Abstract
AbstractRed‐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.
Highlights
A significant number of heterocyclic analogues of nanographenes are known to date,[1,2] but the overwhelming majority lack electron-withdrawing and/or electron-donating groups and remain unpolarized
We provide the first examples of X-shaped, highly polarized, p-expanded diketopyrrolopyrroles synthesized by the N-arylation of DPPs followed by an intramolecular direct arylation of the aromatic rings that are present in these building blocks
The construction of p-expanded DPPs requires the installation of two aryl substituents possessing bromine atoms adjacent to the linking positions on the DPP nitrogen atoms
Summary
A significant number of heterocyclic analogues of nanographenes are known to date,[1,2] but the overwhelming majority lack electron-withdrawing and/or electron-donating groups and remain unpolarized. This can be attributed to significant difficulties originating from the lack of compatibility between the required functional groups and the synthetic methods used. To achieve such a goal, rather than decorating large psystems with electron-withdrawing and electron-donating substituents, one may envision the use of highly polarized heterocyclic scaffolds. We provide the first examples of X-shaped, highly polarized, p-expanded diketopyrrolopyrroles synthesized by the N-arylation of DPPs followed by an intramolecular direct arylation of the aromatic rings that are present in these building blocks
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