Mechanofluorochromic properties of fluorenone-based triphenylamine- functionalized chalcone derivatives and their
Baobei Liu1, Hanrong Liu1, Yanru Su1
1Key Laboratory of Magnetic Molecules and Magnetic Information Material of Ministry of Education, College of Chemistry and Chemical Engineering, Shanxi Normal University, Taiyuan, 030032, PR China.
Abstract:
In this study, three new aggregation-induced emission (AIE)-active chalcone derivatives based on triphenylamine and fluorenone, namely (E)-2-(4-(3-(4-(diphenylamino)phenyl)acryloyl)phenyl)-9H-fluoren-9-one (DPAPF), (E)-2-(4-(3-(4-(bis(4-bromophenyl)amino)phenyl)acryloyl)phenyl)-9H-fluoren-9-one(BAPAPF), and (E)-2-(4-(3-(4-(bis(4-bromophenyl)amino)phenyl)acryloyl)phenyl)-9H-fluoren-9-one (DTPAPF), have been designed, synthesized and fully characterized. Photophysical investigations and theoretical calculations revealed that these donor-acceptor (D-A) molecules adopt highly distorted non-planar conformations and exhibit distinct intramolecular charge transfer (ICT) characteristics. All three compounds display remarkable AIE properties in DMF/H₂O binary solvent mixtures. Moreover, DPAPF, BAPAPF and DTPAPF exhibit obvious mechanofluorochromic (MFC) behavior, upon grinding, their emission maxima show significant bathochromic shifts of 48 nm, 24 nm, and 62 nm, respectively. Powder X-ray diffraction (PXRD) and field-emission scanning electron microscopy (FESEM) analyses confirm that the reversible MFC response originates from crystal-to-amorphous phase transitions in the solid state. Single-crystal structural analysis further reveals that weak intermolecular interactions can be readily disrupted by external mechanical force, which favors the MFC effect. The planarization of molecular conformations and the subsequent planar intramolecular charge transfer (PICT) process are proposed to be responsible for the bathochromic shift upon grinding. Benefiting from their reversible high-contrast mechanofluorochromism, these luminogens demonstrate excellent application potential in anti-counterfeiting and multi-level information encryption.
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