Path-independent all-visible orthogonal photoswitching for applications in multi-photochromic polymers and molecular computing

Synthetic molecular photoswitches have taken center stage as high-precision tools to introduce light-responsiveness at the smallest scales. Today they are found in all areas of applied chemistry, covering materials research, chemical biology, catalysis, or nanotechnology. For a next step of applicability truly orthogonal photoswitching is highly desirable but to date such fully independent addressability of different photoswitches remains to be extremely challenging. In this work we present the first example of all-visible, all-light responsive, path independent, and fully orthogonal photoswitching. By combining two recently developed indigoid photoswitches - peri-anthracenethioindigo and rhodanine-based chromophore - a four-state system is established and each state can be accessed in very high yields completely independently and also with visible light irradiation only. The four states give rise to four different colors, which can be transferred to a solid polymer matrix yielding a multi-state photochromic material of high versatility. Further, combination with a fluorescent dye as third component is possible elevating applicability in all-photonic molecular logic behavior and information processing with this orthogonal photoswitching system.