Herein, we synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridges. Owing to the charge transfer emission, the solid-state photoluminescence quantum yield (Φ_PL) was enhanced compared with that of the parent pillar[6]arene (Φ_PL=0.063→Φ_PL=0.36). Furthermore, it displayed a turn-off sensing toward nitrobenzene (NB) vapor; a fluorescence quenching was observed when exposed to the NB vapor.

Abstract

Macrocyclic arenes show conformational adaptability, which allows host–guest complexations with the size-matched guest molecules. However, their emission properties are often poor in the solid states due to the self-absorption. Herein, we newly synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridging structures. Solvatochromic study reveals that the nitrogen-embedding into the cyclic structures can strengthen the intramolecular charge transfer (CT) nature compared to that of the linear nitrogen-bridged precursor. Owing to the large Stokes shift in the solid state, one of the nitrogen-embedded pillar[6]arenes shows high absolute photoluminescence quantum yield (Φ_PL=0.36). Furthermore, it displays a turn-off sensing ability toward nitrobenzene (NB) vapor; a fluorescence quenching is observed when exposed to the NB vapor. From the structural analysis before and after the exposure of NB vapor, the amorphous nitrogen-embedded pillar[6]arene efficiently co-crystallize with NB and formed non-emissive intermolecular CT complexes with NB.