A spirobifluorene-based supramolecular polymer: Solvent-induced SCSC transformation and fluorescent sensing

Abstract Three crystalline supramolecular polymers (SPs), [(TCPSBF)·(C4H8O2)3]n (intermediate), [(TCPSBF)·(C4H8O2)2]n (UPC-S3) and [(TCPSBF)0.5]n (UPC-S4), were constructed by solvent diffusion method based on 2,2′,7,7′-tetrakis(4- cyanophenyl)-9,9′-spirobi-[9H-fluorene] (TCPSBF). Interestingly, single crystal diffraction and PXRD analyses display the solvent-induced single-crystal-to-single-crystal (SCSC) transformation among three SPs. The unstable intermediate crystal gradually changes to UPC-S3 with the loss of a lattice dioxane molecule at room temperature, and UPC-S3 may be further transformed into UPC-S4 with the loss of the other two lattice dioxane molecules by solvent soaking. Meanwhile, the intermediate crystal can also be directly transformed into UPC-S4 by solvent soaking. As a result, UPC-S4 exhibits highly thermal and chemical stability. The fluorescent spectrum tests show that UPC-S4 possesses potential applications not only in the detecting of small molecules including n-hexane and nitroaromatic derivatives, but also in selective sensing of Fe3+.