Vintages for New Fashion: Red-Shifted Photoswitching via the Triplet-Photoreaction Channel with Charge-Transfer Complex Sensitizers

Triplet-sensitization has been proven invaluable for creating photoswitches operated over a full visible-light spectrum. While designing efficient triplet-sensitizers is crucial for establishing visible-light photochromism, it remains an appealing yet challenging task. In this work, we propose a versatile strategy to fabricate triplet-sensitizers with intermolecular charge-transfer complexes (CTCs). Through fine-tuning interactions between various donor and acceptor units, a series of CTC sensitizers were prepared with intensified visible-light absorption and a distinctive narrow ΔE_ST feature. By virtue of this, a bidirectional visible-light photochromism (475 nm/605 nm) was achieved via integrating CTC sensitizers with classic diarylethene (DAE) photoswitches in various substrates upon triplet photoreaction pathways. Proof-of-concept applications, such as photoresponsive printing and mechanic-facilitated inkpad, were subsequently presented. The flexible accessibility and tunability of CTC sensitizers facilitate both generalized and customized production of photoresponsive systems that operate within the visible-light region.