Design and Synthesis of Piezochromic Materials Based on Push–Pull Chromophores: A Mechanistic Perspective

Abstract

Computational analysis predicts that intramolecular charge transfer (ICT) exists in anthraquinone imide (AQI) derivatives with electron-donating substituents at the 6-position, such as 4-methoxylphenyl, 4-N,N-dimethylaminophenyl, and thiophene. However, for those with electron-withdrawing ones, no clear ICT interaction could be observed. We predicted, on the basis of the simulation results, that AQI derivatives with electron-donating substituents would be piezochromic. To verify this hypothesis, the corresponding AQI derivatives with various substituents were synthesized. Absorption spectra recorded with a diffuse reflectance method on powders revealed that 4-methoxylphenyl-, 4-N,N-dimethylaminophenyl-, and thiophene-substituted AQI exhibited piezochromism, but not 4-nitrophenyl-substituted AQI, which is in good agreement with the simulation results. Interestingly, redshifts of both the lower and higher energy absorption bands were observed along with redshifts of the emission spectra. However, XRD patterns before and after being pressed presented no significant changes, which was different from known piezochromic molecules described in the literature. An unprecedented mechanism in which enhanced ICT from better conjugation between the donor and acceptor segments induced by the decrease of θ under pressure could be responsible for the piezochromism of aryl-substituted AQIs is proposed.

Mechanosensitive Membrane Probes

“…Mechanophore 16 arguably comesc losest to ap lanarizable push-pull probe ( Figure 6). [30] An imide acceptor and amethoxy donor are separated by at wist that partially deconjugates the extended aromatic system.M echanosensitivity,a lthough weak, is demonstrated with ar ed shift of Dl abs =+10 nm to l abs = 440 nm under pressure. Red-shifted absorption could be consistent with the expected planarization of the push-pull chromophore in the ground state.…”

Oligothiophene Amphiphiles as Planarizable and Polarizable Fluorescent Membrane Probes

“…[6][7][8] The deplanarization of push-pull fluorophores in the excited state received much attention in the context of molecular rotors. [10] The planarization of oligothiophenes and related chromophores [11,12] without push-pull substituents has been studied extensively because of their intrinsic solvatochromism and thermochromism, and because of their promise in molecular electronics, photonics, and photovoltaics and as sensing devices. [9] The planarization of push-pull fluorophores in the ground state has received much less attention, and the few existing examples focus on piezochromism of aggregates rather than on isolated molecular probes in hosts, such as lipid bilayer membranes.…”

“…[9] The planarization of push-pull fluorophores in the ground state has received much less attention, and the few existing examples focus on piezochromism of aggregates rather than on isolated molecular probes in hosts, such as lipid bilayer membranes. [10] The planarization of oligothiophenes and related chromophores [11,12] without push-pull substituents has been studied extensively because of their intrinsic solvatochromism and thermochromism, and because of their promise in molecular electronics, photonics, and photovoltaics and as sensing devices. The responsiveness of oligothiophenes to the envi-ronment originates from the small energy cost for rotation around the a,a'-single bonds between two thiophene rings.…”

“…Although the complexity of the system suggests that alternative explanations should not be fully excluded at this stage, these initial results on a new topic are in perfect agreement with expectations, provide clear guidelines for the continuation, and promise attractive applications. Specifically, we now try to first maximize sensitivity and contrast with increasingly twisted, polarized, shortened, or elongated oligothiophenes, [19] and then to explore the detectability of membrane tension [20] or heterogeneity ("rafts") [3] together with applications toward live cells (neurons, etc) [3,5] and functional materials (artificial photosystems, [21] piezochromism, [10] NLO, etc).…”

The Synergistic Effect between Triphenylpyrrole Isomers as Donors, Linking Groups, and Acceptors on the Fluorescence Properties of D–π–A Compounds in the Solid State

“…The resultsclearly demonstrated that the piezochromic properties should be attributed to the change in intermolecular arrangementp attern from the crystalline state to the amorphous state. [40][41][42][43][44][45] Comparing the spectra before and after being ground, the absorbance wavelength and emission wavelength of the compounds in the amorphous state are longert han those in the crystalline state, which further proved the analysis ( Figure S11int he SupportingI nformation).…”