Cation–Anion Interaction‐Directed Molecular Design Strategy for Mechanochromic Luminescence

Abstract

Mechanofl uorochromic materials have great potential for a wide variety of applications such as sensors, memory devices, motion systems, security systems, and so forth. However, only few design principles have been disclosed, which greatly impedes the growth of mechanofl uorochromic dyes. Here, a strategy of molecular design for mechanochromic luminescence is reported, based on the cation-anion interaction-directed switching of molecular stacking. On the basis of this strategy, a series of common N-heteroaromatic onium fl uorophores such as imidazolium, 1,2,4-triazolium, triazolopyridinium, benzoimidazolium, γ -carbolinium, and pyridinium salts have been designed and proved to have striking reversible mechanofl uorochromic behaviors. The simple attachment of a non-fl uorescent imidazolium unit to the pyrene scaffold through a fl exible carbon chain can even trigger the mechanofl uorochromic phenomenon, which gives a consummate interpretation that the cation-anion interaction can be considered as an important general tool to design organic mechanochromic luminescent materials.

Structural Features Guiding the Design of Liquid-Crystalline Elastomeric Fluorescent Force Sensors

“…It is also interesting to stress at this point that mechanochemical reactions can also be performed in polymeric matrixes containing carefully chosen mechanophores with an extremely high spatial precision, permitting 3D nanoprinting and the production of nanodevices and nanosensors for measuring mechanical stress in situ [32]. It should be also mentioned that non-polymeric materials, mainly crystalline solids, have also been proved to change their luminescence upon grinding, smearing, shearing, etc., due to drastic modifications of their crystalline structures [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]. However, in many of these instances, the initial state of the system must be recovered either by recrystallization or by exposing the solid to vapors of a suitable solvent.…”

Moiety effect on the luminescent property of star-shaped triphenylamine (TPA) derivatives as mechanochromic materials

“…1 In the past several years, various MCFs have been reported based on polymers, 2 metal complexes 3 and, in particular, organic dyes for their exible of options in molecule design and rich molecule interactions for tuning their emission properties with an external stimulus. [4][5][6][7][8][9][10][11][12] A twisted conformation is important for organic MCFs owing to their loose packing simultaneously allowing an easy change of the stacking mode in response to an external stimulus, which is better than MCFs with structure disruption caused by chemical bond breaking, and leads to better stability and lifetime. To date, several types of excellent packing mode variation dependent organic MCFs have been reported, including derivatives of tetraphenylethene, 4 9,10-divinylanthracene 4a,5 oligo(pphenylene vinylene), 6 b-diketone boron complexes, 7 pyrene, 8 cyanostyrene, 9 pyran 10 and onium salt.…”

“…To date, several types of excellent packing mode variation dependent organic MCFs have been reported, including derivatives of tetraphenylethene, 4 9,10-divinylanthracene 4a,5 oligo(pphenylene vinylene), 6 b-diketone boron complexes, 7 pyrene, 8 cyanostyrene, 9 pyran 10 and onium salt. 11 These MCF emitters are oen investigated with regard to the tuning of their intermolecular interactions, such as p-p, C-H/p and H-bonding related to their transformation from crystalline to amorphous states, as well as changes with their polymorphs or intramolecular interactions caused by different molecular conformations. [4][5][6][7][8][9][10][11][12] Thus, investigation of the uorescence property of such emitters under an external stimulus can help us to better understand the relationship between the molecular structure and luminescent property, which is very important for mechanochromic analysis and therefore essential for designing novel luminescent materials with MCF activity.…”

“…11 These MCF emitters are oen investigated with regard to the tuning of their intermolecular interactions, such as p-p, C-H/p and H-bonding related to their transformation from crystalline to amorphous states, as well as changes with their polymorphs or intramolecular interactions caused by different molecular conformations. [4][5][6][7][8][9][10][11][12] Thus, investigation of the uorescence property of such emitters under an external stimulus can help us to better understand the relationship between the molecular structure and luminescent property, which is very important for mechanochromic analysis and therefore essential for designing novel luminescent materials with MCF activity. 13 TPA is a typical electron-donor with high hole-mobility and a high uorescent quantum yield; thus, it oen serves as a holetransport material, luminescent emitter or sensitizing dye in optical-electrical elds.…”

Highly Efficient Catalysis of Retro‐Claisen Reactions: From a Quinone Derivative to Functionalized Imidazolium Salts

“…Several experiments that varied the catalyst loading were carriedo ut to evaluate the efficiency of this species( see Table S1 in the Supporting Information), thus showingt hat this catalyst promotes the conversion of the substrate, even with ac atalystl oading of 0.01 mol %t oa chieve at urnover number (TON) of 9800. We think that this new reaction has an enormous impact on organic and organometallic chemistry considering that there are very few examples of imidazolium salts and metal-NHC complexes containing ester groups in the back bone, [16] and therefore this research area has been poorly explored. These imidazolium salts have been obtainedb ys tarting from the imidazole dicarboxylic acid, which is relativelya ffordable, or the carboxylic acid, which is fairly expensive, under strong reaction conditions in several steps.…”