Discrete Dimers of Redox-Active and Fluorescent Perylene Diimide-Based Rigid Isosceles Triangles in the Solid State

Abstract

The development of rigid covalent chiroptical organic materials, with multiple, readily available redox states, which exhibit high photoluminescence is of particular importance in relation to both organic electronics and photonics. The chemically stable, thermally robust and redox-active perylene diimide (PDI) fluorophores have received ever-increasing attention owing to their excellent fluorescence quantum yields in solution. Planar PDI derivatives, however, generally suffer from aggregation-caused emission quenching in the solid state. Herein, we report on the design and synthesis of two chiral isosceles triangles wherein one PDI fluorophore and two pyromellitic diimide (PMDI) or naphthalene diimide (NDI) units are arranged in a rigid cyclic triangular geometry. The optical, electronic and magnetic properties of the rigid isosceles triangles are fully characterized by a combination of optical spectroscopies, X-ray diffraction, cyclic voltammetry, and computational modeling techniques. Single-crystal X-ray diffraction analysis shows that both isosceles triangles form discrete, nearly cofacial PDI-PDI π-dimers in the solid state. While the triangles exhibit fluorescence quantum yields of almost unity in solution, the dimers in the solid state exhibit very weak-yet at least an order of magnitude higher-excimer fluorescence yield in comparison with the almost completely quenched fluorescence of a reference PDI. The triangle containing both NDI and PDI subunits shows superior intramolecular energy transfer from the lowest excited singlet state of the NDI to that of the PDI subunit. Cyclic voltammetry suggests that both isosceles triangles exhibit multiple, easily accessible and reversible redox states. Applications beckon in arenas related to molecular optoelectronic devices.

Recent Advances on Stimuli‐Responsive Smart Materials and their Applications

“…In contrast, (–)‐2NDI‐1PDI‐Δ depict five redox processes with six electrons involved in formation of radicals of NDI. Therefore, presence of multiple redox active sites in PMDI, NDI based derivatives provide applications for optoelectronic devices …”

Stereoisomerization during Molecular Packing

“…[ 21,32–35 ] Moreover, strong intermolecular interactions may increase exciton utilization efficiency by hindering molecular motion in the solid state. [ 36–40 ]…”

Perylene diimide-based supramolecular polymer with temperature-sensitive ratiometric fluorescence responsiveness in solution and gels

“…[32][33][34][35] In spite of these advantages, traditional PDI-based supramolecular materials usually suffer from relatively weak fluorescent intensities of redshift emission, low quantum yields, and undesirable ACQ in aggregated states due to the strong intermolecular p-p stacking of the PDI plane. [36][37][38][39] Thus, the optimization of the supramolecular structure to modulate the p-p stacking of PDI is essential to achieve bright emission in the aggregated state, which can be realized by the introduction of various aromatic rings as isolation groups from the sides. 37,38 However, this strategy is often hindered by the complicated synthesis routes, and the obtained dyes generally exhibit a stationary red or deep red emission nature.…”

“…[36][37][38][39] Thus, the optimization of the supramolecular structure to modulate the p-p stacking of PDI is essential to achieve bright emission in the aggregated state, which can be realized by the introduction of various aromatic rings as isolation groups from the sides. 37,38 However, this strategy is often hindered by the complicated synthesis routes, and the obtained dyes generally exhibit a stationary red or deep red emission nature. 40,41 Herein we report our strategy to prepare PDI-based ratiometric fluorescence supramolecular materials that are thermosensitive.…”