An efficient approach to diarylethene-amino acid photochromic fluorescent hybrids

An effective approach to the synthesis of diarylethene-amino acid hybrids DE-Gly, DE-AABA and DE-DAA (5a-d - 7-a-d) was developed via condensation of furan-2,5-dione-based diarylethenes (DE) and ethyl esters of glycine (Gly), alpha-aminobutyric acid (AABA) and D-aspartic acid (DAA) with moderate to good yields. According to X-ray diffraction data, DE-Gly hybrid 5a exists in an antiparallel conformation with a distance of 4.549 angstrom between the reactive carbon atoms C(1)-C(11), potentially capable of forming a single bond, which is suitable for the conrotatory photocyclization reaction allowed by the Woodward-Hoffman rules. The structures of the obtained compounds were proved by H-1, COZY, HSQC, HMBC and C-13 NMR spectroscopy. The hybrids DE-Gly, DE-AABA and DE-DAA absorb at 443-456 nm, which corresponds to their existence in a ring-open form O, and display fluorescence at 531-612 nm. Irradiation with light of 436 nm results in their rearrangement into ring-closed colored nonfluorescent isomers C. Backwards re-opening occurs under the action of visible light (lambda > 500 nm). Spectral kinetic investigation of 5a,c revealed that the efficiency of photocyclization, as well as the emission quantum yield, decreases with the growth of solvent polarity. The ring-closed isomer C of sterically hindered 5a (R-2 = R-3 = Me) is stable at room temperature, whereas for 5c (R-3 = H), ring opening readily occurs with the speed increasing with the polarity of the solvent. The internal emission of sterically hindered hybrids 5a, 6a and 7a (R-2 = R-3 = Me) is reversibly modulated in a binary response with good fatigue resistance under successive irradiation with light of 436 and 540 nm. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

An effective approach to synthesize diarylethene-amino acid hybrids DE-Gly, DE-AABA and DE-DAA was developed with moderate to good yields. The structures and properties of the obtained compounds were confirmed by X-ray diffraction and NMR spectroscopy. The hybrids exhibit reversible modulation of internal emission and good fatigue resistance under successive irradiation with light of specific wavelengths.