Thermally Activated Delayed Fluorescence of Aggregates Induced by Strong π–π Interactions and Reversible Dual-Responsive Luminescence Switching

Abstract

A reversible dual-responsive luminescent material was introduced by our group to show the simultaneous color and lifetime switching in response to external stimuli. Pristine crystalline powder of (E)-2-(benzo[d]thiazol-2-yl)-3-(pyren-1-yl)acrylonitrile (Py-BZTCN) shows the ordered π-π stacking with only near-monomer-normal orange-yellow fluorescence, but it exhibits red emission with thermally activated delayed fluorescence (TADF) after grinding, which can be reversibly recovered by heating or fuming treatment. Grinding disturbs the ordered π-π stacking of pristine powder, leading to the formation of small aggregates with compressed distance and increased overlap of π-π stacking between adjacent molecules. The cause of switching was verified by single-crystal X-ray diffraction experiments of two corresponding crystals. This strong π-π interaction effectively promotes the excited-state energy splitting and substantially decreases the singlet-triplet energy gap (ΔE ST ) of aggregates, resulting in the red TADF emission of aggregates through reverse intersystem crossing. This finding proposes a new route to realizing the TADF emission of aggregates through strong intermolecular interactions based on non-TADF monomer, thereby enabling a novel high-contrast dualresponsive luminescence switching.

Robust formation of discrete non-covalent pyrene dimers in an amorphous film by strong π–π interaction

“…It is known that the interplanar distance and overlap are two important factors to evaluate the intermolecular π–π interaction, and small distance and large overlap are conducive to strengthening the π–π interaction. 5 a ,10 In previous studies, there was hardly one Py-based dimer with such a large overlap and such a close interplanar distance simultaneously, which means that the stronger intermolecular π–π interaction may exist in the Py-based π–π dimer in this study. 7 d…”

Switching Monomer‐to‐Excimer Fluorescence by Noncovalent Interaction Competition Strategy

“…And it showed green fluorescence with a λ max at 500 nm (Figure S8, Supporting Information). [ 27 ] The second crystal (Crystal‐A) was obtained via solvent volatilization from concentrated chloroform (CHCl 3 ) or deuterated chloroform (CDCl 3 ) solution and then could turn to the third crystal (Crystal‐B) once Crystal‐A was taken out of the solution. The transformation from Crystal‐A to Crystal‐B was accompanied by a morphological change from transparent to cloudy as well as an emission color change from yellow to bluish‐green (Figure S9, Supporting Information).…”

Pressure-shortened delayed fluorescence lifetime of solid-state thermally activated delayed fluorescent 4CzIPN: the structure evolution

“…13 Recently, Wang and co-workers reported a novel MCL-active TADF material based on the change of packing arrangements. 14 However, despite these advancements, research on efficient TADF with pressure-induced emission enhancement (PIEE) and multicolor MCL materials remains in its infancy due to the lack of systematic molecular design.…”