High Solid-State Near Infrared Emissive Organic Fluorophores from Thiadiazole[3,4-c]Pyridine Derivatives for Efficient Simple Solution-Processed Nondoped Near Infrared OLEDs

Many efforts have been dedicated to developing near infrared (NIR) fluorescent emitters with strong emission especially in the range of 700-1000 nm due to their potential applications in biomedical and optoelectronic fields. However, high solid state NIR emission fluorophores are still rare for applications. Herein, two efficient donor-pi-acceptor type NIR emitters, C3HTP and C4HTP, are designed and synthesized by end-capping two isomeric bis(n-hexylthienyl)thiadiazole[3,4-c]pyridines as pi-acceptor with structural bulky, electron rich tercarbazole moiety. They exhibit excellent solid state NIR emission with an emission peak at 725 nm, especially C3HTP, reaching a record high photoluminescence quantum yield (phi(PL)) of 34% for NIR organic fluorescent materials. By taking advantage of their phi(PL) values in the film state (phi(PL) = 10-34%), suitable energy levels (highest occupied molecular orbital (HOMO) level approximate to -5.3 eV), high hole mobility (5.49 x 10(-8) cm(2) V-1 s(-1)) as well as good amorphous film forming ability by solution casting, they are used to fabricate a nondoped emissive layer (EML) in simple double-layer solution processed NIR electroluminescent (EL) devices. The device containing C3HTP as the EML shows a NIR emission peaking at 726 nm and excellent EL performance with a high external quantum efficiency of 1.51%, which is the best solution processed nondoped NIR organic light-emitting diodes reported to date. Importantly, this represents an advance in near infrared organic fluorescent materials and EL devices that meet the requirements of many applications.