Photochromic dyes represent a specific class of molecules that can undergo reversible transformations upon exposure to light between isomers that possess different optical properties. This particular characteristic makes them interesting for a wide range of applications, from bioimaging to data storage, detection or optical lenses.

We designed and synthesized four new photosensitizers with a donor-pi-acceptor structure incorporating SINO and NIPS units as photochromic cores. Their optical, photochromic and acidochromic properties were thoroughly studied to establish structure-property relationships. Then, after disentangling the possible forms adopted as a function of stimuli, their photovoltaic properties were evaluated in DSSCs. Although photochromic behavior is not always preserved, we elucidate the interaction between photochromic, acidochromic and photovoltaic properties and demonstrate that these dyes can act as photosensitizers in DSSCs. We report a maximum energy conversion efficiency of 2.7% with a NIPS-based dye, a tenfold improvement over previous work on a similar class of compounds.

This work opens new perspectives of developments for SINO and NIPS in optical and photovoltaic devices, and it provides novel research directions to design photochromic materials with improved characteristics..