Fluorescent Response Of H₂S To Compounds Based On Aggregation-induced Emission

As a gas signal molecule,H₂S can regulate a variety of physiological and pathological processes in mammals within a range of physiological concentrations.Therefore,the selective detection and imaging of H₂S in vivo have become a hot topic for researchers in recent years.It is important to find a suitable method to better understand its biological and pathological studies.The fluorescent probe is widely used in the detection of H₂S due to its high sensitivity,low noise and other advantages.On the one hand,the previous fluorescent probes exhibited small stokes shifts with different concentrations,and on the other hand,aggregate fluorescence quenching occurred during aggregation.The existence of these defects not only affects the detection process,but also greatly reduces the scope of application of the probe.The phenomenon of aggregation induced emission?AIE?proposed by Tang Benzhong's and colleagues solved this problem.Aggregation-induced emission?AIE?refers to a type of photophysical phenomenon in which fluorescence of a class of fluorescent chromophores luminesces is weak in a solution state or does not luminesce,whereas fluorescence in a solid state or in an aggregate state increases significantly.Compared with traditional fluorescent probe molecules,most of the fluorescence spectra of AIE molecules do not shift as their concentration changes,and molecules with AIE performance do not undergo fluorescence quenching in the aggregated state;finally,AIE fluorescent probes use a turn-on mechanism with relatively high sensitivity.Therefore,the synthesis of new AIE fluorescent probes and its use in chemical sensing and detection have important practical value.According to the above basis,this paper designed two AIE molecular systems for the detection of H₂S and studied their properties:a)Although fluorescein has been a traditional fluorescent dye till now,there are few reports on the dynamic equilibrium,luminescence mechanism,and aggregation behavior with the existence of H₂O.We focused on the fluorescence properties of three typical compounds,5-azidefluorescein?1?,5-aminofluorescein?2?and fluorescein?3?.Studies have found that:?i?H₂O can cleave the Ph-O bond of the spirolactam ring and the process is irreversible even by heating and irradiation;?ii?The azide group does not quench the fluorescence of the fluorescein system,5-azide fluorescein showed strong green fluorescence in 100%water,and the fluorescence of this system was due to the effect of molecular aggregation-induced emission?AIE?;?iii?Theoretical calculations?DFT?verified the theoretical basis for the fluorescence emission of 1_o,2_o and 3_o?open-loop form?and 1_c?closed form?,and optimize the structure and transition characteristics;?iv?Based on this,the reaction between 1 and H₂S and NO was studied in turn.First,after reacting with H₂S,the azide group in 1 is reduced to amino group,the fluorescence at 515nm is reduced by 11 times,and the detection limit is about 2.6?M;second,after the deamination reaction with NO,the fluorescence intensity at 526 nm increased 5-fold,and the detection limit was 0.12?M;?v?Probe 1 can be applied to fluorescence imaging experiments of PC12 cells sequentially added with H₂S and NO,and we further investigated the cellular fluorescence imaging of NO produced by cells induced by lipopolysaccharide LPS and probe 2.b)Two cyano-based fluorescent chemical probes,Cya-NO₂?1?and Cya-N₃?2?,were studied,and selectivity and sensitivity of hydrogen sulfide?H₂S?were tested.Cya-NO₂?1?was synthesized by knoerenage condensation of 4-formyltriphenylamine and4-nitrobenzeneacetonitrile in a piperidine/ethanol solution.The product of Cya-NH₂?3?is then reduced by stannous chloride,followed by azide formation using NaN₃ to form Cya-N₃?2?.Both of these probes showed aggregation-induced emission?AIE?,which caused a large stokes shift in the red region and a rapid response to H₂S with greater colorimetric and ratiometric fluorescence changes.After 10 equivalent of H₂S were added to probe 1,the fluorescence intensity at 637 nm enhanced 13-fold,and the detection limit was approximately 6.87?M.While probe 2 enhanced 8-fold at 535 nm after adding 10equivalents of H₂S,and the detection limit is about 0.52?M.Finally,probes 1 and 2 were successfully used in the fluorescence imaging in hela cells.In conclusion,several of our probes for the detection of H₂S have good AIE characteristics.After the electron-withdrawing azide group or nitro group is reduced to an electron-donating amino group,the AIE characteristics are changed to achieve a response to H₂S.