Fig. 1: Indigoid chromophores and extended structural realm of diaryl-HIs as multi-stimuli four-state switches.
a Monoaryl-HIs provide limited structural and functional diversity (proton highlighted in light gray) of previous works. Related higher substituted HTIs enable numerous advanced applications if the proton is replaced by R1 (highlighted in light blue). b A short and high yielding synthetic access to diaryl-HIs unlocks a plethora of advanced properties (four red arrows, H replaced by aromatic R1 highlighted in red), such as green and red-light responsiveness, significant photochromism and color contrasts, high isomer ratios in the photostationary state (pss), high thermal bistability, and applicability of these properties in advanced polymer materials. Aniline-based diaryl-HI chromophores possess two additional protonated switching states. This allows four state switching using the stimuli green light, red light, temperature, acid, and base. This multi-stimuli capability allows to enrich each of the four states individually. Blue-colored structures possess hypsochromic shifted absorption spectra, red-colored structures possess bathochromic shifted absorption, and purple-colored structures are related to protonated species appearing purple to the human eye. Source data are provided in a Source Data file.
