Dibenzofuran[a]‐fused BODIPYs: Synthesis, Photophysical Properties, and N 2 O 2 ‐Boron‐Chelation towards NIR Materials for Application in Organic Photodetectors

Highly annulated boron‐dipyrromethenes (BODIPYs) were synthesized with the objective to develop a near‐infrared (NIR)‐absorbing photodetector. Post‐functionalization of the dibenzoBODIPY scaffold enabled it to fuse with the dibenzofuran heterocycle at the a‐bond of the pyrrole unit to give the related dyes 1 and 2, which absorb far‐red light in tetrahydrofuran. Further structural modification by intramolecular B,O‐chelation of 2 yielded the benzo[1,3,2]oxazaborinine‐containing dye 14 having an intense absorption band with a λmax value of 812 nm (ε = 1.3 × 105 M‒1 cm‒1), as rationalized by time‐dependent density functional theory (TD‐DFT)/DFT calculations. Dye 14 exhibited unique emission properties, wherein irradiation at 375 nm led to a dual emission at 822 nm (Ф = 5.1%) and 470 nm (Ф = 7.8%), which could be attributed to the electronic non‐adiabatic coupling due to the large energy difference between the S2 and S1 states, according to the anti‐Kasha rule. Using a resistance‐heating‐type vacuum‐deposition method, the rigid π‐conjugated structure of 14 enabled its application as an NIR photodetector in a single‐component device (indium tin oxide/14/Al). Current‒voltage (J–V) measurements under photoirradiation at 870 nm (120 mW cm‒2) produced a photocurrent of 6.05 × 10‒7 A cm‒2 at a bias potential of 0.1 V.