Efficient Near-Infrared (NIR) Organic Light-Emitting Diodes Based on Donor-Acceptor Architecture: An Improved Emissive State from Mixing to Hybridization

Herein, a high-efficiency near-infrared (NIR) material PXZ-3-NZP is designed and sythesized using the concept of hybridized local and charge-transfer (CT) state (HLCT), which is composed of donor (D) and acceptor (A) moieties as well as 10-substituted isomeride PXZ-10-NZP for the purpose of comparison and deep understanding on the essential difference of their excited state properties. As a result, the nondoped electroluminescent (EL) device of PXZ-3-NZP exhibits an excellent NIR emission (lambda(max) = 738 nm) with a maximum external quantum efficiency (eta(EQE)) of 0.82% and a Commission International de L'clairage coordinate of (0.70, 0.29), which is record-setting among NIR fluorescent organic light emitting diodes with similar EL chromaticity. Also, a high (EQE) of 2.03% is achieved in a doped device with a deep red emission at lambda(max) = 676 nm. As a comparison, PXZ-10-NZP shows far inferior performance to those of PXZ-3-NZP in both nondoped and doped devices, due to the instinct CT character of its S-1 excited state. In terms of excited state, HLCT state is exactly superior to mixed state in high-efficiency luminescence, which is a particularly useful strategy to design narrow-bandgap light-emitting materials beyond energy gap law with donor-acceptor architectures.