NIR‐II Absorbing Monodispersed Oligomers Based on N−B←N Unit

Abstract

Organic molecules with near‐infrared II (NIR II) light absorption are essential for many biological and opto‐electronic applications. Herein, we report monodispersed oligomers as NIR II light absorber using a new molecular design strategy of resonant N−B←N unit, i.e. balanced resonant boron‐nitrogen covalent bond (B−N) and boron‐nitrogen coordination bond (B←N). We synthesize a series of monodispersed oligomers with thiophene‐fused 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (TB), which contains resonant N−B←N unit, as the repeating unit. The TB pentamer exhibits the maximum absorption wavelength of 1169 nm, which is the longest for oligomers reported so far. Organic photodetectors (OPDs) with the TB tetramer as the electron acceptor shows the specific detectivity of 2.98×1011 Jones at 1180 nm under zero bias. This performance is among the best for NIR II OPDs. These results indicate a new kind of NIR II absorbing molecules as excellent opto‐electronic materials.

Boron- and Nitrogen-Embedded Polycyclic Arenes as an Emerging Class of Organic Semiconductors

“…87,88 Recently, Liu and co-workers developed a series of monodisperse thiophene-fused BODIPY oligomers. 89 Theoretical calculations revealed that the resonant N−B ← N units effectively decreased the aromaticity of the aromatic rings and thus improved π delocalization in the oligomers, resulting in intense absorption in the NIR-II region (with an absorption maximum of 1169 nm). Moreover, the potential of thiophenefused BODIPY tetramer as an electron acceptor for NIR-II organic photodetectors (OPDs) was demonstrated, showing a specific detectivity of 2.98 × 10 11 Jones at 1180 nm under zero bias.…”

“…The skeleton of 42 was further utilized as a building block for constructing small-band gap conjugated polymers, which provided new strategies for the design of NIR-absorption materials . This resonant N–B ← N unit has also been observed in BODIPY compounds, which have been applied in various fields because of the excellent stability and interesting photophysical properties. , Recently, Liu and co-workers developed a series of monodisperse thiophene-fused BODIPY oligomers . Theoretical calculations revealed that the resonant N–B ← N units effectively decreased the aromaticity of the aromatic rings and thus improved π delocalization in the oligomers, resulting in intense absorption in the NIR-II region (with an absorption maximum of 1169 nm).…”

Electron-Transporting Properties and Ultrasmall Band Gap of BODIPY-Based Conjugated Polymers: Teach an Old Dog New Tricks

“…We have referred to it as the resonant N–B←N unit in our recent studies . We have found that the resonant N–B←N unit leads to downshifted E LUMO and minimized band gap of the resulting molecules/polymers. , This motivates us to use BODIPY as the building block to design conjugated polymers with an ultrasmall band gap and low-lying E LUMO .…”

“…42 We have found that the resonant N−B←N unit leads to downshifted E LUMO and minimized band gap of the resulting molecules/polymers. 43,44 This motivates us to use BODIPY as the building block to design conjugated polymers with an ultrasmall band gap and low-lying E LUMO . In this work, we report a conjugated copolymer of alternating BODIPY unit and vinylene, P-α-V (see Scheme 1), which shows an ultrasmall band gap and excellent electrontransporting property.…”

Molecular Order Control of Nonfullerene Acceptors Enables Ultralow Dark Current and High Responsivity in Short-Wavelength Infrared Organic Photodetectors

“…Near-infrared (NIR, 780–3000 nm) organic photodetectors (OPDs) have drawn tremendous attentions due to their inherent advantages such as being lightweight, flexible, and compatible with large-area, low-cost fabrication processes, enabling great application potential in sensing, optical communication, medical imaging, artificial intelligence, surveillance, etc. − Generally, the responsivity ( R ) and detectivity ( D *) values at certain wavelength regions are recognized as two key figures of merit for evaluating the performance of OPDs. In the past few years, NIR OPDs possessing comparable R and D * values with silicon photodetectors within the wavelength of 1000 nm have been realized owing to the substantial development of various narrow-bandgap nonfullerene acceptors (NFAs) and high-performance conjugated polymer (CP) donors. − However, NIR OPDs that simultaneously achieve high R and D * in the short-wavelength infrared (SWIR) region (1000–1700 nm) have not been fully developed, causing OPD development to lag far behind their inorganic counterparts, such as indium gallium arsenide (InGaAs) photodetectors. − Therefore, in the realm of materials development, there is an urgent need to explore effective molecular design strategies for creating novel narrow-bandgap NFAs or CPs for OPDs that exhibit outstanding performance in both R and D * in the wavelength region exceeding 1000 nm.…”