Wu Chunxiao, Lu Chen, Yu Shilong, Zhang Minzhe, Zhang Houyu, Zhang Ming, Li Feng
State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Qianjin Avenue 2699, Changchun, 130012, P. R. China.
Angew Chem Int Ed Engl. 2024 Dec 20;63(52):e202412483. doi: 10.1002/anie.202412483. Epub 2024 Oct 24.
Purely organic molecules exhibiting near-infrared (NIR) emission possess considerable potential for applications in both biological and optoelectronic technological domains, owing to their inherent advantages such as cost-effectiveness, biocompatibility, and facile chemical modifiability. However, the repertoire of such molecules with emission peaks exceeding 750 nm and concurrently demonstrating high photoluminescence quantum efficiency (PLQE) remains relatively scarce due to the energy gap law. Herein, we report two open-shell NIR radical emitters, denoted as DMNA-Cz-BTM and DMNA-PyID-BTM, achieved through the strategic integration of a donor group (DMNA) onto the Cz-BTM and PyID-BTM frameworks, respectively. We found that the donor-acceptor molecular structure allows the two designed radical emitters to exhibit a charge-transfer excited state and spatially separated electron and hole levels with non-bonding characteristics. Thus, the high-frequency vibrations are effectively suppressed. Besides, the reduction of low-frequency vibrations is observed. Collectively, the non-radiative decay channel is significantly suppressed, leading to exceptional NIR PLQE values. Specifically, DMNA-Cz-BTM manifests an emission peak at 758 nm alongside a PLQE of 55 %, whereas DMNA-PyID-BTM exhibits an emission peak at 778 nm with a PLQE of 66 %. Notably, these represent the pinnacle of PLQE among metal-free organic NIR emitters with emission peaks surpassing 750 nm.
具有近红外（NIR）发射特性的纯有机分子在生物和光电子技术领域均具有巨大的应用潜力，这得益于其具有成本效益、生物相容性和易于化学修饰等固有优势。然而，由于能隙定律，发射峰超过750 nm且同时具有高光致发光量子效率（PLQE）的此类分子的种类仍然相对较少。在此，我们报告了两种开壳型近红外自由基发射体，分别记为DMNA-Cz-BTM和DMNA-PyID-BTM，它们是通过将供体基团（DMNA）分别战略性地整合到Cz-BTM和PyID-BTM框架上而实现的。我们发现，供体-受体分子结构使这两种设计的自由基发射体表现出电荷转移激发态以及具有非键合特征的空间分离的电子和空穴能级。因此，高频振动得到有效抑制。此外，还观察到低频振动的减少。总体而言，非辐射衰变通道被显著抑制，从而导致优异的近红外PLQE值。具体而言，DMNA-Cz-BTM在758 nm处表现出发射峰，PLQE为55%，而DMNA-PyID-BTM在778 nm处表现出发射峰，PLQE为66%。值得注意的是，这些代表了发射峰超过750 nm的无金属有机近红外发射体中PLQE的最高水平。
