Synthesis and photochromic properties of novel pyridine-containing diarylethenes

Three isomeric pyridine-containing diarylethenes were synthesized to study the effects of nitrogen atom position (ortho, para, meta) on their photochromic properties. Among these diarylethenes, the example with the nitrogen atom at the ortho-position of pyridine displayed the largest absorption maximum and molar absorption coefficients. The cyclization quantum yields increased in order of para < meta < ortho, whereas their cycloreversion quantum yields decreased in order of para > meta > ortho. Compared to the diarylethene with terminal phenyl ring, those with a terminal pyridine showed enhanced cyclization quantum yields and emission intensities. Moreover, these pyridine-containing diarylethenes exhibited multi-addressable switching behavior under the stimulation of both proton and light. Addition of trifluoroacetic acid to the solutions of the diarylethenes resulted in notable color change, and their N-protonated forms also possessed excellent photochromism. These results indicated that the nitrogen atom position played a pivotal role in the process of photoisomerization of the diarylethenes. (C) 2012 Elsevier Ltd. All rights reserved.