Mechnofluorochromic properties of N-alkyl amide anthracene derivatives

Several types of N,N′-dialkylanthracene-1,8-dicarboxamides 1 and N-alkylanthracene-1-carboxamides 2 were prepared, and their photophysical properties in the solid state and solution state were observed. N,N′-Di-tert-butylanthracene-1,8-dicarboxamide 1e and N-tert-butylanthracene-1-carboxamide 2e showed slightly high fluorescence quantum yields (φf = 0.63–0.67) in the solid state due to their bulky tert-butyl group. The mechanofluorochromic phenomenon of the N,N′-dialkylanthracene-1,8-dicarboxamide 1 (1,8-bis(N-alkylamide)anthracene) was observed due to the presence of the two amide groups at the 1,8-position of the anthracene ring, because the mechanofluorochromic behavior was not observed for the N-alkylanthracene-1-carboxamide 2 (mono(N-alkylamide)anthracene). Interestingly, changes in the luminous color of the ground samples were observed upon heating and upon fuming with CH2Cl2 vapor, while the pristine samples did not show any change in their fluorescence color under the same conditions.