Molecular design for the highly-sensitive piezochromic fluorophores with tri-armed framework containing triphenyl-quinoline moiety

• Two piezofluorochromic compounds with novel tri-arm architecture were prepared.
• The new compounds have extremely sensitivity toward external pressure.
• By gentle grinding, one compound showed a large fluorescent shift of 112 nm.
• The magnitude of the fluorescence shift strongly depends on the size of the arm.
• The two new compounds also vary their fluorescence under solvent annealing.

Two tri-armed piezochromic fluorescent molecules of tris(4-(4-phenylquinolin-2-yl)phenyl)amine (TPA-3Qu) and tris(4-(6-(9H-carbazol-9-yl)-4-phenylquinolin-2-yl)phenyl)amine (TPA-3QuCz) were prepared and found to exhibit keen fluorescence responses toward compression. With the framework of a twisted, pyramidal triphenylamine (TPA) center connecting to three large quinolinecarbazole (QuCz) arms, the amorphous TPA-3QuCz exhibited a large bathochromic shift of 112 nm under gentle grinding forces, which is different from the small shift of 32 nm for TPA-3Qu under applying a relatively-large pressure of 10 MPa. Conformational transformations involving planarization of the arms were proposed to account for the observed fluorescence responses of TPA-3QuCz and TPA-3Qu towards pressure.

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