A Blueprint for Transforming Indigos to Photoresponsive Molecular Tools

Abstract

Indigo, one of the most ancient and abundant dyes in human history, has recently emerged as a potential functional motif due to its intriguing photochemical properties. This review aims to provide insights into both the preparation of these molecules and their utilization in molecular systems. First, the synthesis of the indigo core as well as available methods to derivatize indigo are described to outline synthetic strategies to build the desired molecular structures. Then, the photochemical behavior of indigos is discussed, with particular focus on E-Z photoisomerization and photoinduced electron transfer. Connections between the molecular structures and their photochemical properties are highlighted and serve as guiding principles for designing indigos to be applied as photoresponsive tools.

Photochromic derivatives of indigo: historical overview of development, challenges and applications

“…The absorption of the photoswitchable indigos covers the spectral range from green to NIR light (≈550–700 nm) making these compounds especially attractive for the design of new biocompatible photochemical tools due to the possibility of performing the switching close to or within the biooptical transparency window (650–900 nm) [ 87 ]. The negative photochromism of indigos, which implies a blue-shift of absorption during the photoreaction, is advantageous for applications in bulk materials because the photoisomers have decreased absorbance at the excitation wavelength [ 9 ]. Depending on the substitution pattern, the quantum yields for the E–Z photoisomerization of indigo photochromes vary from 0.001 to 0.46 and the thermal half-lives of the photoisomers range from seconds to days.…”

“…The toolkit of available synthetic methods makes several types of indigo photoswitches affordable and synthetically accessible. At the same time, the need to develop new synthetic approaches to obtain tailored indigo derivatives remains high [ 9 ]. In contrast to the recent review by Hecht and Huang [ 9 ] providing a detailed analysis of the synthetic methods and describing all types of the photochemical reactions of indigo derivatives ( E–Z photoisomerization, photoinduced proton and electron transfer), our review is focused on the photoswitchable indigo derivatives undergoing the E–Z photoisomerization in view of historical development perspective of these compounds.…”

“…At the same time, the need to develop new synthetic approaches to obtain tailored indigo derivatives remains high [ 9 ]. In contrast to the recent review by Hecht and Huang [ 9 ] providing a detailed analysis of the synthetic methods and describing all types of the photochemical reactions of indigo derivatives ( E–Z photoisomerization, photoinduced proton and electron transfer), our review is focused on the photoswitchable indigo derivatives undergoing the E–Z photoisomerization in view of historical development perspective of these compounds. Additionally, we highlight the recent advances in the photoswitching of the structural derivatives of indigo (indirubin and isoindigo) as well as outline the reported applications of photochromic indigos.…”

“…or non-heme iron oxygenases (naphthalene dioxygenases, multicomponent phenol hydroxylases) [5][6][7][8]. The synthetic approaches towards indigo and its derivatives have been recently reviewed in detail by Hecht and Huang [9].…”

Revisiting Peri‐Aryloxyquinones: From a Forgotten Photochromic System to a Promising Tool for Emerging Applications

“…However, most researchers have been using and further optimizing compounds of these few established compound families, thereby ignoring the fact that there are other, less prominent classes of photoswitches that indeed may offer unique advantages. Among them are for example indigos [141] and indigoids [26b] but also the PAQs reviewed herein can serve as interesting alternatives. From the previous sections it becomes clear that there are some key features of this interesting and often neglected family of photochromic compounds including:…”