Constructing a Nonfluorescent Conformation of AIEgen: A Tetraphenylethene Embedded in the Calix[4]arene's Skeleton

Two novel 1,1-diphenylmethylidene decorated calix[4]arenes, (Calix-DPE(OCH3)(4) and Calix-DPE(OH)(4)), were designed and prepared. The tetraphenylethene (TPE) unit is embedded in the calix[4]arenes skeleton, so the conformation of tetraphenylethene unit is significantly affected by the conformation of calix[4]arene. Unlike the Calix-DPE(OCH3)(4), the Calix-DPE(OH)(4) does not show the aggregation-induced emission (AIE) phenomena in solution or the crystal state because of the presence of intramolecular hydrogen bonding, which leads to a cone conformation for the calix[4]arene skeleton in which the embedded phenyl rings of the TPE have to take an almost perpendicular configuration to the C=C bond. This result provides direct evidence that the maximal cross-chromophore pi-conjugation within the tetraphenylethene is one of the prerequisites of switching on its AIE. This offers the possibility of switching the emission of TPE by conformation changes.