Mechanofluorochromism of 1‐Alkanoylaminopyrenes

Abstract

To create a new series of mechanofluorochromic materials and to elucidate the mechanism of the phenomenon of mechanofluorochromism, 1-alkanoylaminopyrenes including 1-acetylaminopyrene (AAPy), 1-octanoylaminopyrene (OAPy), and 1-stearoylaminopyren (SAPy) were prepared. It was found that these materials exhibited mechanofluorochromism with emission colors in the crystalline samples changing reversibly from bluish purple to yellowish green, which could be induced by mechanical grinding. X-ray crystal structure analysis, electronic absorption, and fluorescence spectroscopies, as well as fluorescence lifetime analysis and powder X-ray diffraction analysis of AAPy suggested that the present mechanofluorochromism was caused by developing crystal defects through grinding. Intermolecular hydrogen bonds were suggested to play an important role in the occurrence of mechanofluorochromism, suppressing the face-to-face overlapping of pyrene moieties to form excimers in the pristine crystal.

Mechanochromic Luminescence from Crystals Consisting of Intermolecular Hydrogen‐Bonded Sheets

“…Because AIE‐active luminophores tend to form loosely‐packed assemblies, mechanical stimuli induces closed‐packing and/or conformational changes, which alter their photoluminescence properties. Another promising approach is the design of molecular structures in which different types of intermolecular interactions can compete against each other . Adopting this strategy, molecules can form several thermodynamically ( meta )stable assembled states and mechanical stimuli can induce interconversions among these states.…”

“…Adopting this strategy, molecules can form several thermodynamically ( meta )stable assembled states and mechanical stimuli can induce interconversions among these states. In particular, competition between hydrogen‐bonding and π–π stacking is effectively achieved by introducing amide groups directly into luminophores . This effectiveness is attributed to the fact that the length between amide groups forming hydrogen bonds is generally longer than the distance between aromatic groups forming π–π stacks.…”

Mechano‐ and Photoresponsive Behavior of a Bis(cyanostyryl)benzene Fluorophore

“…Not only av ariety of simple molecular systems, but mechanochromic luminescents upramolecular systemsa nd self-assembled dyad molecule with dual sensitivity of photo-andm echanochromism have also been reported. [6] Nakano and co-workers have recently reported two series of mechanochromic luminescent materials [7,8] and demonstrated with as eries of diarylaminobenzaldehyde-based amorphous molecular materials that the mechanical inductiono fl arge conformational changes of excited molecules can give rise to mechanoresponsive luminescence. [7] As eries of mono-substituted pyrenesw as used to show that mechanochromic emission can be caused by formation of defects by grinding the crystalline samples, which allows for the excimer formation.…”

“…[7] As eries of mono-substituted pyrenesw as used to show that mechanochromic emission can be caused by formation of defects by grinding the crystalline samples, which allows for the excimer formation. [8] Molecular materials based on bis(cyanostyryl)benzene chromophores have also been widely exploited as basis for mechanoresponsive effects, because these molecules can adopta range of solid-state structurest hat give rise to multicolor emission. In as eries of studies, the Wederg roup hasb lended small amountso fb is(cyanostyryl)benzene derivatives with polymers and shown that tensile deformation leads to ab reakage of dye aggregates and, thus, ac hange from excimer-dominated to monomer-rich emission.…”

Multiple Photoluminescent Processes from Pyrene Derivatives with Aggregation‐ and Mechano‐Induced Excimer Emission

“…[14,[20][21][22][23] Regarding the emission in the solid state, variousk inds of mechanochromic illuminants based on pyrene derivates have been reported, which are accompanied by excimer-to-excimer,m onomer-to-excimer and conformation transitions. [24][25][26][27][28][29][30][31] Accordingly,i ti safacile and efficient method to use mechano-inducede xcimer emissiont oo btain excimer luminescence in the solid state.…”