We report mechanochromic color change controlled by conformational change (between folded and twisted conformers) of fluorenylidene-acridanes (FAs). FAs with four N-alkyl groups (methyl, ethyl, n-butyl and n-octyl) were synthesized via the Barton–Kellogg reaction of diazofluorene and electrophilic N-tert-butoxy carbonyl thioacridone, deprotection of the tert-butoxy carbonyl group gives fluorenylacridine, and alkylation on the nitrogen atom is done using alkyl tosylate or triflate. FAs were characterized by NMR, UV-vis absorption and photoluminescence spectroscopy, theoretical calculation, cyclic voltammetry, and powder and single-crystal X-ray analyses. The color and folded/twisted conformation of the FAs were changed by the choice of substituent on the nitrogen atom, physical state (solution or solid), and morphology (crystalline or amorphous). Grinding of N-methyl FA solids, using an agate mortar, caused the morphology to change from a crystalline to amorphous state, which induced a conformational change from the folded to the twisted conformer, and a mechanochromic color change from yellow to dark green. The reverse color change, along with a morphological and conformational change to the folded conformer, was performed by solvent vapor exposure (chloroform). The twisted and folded conformers showed ambipolar (hole/electron) and hole-only transport properties, respectively.

中文翻译：

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芴基-ac啶烷在研磨时颜色变深–通过构象变化产生的基态机械致变色†

我们报告了由亚芴基ac啶酮（FAs）的构象变化（折叠和扭曲的构象异构体之间）控制的机械变色颜色变化。具有四个的FA ñ -烷基（甲基，乙基，Ñ丁基和Ñ辛基）的合成经由diazofluorene和亲电的巴顿凯洛格反应N-叔丁氧基羰基硫代吖啶酮，所述的脱保护叔-丁氧基羰基产生芴基ac啶，并且在氮原子上的烷基化是使用甲苯磺酸烷基酯或三氟甲磺酸酯进行的。FAs的特征在于NMR，UV-vis吸收和光致发光光谱，理论计算，循环伏安法以及粉末和单晶X射线分析。通过选择氮原子上的取代基，物理状态（溶液或固体）和形态（晶体或无定形），可以改变FA的颜色和折叠/扭曲结构。N的研磨-使用玛瑙研钵的甲基FA固体导致形态从结晶态变为无定形，从而导致构象从折叠的构象变为扭曲的构象，而机械变色的颜色从黄变为深绿色。通过溶剂蒸气暴露（氯仿）进行相反的颜色变化，以及折叠的构象物的形态和构象变化。扭曲和折叠的构象异构体分别显示出双极性（空穴/电子）和仅空穴的传输性质。