A photochromic Cd(ii)-organic framework showing highly efficient dual-response sensing properties

Abstract

Photochromic materials have been found to be promising for a broad range of applications. However, it remains a great challenge to develop new photochromic materials. In this work, a dihydroanthracene-based photochromic organic molecule 9,10-bis(di(pyridine-4-yl)methylene)-9,10-dihydroanthracene (L) was developed as a functional ligand to construct a LMOF-based sensor material [Cd₂L(HBTC)₂·2H₂O·2i-PrOH]_n (1) (LMOF = luminescent metal–organic framework; H₃BTC = benzene-1,3,5-tricarboxylic acid; i-PrOH = isopropanol). 1 is constructed using a 6-connected [Cd₂(COO)₂]²⁺ cluster, a 4-connected L unit and a HBTC double-bridge and exhibits a two-dimensional (2-D) (4,6)-connected architecture. 1 has good water and thermal stability. Before and after photochromism, this LMOF exhibits different luminescence properties, which results in dual-response and highly selective sensing properties. 1 can detect TNP with high sensitivity and selectivity in aqueous media by luminescence quenching effects. More importantly, 1′ (1 after photochromism) shows ultrahigh sensing sensitivity and selectivity towards MnO₄⁻ (the second highest K_sv of 4.08 × 10⁵ M⁻¹). Furthermore, 1′ can identify MnO₄⁻ in the presence of a similar strong oxidizing anion Cr₂O₇²⁻. In addition, quenching sensing mechanisms are discussed in detail. This work will contribute to the development of highly efficient dual-response sensors.