Porous organic materials discovered a little more than a decade ago have developed rapidly because they offer a number of attractive properties as gas storage or separation materials. They can display high porosities but are processable unlike zeolites or covalent organic frameworks. The spatial shape of organic cages represents a promising platform to study phenomena associated with electronic materials. However, studies of photophysical or electronic properties using organic cages are rare. Previously, we reported a synthesis of a chiral covalent organic cage with three built-in redox-active naphthalene-1,4:5,8-bis(dicarboximide) units by dynamic imine chemistry. We found that intracage photoinduced charge separation provided a long-lived charge separated state and that electrons could migrate between individual redox units demonstrating the potential of organic cages as interesting organic electronic materials.<br/><br/>Here, we present a new cage with three perylene-3,4,9,10-bis(dicarboximide) (PDI) units that displays a delayed fluorescence in a solution unlike a monomeric compound with a single PDI unit. The measured quantum yields and the fluorescence lifetimes suggest a formation of a non-emissive state on a nanosecond time-scale that is in a dynamic equilibrium with the bright monomer-like excited state. The observed interconversion rates and the equilibrium between these states depend on the polarity of the solvent. The spatial arrangement of the PDI units revealed by single-crystal X-ray diffraction and DFT calculations allows only for a weak coupling between the individual PDI units as probed by cyclic voltammetry, and steady-state optical spectroscopies. Our data hint that the new non-emissive state is formed either via a PDI–PDI charge separation or a singlet fission event.

Delayed fluorescence in a chiral perylene-3,4,9,10-bis(dicarboximide) organic cage

ACS Spring Meeting 2021

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