Piezofluorochromic properties of AIE-active 9,10-bis(N-alkylpheno-thiazin-3-yl-vinyl-2)anthracenes with different length of alkyl chains

• A series of PT-Cn with different length of N-alkyl chains are synthesized.
• PFC spectral shifts (ΔλPFC) of PT-Cn increase with the increase of alkyl length.
• PT-Cn homologs become new alkyl chain length-dependent PFC materials.
• A remarkable ΔλPFC up to 71 nm for PT-C18 is observed.

9,10-Bis(N-alkylphenothiazin-3-yl-vinyl-2)anthracenes (PT-Cn) with different carbon numbers (n) of alkyl chains (n = 2, 3, 5, 6, 7, 9, 12, 18) are prepared to further understand the effect of alkyl lengths on the solid-state fluorescence and piezochromic luminescence of alkyl-containing 9,10-bis(arylvinyl)anthracenes. The results show that the fluorescence emissions of both pressed and annealed PT-Cn are gradually blue-shifted, but the blue-shifted amplitudes of annealed states are more remarkable with the increase of alkyl length, leading to that longer alkyl-containing PT-Cn show larger piezofluorochromism (PFC) spectral shifts. Powder wide-angle X-ray diffraction and differential scanning calorimetry experiments reveal that the transformation between crystalline and amorphous states under various external stimuli is responsible for the PFC and restoration behaviors. This work demonstrates once again that combining the simple alternation of molecular chemical structure and the physical change of aggregate morphology under external stimuli could tune the solid-state optical properties of some organic fluorophores.

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