Synthesis and applications of luminescent metal complexes

Abstract

A set of new stable salen aluminum luminophores, $[salen(^tBu)_4 Al(OPh(X))]$ was developed for hole-blocking materials. All the complexes are thermally stable and their HOMO-LUMO energy gaps, estimated as 2.9 eV, were enough to apply for OLEDs. Actually, the OLEDs employing salen aluminum complexes produced stable green EL emission of $Ir(ppy)_3$ irrespective of changing current density and showed higher brightness and device efficiency than the BAlq-based device. A series of salen-aluminum complexes, $[(R^5)_2 -salen(3- ^tBu)_2 Al(OC_6H_4 -p-C_6H_5)]$ and $[5,5``-(NMe_3)_2 -salen(3- ^tBu)_2 Al(OC_6H_4 -p-C_6H_5)][OTf]_2$ was prepared to achieve full emission color tuning in the visible region. All the complexes are air-stable in both the solid and solution states and exhibit high thermal stability with thermal decomposition temperatures of $313-338^\circ C$. DSC analyses show that the complexes are able to form amorphous glasses with glass transition temperatures of $95-132^\circ C$. UV-vis absorption spectra of the complexes exhibit major absorption bands at 338-413 nm assignable to salen-centered $\pi-\pi^*$ transitions. In particular, the emission spectra of salen-aluminum complexes display the emission maxima over the entire visible region ranging from 438 nm to 599 nm. Inspection of the HOMO and LUMO energy levels determined experimentally indicates that the HOMO levels systematically increase, while the LUMO levels remain almost unchanged. Density-functional theory calculations are in good agreement with the experimental data. The OLED performance of the salen-Al complex 2 as fluorescent emitting materials showed sky-blue emission at 478 nm and brightness of $1,800 cdm^{-2}$ at $100 mAcm^{-2}$. Salen-Al complexes can serve as color tunable fluorescence emitter for OLED. Various dinulear salen aluminum complexes as host materials, $[Salen(^tBu)_n AlOPh]_2 C(CX_3)_2$ were developed for spin-coating OLEDs. All the complexes exhibit high thermal stabi...