Circularly polarized luminescence of non chiral cyanine dyes

Circular polarized luminescence (CPL) is a kind of chirality phenomenon, and its generation is not complicated As we all know, a plane polarized light can be divided into two circularly polarized light with the same intensity, spiraling forward and opposite direction, i.e right-handed polarized light and left-handed polarized light When the light passes through some special medium or due to the reason of the luminescent body itself, it can lead to the imbalance of the amplitude and speed between the left-handed and right-handed polarized light, which leads to the elliptical polarized light On the basis of this, some materials with chiral characteristics can emit circularly polarized light with unequal left and right rotation, which is called circularly polarized luminescence, or CPL phenomenon Due to the potential application value of circularly polarized light-emitting materials in biosensor, 3D optical display, information storage, etc., it has become a research hotspot to explore and develop materials with circularly polarized light-emitting properties Most of the traditional CPL materials have high fluorescence emission in solution, but its ACQ effect largely limits the application of such materials Since Tang benzhong discovered the AIE effect in 2001, the aggregation induced circular polarization luminescence (ai-cpl) material with AIE activity has gradually become one of the research focuses of CPL materials Figure 1 Structure of the probe (photo source: J am Chem SOC.) recently, researcher Ding Baoquan, National Center for nanoscience, and Associate Professor Peng Qian, Institute of chemistry, Chinese Academy of Sciences Based on the theory of AIE, which is to limit the free rotation of some groups in the molecule and enhance their fluorescence effect, they successfully restricted the free rotation of groups on carbazole dyes through their chiral DNA This strategy not only greatly increases the fluorescence intensity of the binding between DNA molecules and the groups on carbazole dyes, but also promotes the chiral transfer of DNA molecules to the dye molecules, making the dye molecules have CPL characteristics This achievement was published in the Journal of the American Chemical Society (DOI: 10.1021 / JACS 9b03305) under the title of "circularly polarized luminescenceof active cyanine molecules assembled on DNA templates" Fig 2 A) schematic diagram of probe binding with single and double stranded DNA; b) UV absorption spectrum before and after probe binding with single and double stranded DNA; c) fluorescence emission spectrum before and after probe binding with single and double stranded DNA; d) CD spectrum before and after probe binding with single and double stranded DNA; E) CPL spectrum after probe binding with single and double stranded DNA; F ）CPL map of the probe combined with double stranded DNA with temperature change (photo source: J am Chem SOC.) the fluorescent molecule is a cyanine dye derivative based on carbazole, and its synthesis is not complicated After alkylation of nitrogen atom on carbazole and reaction with NBS, the derivative of 3,6-dibromocarbonazole can be obtained, and then 3 can be obtained through formylation and substitution reaction, The corresponding probes can be obtained by Knoevenagel condensation of 6-dialdehyde carbazole derivatives and aldehyde derivatives with n-methyl-4-methylpyridine After obtaining the probe, the author then tested the changes of absorption and emission spectra before and after the binding of the probe and DNA molecule (Fig 2B, 2C) The results show that both single strand DNA (ssDNA) and double strand DNA (dsDNA) can combine with the probe and enhance its fluorescence (Fig 2C), but the interaction between dsDNA and the probe is stronger, which can better limit the free rotation of the probe, so it can enhance the fluorescence intensity of the probe more significantly Through the characterization of circular dichroism (CD) and CPL, the author found that the chirality of DNA molecules can be transferred to dye molecules after binding with DNA molecules, so that dye molecules without chirality can have CPL effect in the range of 480-750 nm (Fig 2e) In addition, the author also found that after the DNA molecule with the enantiomeric relationship is combined with the probe, its enantiomeric relationship will also be transferred to the probe, and the combination of DNA molecule and the probe is not unchangeable By changing the temperature of the system, the author found that the assembly of DNA and the probe can be regulated by temperature (Fig 2f) Highlights of the paper: the author reports a preparation strategy of CPL materials based on supramolecular assembly behavior, which provides a new way for the design of new chiral luminescent materials Full text author: Qiao Jiang, Xuehui Xu, Ping An Yin, Kai Ma, Yonggang Zhen, Pengfei Duan, Qian Peng *, Wei Qiang Chen and Baoquan Ding *.