BODIPY Dimers with a Fused and Coplanar Structure: Photophysical Comparison, Low Threshold for Amplified Spontaneous Emission, and Deep-Red Bio-Imaging/Photodynamic Therapy Application

Abstract

Boron dipyrromethene (BODIPY)-derived dyes are generally superior emitters, but their absorption and emission fail to match the bio-active optical window (650–900 nm). In this work, we explored four bisBODIPY dyes (PB1–PB4) with easy-to-go synthesis, good solubility, high photostability, and high emission quantum yield in the deep-red region. Methyl and ethyl groups were introduced in these BODIPY dyes to improve their solubility. PB4 having a fused coplanar plane was synthesized and compared to PB1–PB3 having a non-fused structure. Their geometric structure was confirmed by single-crystal analysis, and their electronic structure, along with one-photon and two-photon absorptions, was analyzed by time-dependent functional theory calculation. Their absorption/emission spectra, emission quantum yields, and lifetimes were compared. It was found that the fused coplanar structure successfully red shifted PB4 absorption/emission to the deep-red region (698/720 nm), with a quantum yield of 0.58. PB4 showed an amplified spontaneous emission effect with an output efficiency of 6.0% at a pumping power of 3000 μJ. An improved photodynamic therapy (PDT) performance was observed from PB4 via in vitro and in vivo experiments. The practical PDT performance was evaluated by cell availability. Upon a 980 nm laser radiation of 5 min, the cell viability was decreased to ∼15%.

Recent advances in highly-efficient near infrared OLED emitters

“…The luminophores used for such applications include fluorescent materials like boron-dipyrromethenes (BODIPYs), 18–20 metalorganic phosphorescent materials, TADF 21 and metal-free room temperature phosphorescence (RTP) 22,23 amongst others as well as inorganic nanoparticles, 24,25 H- and J-dimers of organic materials and aggregates. 26–28 Red emitting fluorophores are often planar molecules with extended π conjugation, such as rylenes, porphyrins and electron donor–acceptor (D–A) systems. Organic fluorophores can have broad PL spectra (large full width at half maximum, FWHM values), however there are classes of dyes like BODIPYs and rylenes that can afford high colour purity (small FWHM) as well as good PLQY values.…”