Synthesis and Piezofluorochromic Properties of a 2-Substituted Triphenylamine-Anthracene Derivative

Piezofluorochromic organic materials are a class of smart materials with fluorescent change in response to external force stimuli, which have broad application prospects in pressure-sensitive devices, optical information storage and mechanosensory. Triphenylamine with a propeller structure can inhibit strong intermolecular interaction and close packing, which has attracted much attention in piezofluorochromism. A new compound 9, 10-Bis [ 4-( N, N'-diphenylamino) phenyl 1-2methylanthracene ( TPA-MA) with triphenylamine as branch and anthracene-2-methyl as core was prepared from 2methylanthraquinone by zinc powder reduction, bromination with bromineand palladium catalyzed Suzuki coupling reaction, and characterized by H-1 NMR, (13) C NMR and MS. The solvatochromism effect and piezofluorochromic properties were studied by UV-Vis, photoluminescence ( PL), X-ray diffraction ( XRD) spectra, and density functional theory calculation. With the increase of solvent polarity, the absorption spectra of TPA-MA remain almost unchanged, but the PL peak is progressively redshifted, accompanied by the decrease of PL intensity. The Lippert-Mataga plots and the density functional theory calculations reveal that the intramolecular charge transfer (ICT) characteristic of TPA-MA is responsible for the large solvatochromism effect. Meanwhile, TPA-MA has typical piezofluorochromic properties. In the solid state, the PL peak of TPA-MA is at 450 nm with strong blue fluorescence. Upon grinding, the PL peak is red-shifted to 466 nm, accompanied by a decrease in PL intensity. When the ground powder is exposed to dichloromethane vapor or heated to 150 degrees C, it can return to the original blue fluorescence and has repeatability. XRD spectra show that the piezofluorochromic properties of TPA-MA are caused by the change of crystal packing arrangement. The experiments and reported literature indicate that introducing an anthracene 2 -methyl group can further cause a molecular twist in the luminophore skeleton to inhibit the intermolecular interaction and make the crystal packing looser. When triggered by an external mechanical stimulus, the crystalline order is easily destroyed. Consequently, the molecular backbone is more planar under pressure, which enhances the ICT characteristics, resulting in the red-shift and quenching of TPA-MA emission.