Red Emitter for OLEDs Based on Bis(8‐hydroxyquinoline) Zinc Complex With Styryl π‐Conjugation and a Cyano Group

ABSTRACT

A zinc complex based on bis(8‐hydroxyquinoline) ligands containing styryl moiety with an electron‐withdrawing cyano substituent (ZnStq_CN) was synthesized and used as a light‐emitting dopant in a poly(9‐vinylcarbazole) (PVK) matrix for an organic light‐emitting diode (OLED) using the spin‐coating method. The cyano group was introduced to enhance intramolecular charge transfer and modulate the electronic structure of the complex. Photophysical studies confirmed enhanced charge transfer character compared with conventional Zn(8‐hydroxyquinolinate) derivatives. OLED devices based on ZnStq_CN:PVK emissive layer exhibited intense red electroluminescence centered at 620 nm with a full width at half maximum of 59 nm. The device achieved a maximum brightness of 1779 cd/m ² , a current efficiency of 0.97 cd/A, a turn‐on voltage of 5.63 V, and a threshold voltage of 7.01 V. Compared with unsubstituted analogs, the cyano‐functionalized complex demonstrated higher luminance, reduced power consumption, improved red color purity, and enhanced operational stability. Theoretical DFT calculations provide insight into the interaction and nature of excited states. These results demonstrate that electron‐withdrawing substitution in Zn‐quinolinate complexes is an effective strategy for tuning the emission characteristics and optimizing the efficiency of red‐emitting OLEDs.