One-Pot Synthesis and Excited-State Dynamics of Null Exciton-Coupled Diketopyrrolopyrroles Oligo-Grids.

Exciton coupling in molecular aggregates plays a vital role in impacting and fine-tuning optoelectronic materials and their efficiencies in devices. A versatile platform to decipher aggregation-property relationships is built around multichromophoric architectures. Here, we designed a series of cyclic diketopyrrolopyrroles (DPPs) oligomers featuring nanoscale gridarene structures and rigid bifluorenyl spacers. Dimers and trimers, that is, [2]Grid and [3]Grid, were synthesized via one-pot Friedel-Crafts reactions. The two of them, which are cyclic rigid nanoarchitectures of rather different sizes, were characterized by means of steady-state and time-resolved absorption and fluorescence spectroscopies. This was not only meant to systematically investigate exciton couplings among DPPs but also to determine their excited-state dynamics. [2]Grid and [3]Grid exhibited monomer-like spectroscopic signatures in the steady-state measurements, from which we derive null exciton couplings. Moreover, in apolar solvent, high fluorescence quantum yields and excited-state dynamics that resembled DPP monomer were gathered. In polar solvent, the localized singlet excited state on a single DPP dissociates into the adjacent null coupling DPPs with charge transfer characteristics. This pathway facilitates the evolution of charge-separated states. [2]Grid, for example, reveals an efficient population of the symmetry-broken charge-separated state (SB-CS) in benzonitrile. Notable is the fact that the SB-CS of [2]Grid is, on one hand, in an equilibrium with the singlet excited state and promotes, on the other hand, the formation of the triplet excited state with a yield of 32% via charge recombination. This article is protected by copyright. All rights reserved.