Research On The Bifuctional Fluorescent Probes Based On Triarylborane Derivatives

As one of the most toxic heavy metal ions, mercury ions have caused great harm to the environment and human health; F- is widely distributed in nature in the form of fluoride, playing important roles in ecological environment and human health; additionally, pH is an important indicator of the human health, and plays a great role in various metabolic processes in cells. Thus, establishing an effective method for detecting Hg2+, F- and pH is of great importance. Compared to the traditional methods of ions detection, such as atomic absorption, high performance liquid chromatography and electrochemical analysis, fluorescence detection has the advantages of high sensitivity, high selectivity, and simple, getting more and more attention. Although, lots of fluorescent probes for Hg2+, F- and pH, but the examples for detection of two ions simultaneously are still quite limited.In a recent study, our group has designed and synthesized BN, 2-dimesitylboryl-2’-(N,N-dimethylamino)biphenyl, the complexation of F- and the tri-coordinate boron center could lead to a long blue shift (165 nm), enabling the ratiometric fluorescence detection of F-. It is notable that the para-position of the amino group is very reactive towards electrophilic substitution, so we expect to introduce groups which could detect other ions into BN to obtain bifunctional fluorescent probes for detecting F- and other ions simultaneously. Based on this design concept, we carried out the following two works:Firstly, we introduced thioacetal group which could response to Hg2+ into the para-position of the amino group in BN by formylation and condensation reaction to synthesized BN-S, used as a bifunctional fluorescence probe for detecting Hg2+ and F-BN-S shows intramolecular charge transfer, and displays intense fluorescence not only in organic solution but also in water in form of nano-aggregates. The addition of Hg2+leads to the deprotection of thioacetal to obtain an aldehyde group, resulting in a blue shift in the maximum emission wavelength with a color change from greenish yellow to green. And the addition of F- would disrupt the pπ-π* conjugation, leading to a blue shift along with a color change from yellow to blue. In this way, BN-S behaves as a promising ratiometric bifunctional fluorescence probe to detect Hg2+ and F-simultaneously. Additionally, the detection of Hg2+ is performable in an aqueous medium using its nano-aggregates.Secondly, we introduced pyridine which could detect H+ into the para-position of the amino group in BN by the bromination and Suzuki reaction to get the fluorescent compounds 1,2,3. for the fluorescent detection of both Hg2+ and H+.These findings could provide a theoretical basis for the depth study of the optical properties of BN and the further design of bifunctional fluorescent probes utilizing this skeleton.