Low-molar-mass electroluminescent

The molecular structures 38-43 shown in Table 5.9 are typical of red, low-molar-mass electroluminescent materials. The number of efficient low-molar-mass electroluminescent materials emitting in the red is relatively limited. The europium complexes (38 and 39) " exhibit narrow emission spectra in the red part of the visible spectrum. The first europium complexes synthesised, such as compound 38, were not stable enough to be deposited by physical vapour... 

An alternative approach is to dissolve an efficient electroluminescent chro-mophore in an inert polymer host in a guest-host system or polymer blend. Unfortunately, phase separation and demixing often limits the amount of low-molar-mass electroluminescent chromophores that can be dissolved in polymer hosts. Therefore, the relative brightness is lower for such guest-host systems. This problem can be overcome by fixing the chromophore chemically to the polymer itself as a pendent group on a side-chain polymer separated by spacer units. Bulk phase separation is then impossible, although microphase separation may still take place. This is illustrated by the structures collated in Table 6.10 for some typical side-chain polymers 53-55. ... 

The configuration and construction of monolayer and multilayer OLEDs have undergone substantial changes and modifications since these first reports of organic electroluminescence from low-molar-mass materials. Several types of OLEDs using small organic and organometallic molecules are described schematically below. 

Figure 5.1 Schematic representation of a monolayer OLED using low-molar-mass materials incorporating an electroluminescent material between a transparent anode and a cathode.

Green Electroluminescent, Low-Molar-Mass Organic Materials... 

---