Dual-emission and thermochromic luminescence alkaline earth metal coordination polymers and their blend films with polyvinylidene fluoride for detecting nitrobenzene vapor

Dual emission materials show unique advantages in the areas of detecting analytes or probing a change of environment (e.g. temperature or pressure). In this study, we have harvested three coordination polymers (CPs), [Ca(H₂EBTC)(DMF)₂] (1), [Sr₃(EBTC)₂(DMSO)₂] (2) and [Ba₃(HEBTC)₂(DMSO)₂] (3) with H₄EBTC = 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid, which emit H₄EBTC-based fluorescence and phosphorescence under ambient conditions and show thermochromic luminescence behavior in the range 10-300 K. The luminescent blend films of 1-3 with hydrophobic polyvinylidene fluoride (PVDF), labeled as X@PVDF (X = 1-3), were fabricated using a facile and effective drop-casting approach. The formation of blend films much improves the water-stability of alkaline earth metal CPs. The dual emission blend films of CPs were used as the signal transducer for nitrobenzene vapor detection for the first time. Compared to the conventional luminescence probe that used a dispersed solution of luminescent CP powder, the dual emission blend films show excellent performances, e.g. ultrafast luminescence quenching response, lower concentration limit of detection, facile manipulation and cycling utility. Such a strategy using a blend film as the probe can be easily expanded to other probe systems of luminescent CPs, thus opening up a new perspective for the development of efficient and practical film sensing materials.