Iodine-catalysed synthesis of a novel meso-substituted dipyrromethane and its evaluation as a cation chemosensor

In recent years, meso-substituted dipyrromethanes have been frequently explored as potential ion sensors. Some of these compounds exhibit very interesting photophysical properties, which can be triggered in the presence of some ions and display chromogenic and/or fluorescence changes. However, most common methods for the synthesis of these molecules can be laborious and time-consuming, requiring a great excess of pyrrole and a tightly controlled atmosphere. Recently, a new method based on molecular iodine-catalysis has been proposed as a fast, inexpensive and good-yielding procedure with reduced reaction times. Using molecular iodine as a catalyst withdraws the requirement of strong and expensive acid-catalysts, such as TFA. Here we report the synthesis and characterization of a dipyrromethane functionalised with an arylthiophene bridge, by using the iodine catalytic method. The compound was obtained in the solid state in 60% yield. Evaluation of the chemosensory ability in the presence of several cations showed both chromogenic and fluorescent response, with Fe³⁺, Cu²⁺, Hg²⁺ and Cr³⁺ among the most easily detected ions.