain boundaries and a reduction in transport or emission efficiency. Device breakdown is also a possibility. The most efficient way to fix the liquid crystalline order is the formation of anisotropic networks by the polymerisation of reactive mesogens in the liquid crystalline state.Anisotropic polymer networks formed from the thermal or photoinitiated polymerisation of polymerisable, so-called photoreactive, liquid crystalline monomers have been used in a wide variety of electrooptic applications, see Chapter This is a more attractive approach than cross-linking 

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