Synthesis and photochromism of new asymmetrical diarylethenes with a variable heteroaryl ring and a quinoline unit

Three new asymmetrical photochromic diarylethenes containing a variable heteroaryl ring and a quinoline unit were synthesized and their structures were determined by single -crystal X-ray diffraction analysis. Their properties, including photochromism, acidichromism, and fluorescence, were investigated systematically. For these diarylethenes, the one with an indole moiety had the largest absorption maximum, cyclization quantum yield, photoconversion ratio, emission peak, and fluorescent modulation efficiency. In addition, these diarylethenes exhibited an evident dual switching behavior induced by the stimulation of acid/base and UV/Vis. Addition of trifluoroacetic acid to solution of the diarylethenes produced protonated derivatives with notable changes in their absorption spectra. These results indicated that the effect of the heteroaryl rings played a very important role during the process of photoisomerization for these diarylethene derivatives.