Blue-shifted aggregation-induced emission enhancement (AIE) from fluorinated Sn hydroxyquinoline derivative complexes for organic light-emitting diode applications

Abstract

Aggregation-induced emission enhancement (AIE), emission enhancement upon aggregate formation arising from the restriction of intramolecular rotation and vibration, has been observed in many organic materials. This AIE property is advantageous over the more commonly observed aggregation caused quenching (ACQ) for organic light-emitting diodes (OLEDs), which rely on solid-state materials in the emitting layer. ACQ phenomenon has been a critical issue in limiting the efficiency of OLEDs. Herein, we present the synthesis of Sn(IV) complexes from 8-hydroxyquinoline (q) and 5,7-dimethyl-8-quinolinol (me2q) and examine structural, optical, thermal and AIE properties for OLED applications. For Snq2X2 and Sn(me2q)2X2 (X=F, Cl), a unique halide exchange from Cl to F was achieved through fluoride ion, a degradation product of hexafluorophosphate, complexing the Sn center and replacing Cl.  The fluorinated Sn complex produces significantly improved thermal stability and quantum efficiency for Snq2X2. Single crystallographic data and cyclic voltammetry reveal such phenomena are attributed to stronger σ bonding interaction between Sn and F, however both F and Cl versions of Sn(me2q)2X2 show identical relative quantum yields (ΦPL, solution=0.5%). Interestingly, Snq2F2 shows significant AIE properties (ΦPL, solid=17%) while Snq2Cl2 does not, but both the Cl and F versions of Sn(me2q)2X2 display moderate AIE properties (ΦPL, solid=4% and 6% for Sn(me2q)2F2 and Sn(me2q)2Cl2, respectively).

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