Design and synthesis of a deep-cavity aluminium-organic macrocycle to trap dyes and generate enhanced non-linear optical performance

Abstract

The development of a “two birds with one stone” strategy for capturing pollutant molecules and incorporating new functions provides a promising solution for sustainability. In this work, we designed an unprecedented deep-cavity aluminum–organic macrocycle to trap dye molecules and enhance non-linear optical performance. Using long building blocks and inorganic aluminum ions at the midriff, we successfully isolated a deep-cavity (1.8 nm) macrocycle, with a deeper cavity than classic pure organic macrocycles, such as crown ether and calixarenes. We report the accurate locking of the HAO7 dye molecule in the deep-cavity macrocycle and reveal its trapping mechanism at the molecular level for the first time. The combined host–guest compound AlOC-136-HAO7 displays altered physical properties, such as a decreased optical band gap and increased proton conductivity but also exhibits enhanced third-order non-linear optical (NLO) properties. Combined with theoretical calculations, we confirmed that the enhancement was attributed to abundant host–guest interactions and the guest-to-guest charge transfer. Our findings provide a strategy for isolating deep-cavity macrocycles and further demonstrate their enormous potential for capturing contaminants and forming valuable materials.