Highly Fluorescent Thienoviologen-Based Polymer Gels for Single Layer Electrofluorochromic Devices

A highly fluorescent electrofluorochromic gel with quantum yields as high as 67% is prepared by incorporating the thienoviologen fluorophore 4,4'-(2,2'-bithiophene-5,5'-diyl)bis(1-nonylpridinium)bistriflimide into a polymeric matrix. The fluorescent emission spectrum of the gel at low percentages of thienoviologen shows a strong band at 530 nm. A new intense fluorescence band at 630 nm can be induced by fluorophore aggregation. Single layer electrofluorochromic devices were readily prepared by sandwiching the polymer gels between two indium tin oxide (ITO) electrodes. The fluorescence intensity can be easily modulated between a fluorescent and a quenched state, in a wide visible spectral range, by direct electrochemical reduction of the thienoviologen fluorophore. It exhibits three reduction states, each with different emission properties. The reversible interconversion among these states leads to a high electrofluorochromic stability of the device, exhibiting switching times of a few seconds and, to the best of our knowledge, the highest contrast ratio (337).