Remarkable Turn‐On and Color‐Tuned Piezochromic Luminescence: Mechanically Switching Intramolecular Charge Transfer in Molecular Crystals

Abstract

4005wileyonlinelibrary.com in a low contrast ratio in the luminescence recording.High-contrast luminescence recording requires not only the obvious two-color luminescence switching, but also the dramatic switching in the luminescence intensity which is diffi cult to realize for the traditional piezochromic luminescent materials. [ 4 ] Recently, a few piezochromic materials with on-off or off-on luminescence property have been reported. Pei and co-workers [ 5 ] reported a turn-on luminescence of cocrystallized complex of 2,5-di( E )-distyrylfuran and N -alkyl-substituted maleimides by breaking the donoracceptor (D-A) interaction after applying mechanical force. Park and co-workers [ 4b , 6 ] found the mechanically controlled photoinduced electron transfer in molecular assemblies of dicyanodistyrylbenzene derivative with the obvious off-on luminescence, and shear-induced luminescence onoff switching in stilbenic π-dimer crystals by reversible [2 + 2] cycloaddition. Tang and co-workers [ 7 ] and Wang and co-workers [ 8 ] reported some crystallization-induced emission enhancement (CIEE) materials with on-off emission under grinding, respectively. In addition, Tang [ 9 ] reported the mechanical force induced off-on emission of the defect-sensitive crystals based on diaminomaleonitrile-functionalized Schiffbase. Almost all the above researches focused on the luminescence change under the mechanical grinding. However, the magnitude of the grinding force cannot be precisely controlled and the direction of the grinding force is anisotropic, which is diffi cult to investigate the mechanism of the piezochromic luminescence by mechanical grinding. Instead, the research of piezochromic luminescence under hydrostatic pressure is a more effective and controllable method to explore the piezochromic mechanism. Our group [ 10 ] and Yamaguchi group [ 11 ] have reported piezochromic luminescence of 9,10-bis(( E )-2-(pyrid-2-yl)vinyl)anthracene and tetrathiazolylthiophene, respectively, which both showed gradually redshifted wavelength and decreased intensity of luminescence due to the enhanced π-π interaction under the hydrostatic pressure.Herein, a structurally well-defi ned donor-acceptor (D-A) molecule, AD-TPE ( Figure 1 a), incorporating a twisted TPE unit as an electron donor, and a rigid AD unit as an electron acceptor have been readily synthesized with high yield according to Scheme S1 (Supporting Information) via the C-N couplingThe molecular crystals of acridonyl-tetraphenylethene (AD-TPE) exhibit an intriguing turn-on and color-tuned luminescence in response to mechanical grinding and hydrostatic compression. On the basis of in-depth experimental and computational studies, it is hypothesized that the origin of the piezochromic behavior from the D-phase to the B-phase is the change of the intramolecular geometrical conformation, especially for the torsion angle between the TPE and AD moiety. The different molecular conformation in the two distinctive solid phases causes the substantial switching of the intramolecular cha...

Small Changes With Big Consequences: Swapping Two Atoms In Side Chains Changes Phenylene‐Ethynylene Packing And Fluorescence

“…This shift reverses with thermal annealing, and is consistent over multiple cycles (Figures S4–S6, Supporting Information). In addition, fluorescence of the metastable state achieved upon shearing evolves over time at room temperature: initial grinding of a film of 2 , 4 , 6‐OMe yields bright green fluorescence with a ≈1.7× increase in total emission intensity and 36 nm shift, which we attribute to shear‐induced planarization and/or aggregation of these twisted molecules . Over the course of minutes, this emission dims and shifts to 467 nm, after which point additional heating below the melting point fully restores the original emission.…”

Effects of N‐Substitution on the Property of Acridone

“…Although there are some reports on the aromatic groups connecting to the amino group of acridone, the study on their physicochemical properties is still rare, probably due to the consideration of the reduced conjugation by the nitrogen atom. With some peculiar aromatic groups, such as biphenyl carbazole, tetraphenylethylene, the obtained compounds showed interesting electroluminescence and piezochromic luminescence. Thus the N ‐substitution of acridone is also feasible to attain the organic functional materials, in particular, when there are competitions of charge transfers in acridone and between the nitrogen atom of acridone and the substituent.…”

Piezochromic Luminescence of Donor–Acceptor Cocrystals: Distinct Responses to Anisotropic Grinding and Isotropic Compression

“…Theh igh-pressure experiments were performed by using ad iamond anvil cell (DAC) with silicone oil as ap ressure-transmitting medium. [13] Therefore,t hese observations of CT-R cocrystals under the different mechanical force stimuli suggest that this unique piezochromic behavior may come from the different nature. Besides,t he fluorescence maximum peak was gradually redshifted and its intensity gradually decreased, and eventually to anear infrared emission at 744 nm when the pressure reached at 5.08 GPa.…”