Red‐emissive π‐expanded diketopyrrolopyrroles (DPPs) with fluorescence reaching λ=750 nm can be easily synthesized by a three‐step strategy involving the preparation of diketopyrrolopyrrole followed by N‐arylation and subsequent intramolecular palladium‐catalyzed direct arylation. Comprehensive spectroscopic assays combined with first‐principles calculations corroborated that both N‐arylated and fused DPPs reach a locally excited (S₁) state after excitation, followed by internal conversion to states with solvent and structural relaxation, before eventually undergoing intersystem crossing. Only the structurally relaxed state is fluorescent, with lifetimes in the range of several nanoseconds and tens of picoseconds in nonpolar and polar solvents, respectively. The lifetimes correlate with the fluorescence quantum yields, which range from 6 % to 88 % in nonpolar solvents and from 0.4 % and 3.2 % in polar solvents. A very inefficient (T₁) population is responsible for fluorescence quantum yields as high as 88 % for the fully fused DPP in polar solvents.

中文翻译：

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如何使硝基芳族化合物发光：下一代大型X形，中心对称的二吡咯并吡咯。

荧光达到λ= 750 nm的红色发光π扩展二酮吡咯并吡咯（DPPs）可以通过三步策略轻松合成，包括制备二酮吡咯并吡咯并随后进行N芳基化和随后的分子内钯催化的直接芳基化。综合光谱分析与第一性原理计算相结合，证实了N-芳基化和熔融DPP均达到了局部激发（S ₁激发后的状态，然后内部转化为具有溶剂和结构弛豫的状态，然后最终进行系统间转换。仅结构松弛状态是荧光的，在非极性和极性溶剂中的寿命分别在几纳秒和几十皮秒的范围内。寿命与荧光量子产率相关，在非极性溶剂中，荧光量子产率为6％至88％，在极性溶剂中为0.4％至3.2％。极性溶剂中完全熔融的DPP的荧光量子产率高达88％，效率非常低（T ₁）。