Organic near-infrared (NIR) lumiphores have been targeted for biological and technological applications; however, these dyes exhibit exponentially decreasing quantum yields with decreasing energy gaps. The accepted model of this phenomenon invokes C–H stretching modes as the dominant route of non-radiative energy dissipation. Reducing the number of these modes is a popular strategy for the design of bright NIR lumiphores, but quantitative experimental validation of this strategy is lacking. Here, we evaluate the role of C–H modes in non-radiative relaxation through isotopic labeling of a NIR-emitting complex. Measurements comparing relaxation between protonated and perdeuterated complexes indicate that C–H modes do not contribute significantly to non-radiative relaxation. We instead propose that skeletal modes may play a larger role and suggest that minimizing scaffold size is a promising route for bright NIR lumiphores. We demonstrate the promise of such strategies through the development of the reddest organic-based laser dye yet reported.

有机近红外 (NIR) 荧光体已针对生物和技术应用；然而，随着能隙的减小，这些染料的量子产率呈指数下降。这种现象的公认模型将 C-H 拉伸模式作为非辐射能量耗散的主要途径。减少这些模式的数量是明亮近红外荧光体设计的流行策略，但缺乏对该策略的定量实验验证。在这里，我们通过近红外发射复合物的同位素标记来评估 C-H 模式在非辐射弛豫中的作用。比较质子化和全氘化配合物之间的弛豫的测量结果表明，C-H 模式对非辐射弛豫没有显着贡献。相反，我们认为骨架模式可能发挥更大的作用，并建议最小化支架尺寸是明亮近红外荧光体的一条有前途的途径。我们通过开发迄今为止报道的最红的有机基激光染料来证明这种策略的前景。