O-Methylphenyl modified tetraphenylethene: Crystalline-induced luminous blue-shift and stimuli-responsive luminescence color switching

Abstract

Organic solid-state luminescence switching materials have attracted increasing interest due to their ability to manifest a reversible solid-state luminescence color change upon physical perturbation without changing the chemical structure of their component molecules. We employed the design strategy of introducing different weak C–H···π interactions into the same molecular system to obtain two metastable solid states and synthesized an o-methylphenyl substituted tetraphenylethene molecule: 1,1,2,2-tetrakis(2′-methyl-[1,1′-biphenyl]−4-yl)-ethene (TMPE). This compound showed typical aggregation-induced emission properties and a crystalline-induced luminous blue-shifted feature. The results of single-crystal structure determination and theoretical calculation indicated that the blue-shift was caused by the large twisted configuration of biphenyl units fixed by the C–H···π interactions in the crystal state. Furthermore, the compound TMPE exhibited reversible stimuli-responsive luminescence color switching between blue emission (459nm) in the crystal state and green emission (496nm) in the amorphous state upon fuming, grinding and heating. This work discusses the relationship between the molecular stacking mode and the photophysical properties of the compound. The X-ray single-crystal structures, characterization of the photophysical properties, powder X-ray diffraction and differential scanning calorimetry provide insight into the phase transformation and the luminescence behavior. The obvious luminescent color, high luminescent efficiency and manageable, reversible fluorescence switching give TMPE the potential to be the foundation of a class of smart organic solid luminescence switching materials.