Dibenzofuran[a]-Fused BODIPYs: Synthesis, Photophysical Properties, and N2O2-Boron-Chelation Towards NIR Materials for Application in Organic Photodetectors

Abstract

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 λ_max 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 (Φ=5.1 %) and 470 nm (Φ=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 μW cm⁻²) produced a photocurrent of 6.05×10⁻⁷ A cm⁻² at a bias potential of 0.1 V.