JACS: molecular optical switch based on spiropyran

Photochromic molecules, also known as molecular light switches, are widely used in optical data storage, light activated drugs, intelligent materials and super-resolution microscopes The common photochromic skeletons are spiropyran, azobenzene, diarylethene and fumaramide At present, it has become a research hotspot to construct multi responsive photochromic materials with multiple isomers by covalent bonding two or more individual optical switch molecules These chromotropic materials usually contain azobenzene (CIS trans isomerization), diarylethene (CIS trans isomerization) or spiropyran (spiropyran blue isomerization) structures Therefore, it is very urgent to design photochromic skeletons with simultaneous cis - trans and spiro - cyano isomerization Recently, Professor Joakim Andr é asson of Chalmers University of technology in Sweden and his collaborators designed and synthesized a molecular light switch, which can control the activation of CIS trans or spiro part cyano Isomerization on the same photochromic skeleton In addition, three spiropyran structures with different photoresponse properties were reported for the first time, and their isomerization process was verified by UV and NMR Relevant achievements were published on J am Chem SOC (DOI: 10.1021 / JACS 8b09523) under the title of "shiningnew light on the spiropyran photoswitch: a photocage decisions between CIS − trans or spiro mercyanine isomerization" First of all, the author explored the process of CIS trans isomerization of trans partial cyan 1C trans MC and trans partial cyan 2me trans MC under light (scheme 1) Among them, 1c trans MC decomposes to 1mch under 254 nm light irradiation, and then it Protonates to 1mc under acid condition, 1mc isomerizes to 1sp under visible light irradiation and heating condition, and 1sp transforms to 1mc under ultraviolet light irradiation At the same time, trans-1c-trans-mc can also be converted into cis-mc under visible light irradiation, which can be converted into 1c trans-mc under 302 nm light and heating conditions In addition, trans-2me-trans-mc was transformed into cis-2me-cis-mc under visible light (source: J am Chem SOC.) then, the author studied the changes of UV absorption and emission spectra of 1C trans MC under light irradiation (Figure 1) The maximum absorption peak of 1C trans MC is 400 nm (black line) After irradiation at 405 nm, the original absorption peak at 400 nm disappeared, suggesting the completion of isomerization and the formation of light products (green lines) At room temperature, the author irradiated the product with 302 nm light for 38 minutes, and found that the absorption peak at 400 nm recovered to about 60% (blue line), which indicated that 1C trans MC could undergo reversible isomerization It was found that the absorption peak of 1C trans MC decreased at 400nm and a new absorption peak (red line) appeared at 541nm after 4 min of light irradiation It was concluded that the light irradiation at 254nm triggered the decomposition of 2-nitrobenzyl group in 1C trans MC and finally formed compound 1mc Furthermore, the UV irradiation of 1sp showed that the absorption spectrum of the isomers formed after irradiation was consistent with that of 1mc The above results of optical properties fully prove the structural transformation process of 1C trans MC under light irradiation (source: J am Chem SOC.) further, the author studied the transformation process of spirochrome structure by NMR The results show that the coupling constant of the two protons in the vinyl group of 1C trans MC is 16.8 Hz (Figure 2a), and the coupling constant changes to 12.8 Hz (Figure 2b) after irradiation at 405 nm, which is consistent with the assumed CIS trans isomer transformation In addition, spiropyran isomer and partial anthocyanin isomer can be observed by 1sp (Figure 2C) and its NMR spectrum after 30 minutes of 365 nm illumination (Figure 2D), so as to verify the transformation of spiropyran and partial anthocyanin structure Therefore, the structural transformation of spiropyran and epicanthus under light irradiation was further verified by NMR (source: J am Chem SOC.) in a word, the author designed a molecular light switch based on spiropyran, which shows three different light response properties: CIS trans isomerization under 405 nm light, decomposition of 2-nitrobenzyl group under 254 nm light, spiropyran blue isomerization under 365 nm light This kind of controlled activation isomerization is of great value in the construction of target bio related molecules and photochemical pharmacology.