Polymorphism-Dependent and Switchable Emission of Butterfly-Like Bis(diarylmethylene)dihydroanthracenes

Abstract

Organic fluorophores with reversible emission switching behavior are promising materials for applications in sensors, optical recording, security inks, and optoelectronics. A variety of aggregation-induced emission (AIE) luminogens with mechanochromic luminescence has been prepared, and the transformation of efficient bluer-emitting crystals to amorphous powders with redder and weaker emission is proposed to be the cause for such behavior. However, detailed mechanistic understanding from experimental to theoretical is lacking. In this work, we present the design and synthesis of a group of bis­(diarylmethylene)­dihydroanthracenes with butterfly-like shapes. These molecules exhibit aggregation-induced emission characteristics due to the restriction of intramolecular motion in the aggregated state. They show mechanochromism, because of the transformation between crystal and amorphous states with different colors and efficiencies aided by grinding/heating or solvent fuming processes. By investigation of their single-crystal structures and theoretical calculations, the loose molecular packing with noncovalent intermolecular interactions, the extent of conformational twisting, and the packing density of the luminogens, as well as freedom of intermolecular motion in the excited state, are stemmed for their reversible polymorphism-dependent emission behaviors.

The butterfly effect in bisfluorenylidene-based dihydroacenes: aggregation induced emission and spin switching

“…This is attributed to the increase in steric bulk of the uorene moiety. 23 As shown in Fig. S2, † the acene backbones also display a typical quinoidal structurefor example in bFA, C1-C15 and C8-C28 have double bond character ($1.35Å) while C1-C2, C1-C14, C8-C7, and C8-C9 have single bond character ($1.49Å).…”

“…[18][19][20][21] Through precise molecular engineering of the core structure of oligoacenes, Tang and co-workers have shown that quinoidal derivatives of oligoacenes can exhibit aggregation induced restricted intramolecular vibration (RIV). 22,23 AIE is counterintuitive since aggregation tends to quench photoluminescence of organic chromophores. [24][25][26] For example, bis(diphenylmethylene)dihydroacenes are non-emissive in solution, but upon aggregation, they uoresce in the solid state ( Fig.…”

Tricolor Luminescence Switching by Thermal and Mechanical Stimuli in the Crystal Polymorphs of Pyridyl‐substituted Fluorene

“…[1,2] The luminescence properties of organic solids dependo nn ot only the molecular chemical structure, but also on moleculars tacking. [3,4] In recent years, a number of stimuli-responsive organic fluorescent materials have been reported, [5,6] in which switching to the solid luminescent color is achieved by alteringt he mode of molecularly assembled structures upon externals timulus, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] such as grinding, heating, and exposure to chemicalv apor.T his smart approacht oc hanging the luminescence properties of organic solids is thought to be more promising and easier than switching molecularly chemical structures by chemical reactions. To date, most of the reported examples display ar eversible twocolor luminescence switching, [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] and multicolor switched materials remaine xtremelyl acking due to the un-designability of this kind of smart materials.…”

Multistimuli Response and Polymorphism of a Novel Tetraphenylethylene Derivative

“…These three different states of 1 can be interconverted into each other rapidly with simple treatments. This property is rarely reported and it provides more promising application potentials than other known molecules …”