Green, solvent-free synthesis of divinylbenzo[c][1,2,5]thiadiazole emitters via the hand-grinding Horner–Wadsworth–Emmons reaction for high-performance OLEDs

Abstract

Divinylbenzo[c][1,2,5]thiadiazole (DBTDz)-based compounds were investigated as electroluminescent emitters for organic light-emitting diodes (OLEDs), covering emission wavelengths from yellow to near-infrared (NIR). In our recent report, we have described a new eco-friendly, solvent-free synthesis strategy for DBTDz-based fluorescent emitters, carried out by hand grinding the reactants using a mortar and pestle in the presence of potassium tert-butoxide, yielding 24 carbonyl derivatives in excellent isolated yields within one minute. Among all, three derivatives—DBTDz, DBTDz-F, and DBTDz-OMe—were shown to have excellent photoluminescence quantum yields (PLQYs) of 70.5%, 86.6%, and 78.4%, fluorescence lifetimes of 6.1, 5.4, and 4.3 ns and emission maxima at 533, 551, and 620 nm, in a toluene solution, respectively. These three derivatives were studied in different host environments: CBP for yellow-emitting DBTDz and DBTDz-F and a TCTA : CN-T2T (1 : 1) exciplex system for red-emitting DBTDz-OMe. Photophysical and electroluminescence analyses revealed that all emitters exhibited prompt fluorescence with high quantum efficiency and well-confined exciton formation. Devices using DBTDz-F achieved a maximum luminance of 59 152 cd m⁻² and an external quantum efficiency (EQE) of 5.0%, while DBTDz-OMe-based devices showed tunable electroluminescence peaks from 664 to 712 nm depending on the doping concentration, with a peak EQE of 6.1% at 2 wt%. These results demonstrate that DBTDz derivatives, particularly DBTDz-OMe, offer promising potential for wavelength-tunable OLEDs targeting both visible and NIR applications.