Remarkable responsive behaviors of iso-aminobenzopyranoxanthenes: protonation effect, photochromism and piezochromism

The iso-cis/trans-aminobenzopyranoxanthenes (iso-cis/trans-ABPXs), as one of popular leuco dyes, were investigated in solution or crystal phase. The introduction of benzo-pentacyclic-ester group in iso-cis/trans-ABPXs leads to remarkable multi-stimuli responsive behaviors, including protonation effect, photochromism and piezochromism with notable color changes. The iso-cis/trans-ABPXs show different in the responsive sensitivity and the iso-cis-ABPX is highly sensitive to environmental stimuli relative to the trans-form, which can be explained by their different C-H center dot center dot center dot O interaction and/or C-O bond length. Interestingly, as the ultraviolet light irradiation time increasing, the iso-cis/trans-ABPXs solution gradually becomes transparent and orange precipitates are achieved, which is identified as iso-ABPXs. Multi-stimuli responsive behaviors on the iso-cis/trans-ABPXs(+/-) provide a comprehensive insight into the chromogenic mechanisms of this type of materials, suggesting that they may be potential candidate materials for sensors and indicators.