Selectivity via insertion: Detection of dicarboxylic acids in water by a new film chemosensor with enhanced properties

A novel fluorescence film sensor was designed and prepared to improve the performance of the film sensors reported recently for dicarboxylic acids. The reported sensors suffered from slow response and low sensitivity to the analytes. Simple elongation of the spacer by using 1,4-diaminobutane instead of 1,2-diaminoethane or 1,3-diaminopropane improved the performances of the film sensors greatly. The response time was reduced from tens of minutes, or even hundreds of minutes to less than 10 min, and the sensitivity was improved from more than 10 mM to tens of micro-molars. Similar to the reported films, the new film also shows combined monomer and excimer emission of pyrene (Py) both in wet and dry states, and both the emissions in the monomer and excimer regions increases along with addition of dicarbonxylic acids. The excimer formed in the present film, however, mainly adopts, especially in aqueous phase, sandwich-like structure. The differences in the photophysical behavior and the improvement in the sensing performance mentioned above have been attributed to the increase in the length of the spacer, which makes the spacer in the present film more flexible and gives the sensing molecule more chance to form perfect excimers. Furthermore, the response of the film to dicarboxylic acids is well reversible.