Photo-responsive cyclodextrin/anthracene/Eu3+ supramolecular assembly for a tunable photochromic multicolor cell label and fluorescent ink†
A photo-responsive supramolecular assembly was successfully constructed through the stoichiometric 2 : 1 non-covalent association of two 4-(anthracen-2-yl)pyridine-2,6-dicarboxylic acid (1) units in one γ-cyclodextrin (γ-CD) cavity, followed by the subsequent coordination polymerization of the γ-CD·12 (12 = two 1) inclusion complex with Eu(III). Interestingly, owing to the photodimerization behavior of anthracene units and the excellent luminescence properties of Eu(III), the Eu3+⊂γ-CD·12 system showed multicolor fluorescence emission from cyan to red by irradiation for 0–16 minutes. Moreover, white light emission with CIE coordinates (0.32 and 0.36) was achieved at 4 min. Importantly, white light-containing multicolor emission could be obtained in water, solid films and living cells. Especially, the Eu3+⊂γ-CD·12 system could tag living cells with marvelous white fluorescence and display no obvious cytotoxicity. Thus, this supramolecular assembly offers a new pathway in the fields of tunable photochromic fluorescent ink and cell labelling.