Fluorescence response of cruciform D–π–A–π–D phenothiazine derivatives to mechanical force. Issue 28 (25th June 2019)

• Record Type: Journal Article
• Authors: Zhang, Tong; Zhang, Chunyu; Li, Xiaoting; Liang, Meng; Bian, Weixiao; Zhang, Yan; Wang, Kunpeng; Xue, Pengchong
• Is Part Of: CrystEngComm. Volume 21:Issue 28(2019)
• Page Start: 4192
• Page End: 4199
• Publication Date: 2019-06-25
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c9ce00568d
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : Three kinds of crystals of two phenothiazine derivatives transformed into similar amorphous powders, in which the short-range π-stacking can be deduced by single-crystal structure. Abstract : Two cruciform D–π–A–π–D phenothiazine derivatives with two ester groups as electron-withdrawing moieties ( i.e., EPTD and BPTD, with ethyl and butyl groups, respectively) were synthesized, and their responses to mechanical force stimuli were investigated. EPTD was found to have two polymorphs, namely, EPTD-Y and EPTD-R, with yellow and orange-red fluorescence, respectively. Single-crystal analysis illustrated that strong π-stacking affirmed by a short interplanar distance of 2.98 Å existed in the EPTD-Y crystal, which caused a large red-shift of 72 nm in the absorption spectrum. Meanwhile, although the π-stacking distance reached 3.74 Å, the electrostatic attraction between ester and phenothiazine moieties as an acceptor and donor, respectively, existed in the EPTD-R crystal, which may be responsible for its long emission wavelength. EPTD-R maintained its π-stacking after applying a mechanical force stimulus because its absorption and emission bands only slightly shifted. A fluorescence change from yellow to red occurred for the EPTD-Y crystal after grinding. The spectral results suggested that similar π-stacking existed in EPTD-R and EPTD-Y ground powders and was identical to that in the EPTD-R crystal. In addition, the BPTD crystal emitted green fluorescence due to weak π-stacking induced by a large stacking distance of 4.15 Å. Interestingly, it also changed its fluorescence into red after grinding because of the presence of π-stacking similar to that of the EPTD-R ground solid. Thus, π-stacking can be determined in three amorphous solids.