Mechanochromic Luminescence from Crystals Consisting of Intermolecular Hydrogen‐Bonded Sheets

Abstract

Introduction of functional groups that can form intermolecular hydrogen bonds into highly‐emissive luminophores is a promising way to induce mechanochromic luminescence. Herein, we report that a 9,10‐bis(phenylethynyl)anthracene derivative featuring two amide groups forms green‐emissive crystals based on two‐dimensional hydrogen‐bonded molecular sheets. Mechanical grinding changed the emission from green to yellow, owing to a transition from a crystalline to an amorphous phase. Infrared spectroscopy revealed that mechanical stimuli disrupted the linear hydrogen‐bonding formation. A thermal treatment recovered the original green photoluminescence.

Optimizing the self‐assembly of conjugated polymers and small molecules through structurally programmed non‐covalent control

“…77 By analyzing the intermolecular interactions in crystal structures of isolated polymorphs, researchers have determined that mechanical force can disrupt hydrogen bonding interactions, changing the luminescence of small molecular solids. 78,79 For example, Sudhakar et al recently described the mechanofluorochromic behavior of a series of donor-acceptor borylated aryl amines for use in OLEDs and sensors. 80 Each compound possessed the same general conjugated structure (Figure 4), but differed in the number, regiochemistry, and substitution of amine groups able to form hydrogen bonding interactions.…”

“…One example is mechanofluorochromism (MFC), in which a material changes luminescence upon exposure to mechanical force often through transitioning through one or more other accessible polymorphs 77 . By analyzing the intermolecular interactions in crystal structures of isolated polymorphs, researchers have determined that mechanical force can disrupt hydrogen bonding interactions, changing the luminescence of small molecular solids 78,79 . For example, Sudhakar et al recently described the mechanofluorochromic behavior of a series of donor‐acceptor borylated aryl amines for use in OLEDs and sensors 80 .…”

Mechanical and thermal stimuli-induced release of toluene included in luminescent crystals as one-dimensional solvent channels

“…Furthermore, the competing effects of hydrogen bonding and π-π stacking result in several thermodynamically (meta)stable states that can be converted from one form to another by thermal treatment, mechanical stimuli, and exposure to solvent vapour. 31,35,38,39,47,54,65,86,87 This is because the length between functional groups forming hydrogen bonds is generally longer than the distance between aromatic moieties constructing π-π stacked structures. 31,35,38,65 Since it was discovered that a 1,3,6,8tetraphenylpyrene derivative having four hexylamide groups was found to show mechanochromic luminescence, 31 several organic compounds have been reported to form hydrogen bonds in their molecular assemblies and change their emission colours in response to mechanical and thermal stimuli.…”

Fluorinated Tolane Dyads with Alkylene Linkage: Synthesis and Evaluation of Photophysical Characteristics

“…In addition to significant advances being made in the field of solid-state light-emitting molecules, it has been increasingly noted that many unique luminescence materials show a change in the 2 of 16 luminescence color or intensity when an external stimulus is applied. These have therefore been named stimulus-responsive photoluminescent molecules [16][17][18][19][20][21]. In spite of their wide utility, progress in terms of the molecular design of solid-state photoluminescent molecules has been quite limited; accordingly, the search for efficient solid-state photoluminescent molecules is still on.…”

“…Crystals 2020, 10, x FOR PEER REVIEW 2 of 16 responsive photoluminescent molecules [16][17][18][19][20][21]. In spite of their wide utility, progress in terms of the molecular design of solid-state photoluminescent molecules has been quite limited; accordingly, the search for efficient solid-state photoluminescent molecules is still on.…”