(15)N CP/MAS NMR as a Tool for the Mechanistic Study of Mechanical Stimuli-Responsive Materials: Evidence for the Conformational Change of an Emissive Dimethylacridane Derivative

[Image: see text] Mechanochromic luminescent molecules are currently attracting considerable attention because of their promising technological applications, but understanding their mechanism of action is challenging and is thus hindering our deeper understanding of these materials. The conformational change of 9,9′-dimethyl-9,10-dihydroacridane derivative 1 was examined using solid-state (15)N nuclear magnetic resonance (NMR) spectroscopic techniques without using a specifically (15)N-labeled compound. A difference between the two conformers was clearly observed in the measurements and was assigned to the ⟨pl⟩ and ⟨bf⟩ spatial structures. The results were supported by quantum chemical calculations on (15)N NMR chemical shifts of each isomer. The technique presented here can clearly identify the structural changes caused by crushing a powder sample. Such structural changes are difficult to determine using X-ray diffraction (XRD) measurements.