Organic "turn on" fluorescent molecular switch based on imidazole dimer

Since the Dutch invented the first optical microscope in the world at the end of the 16th century, the microscope has been continuously used and improved as a tool to observe the internal microstructure of cells However, optical microscopy only uses the natural differences in optical properties of different microstructures of biological samples to distinguish them, which results in some cell structures can not be observed After Stokes observed the fluorescence phenomenon in the 19th century, the fluorescence microscope, which uses the exogenous fluorescence probe with molecular specificity to label the intracellular molecules, has been widely used in the study of the living intracellular life phenomena due to its advantages of low damage, high specificity, high sensitivity and real-time dynamic imaging With the development of fluorescence microscopy, the fluorescence imaging based on single molecule positioning technology has reached the resolution of nanometer scale, but these imaging technologies also have higher and higher requirements for fluorescence molecules, especially in the field of super-resolution microscopy, such as fluorescence super-resolution microscopy based on Reversible Saturated light transfer process (resolft) and random optical reconstruction microscopy（ Storm) and so on require fluorescent molecules to be able to carry out light / dark state conversion Fig 1 Molecular structure and mutual transformation of fluorescent molecular switches 1 and 2 (photo source: J am Chem SOC.) recently, Professor Jiro Abe's research team at Aoyama University in Japan reported a kind of molecular switch with "turn on" performance (Fig 1) They used photochromic imazole dimer (BN IMD ）It combines with naphthalimide derivatives to form fluorescent molecules with fluorescence energy resonance transfer (FRET) This molecule appears orange at the initial stage, but due to the presence of fret, it does not emit fluorescence When it isomerizes under light conditions, its color will change to yellow and emit strong fluorescence This achievement was published in the Journal of the American Chemical Society (DOI: 10.1021 / JACS 9b01870) under the title of "turn on mode fluorescence switch by using negative photochromicimidazole dimer" Fig 2 The synthesis path of molecule 1 (photo source: J am Chem SOC.) probe is shown in Fig 2 The linkage group 1a is obtained by demethylation of anisidine It will react with two naphthalimide containing bromine to obtain one branch 1g of fluorescence molecule, while the other branch of fluorescence molecule is anisidine The skeleton structure of fluorescent molecule is 2-naphthol, which reacts with n-butyl lithium and DMF to obtain the intermediate 1b containing aldehyde group Then 1b reacted with anisidyl and branched chain 1g respectively to obtain the precursor of the target fluorescent molecule for 1h, and the final 1H was obtained by isomerization under the condition of avoiding light The structure and synthesis of 2 are similar to 1, but the distance between naphthalimide and anisidine is reduced Fig 3 A) the transformation of 1 and 2 at different temperatures; b) the absorption, fluorescence and emission spectra of 1 and 2 (photo source: J am Chem SOC.) after obtaining the target molecule, the author studied its isomerization reaction under light and heating conditions (Fig 3) The results showed that the UV absorption of 1-O and 2-O decreased at 500 nm, while the UV absorption of naphthalimide at 400 nm did not change After stopping the irradiation, 1-y and 2-y were gradually converted into 1-O and 2-O, and the conversion process was controlled by thermal mechanics The half lives of 1-y and 2-y at 298 K were 110 s and 48 s respectively The photophysical properties of 1-O and 2-O were studied after the isomerization of 1 and 2 were confirmed The results showed that under the same conditions, the fluorescence signals of 1-O and 2-O could hardly be detected, while the fluorescence emission of 1-y and 2-y was obvious at 500 nm The fluorescence quantum yields of the four molecules were measured 0.01, 0.75, 0.01 and 0.71 (1-O, 1-y, 2-O and 2-y), indicating that the intramolecular FRET was indeed inhibited after isomerization Highlight: the author developed a kind of "turn on" fluorescent molecule, which can realize the transition from dark state to light state by light Full text author: Katsuya Mutoh, NANAE Miyashita, Kaho Arai and Jiro Abe.