Spectroscopic study of Mq3 (M=Al, Ga, In, q=8-hydroxyquinolinate) at high pressure

A high-pressure spectroscopic investigation of OLED materials with generic formula Mq3 (M=Al, Ga, In, q=8-hydroxyquinolinate) has been carried out. The meridional isomer of Alq3, Gaq3, Inq3 and facial isomer of Alq3 have been produced and their corresponding photoluminescence emission energy has been studied as a function of the cation, pressure, excitation wavelength and isomer. A redshift in the order of 0.3 eV takes place for the pure-meridional isomer compounds in the 0–8 GPa range. We have detected the occurrence of pressure-induced phase transitions presenting hysteresis to ambient conditions. In the case of the facial isomer, luminescence does not significantly redshift until very high pressure. We interpret these features in terms of the enhancement of the intermolecular interaction.