4. D-π-A molecular fluorescent emitters

A key feature of diodes based on D-π-A materials is the phenomenon of charge-transfer luminescence. Charge transfer in organic semiconductors can be generated electrically (Electrogenerated Charge Transfer or ECT) or photochemically (Photoinduced Charge Transfer or PCT). PCT involves D-π-A molecules in solution, while ECT is a solid-state phenomenon in diodes.

Two important phenomena are the consequence of ECT in an OLED:

• the greater the charge transfer, the greater the emission;

• the greater the charge transfer, the more the emission is bathochromically shifted (towards higher wavelengths).

The stronger the charge transfer, whether generated by ECT or PCT, the more the light emission will be red-shifted, so the OLED will perform better, but will...