Study On The Deconjugation Of Benzoindole Trimethine Cyanines As Well As The Photophysical Properties And Applications Of Their Dderivatives

Modification of aromatic ring/aromatic heterocycle,heterocyclic nitrogen or conjugated methine chain in cyanine dyes can greatly improve their properties and expand their application ranges,which have attracted extensive attention.In particular,the introduction of substituents on the methine chain and the construction of a novel D-π-A conjugated structure after the deconjugation of methine chain have become a research hotspot.In this paper,the studies on modification and deconjugation of the methine chains of benzoindole trimethine cyanines were carried out,and novel stimulus-responsive spirocyanine dyes and cyanine-based conjugated derivatives were synthesized.The structures,photophysical properties and applications of the resulting products were investigated.This paper mainly includes the following contents:1.The modification of cyanine methine chain and the applications of the resulting products,as well as the deconjugation of cyanine methine chain were reviewed.2.The deconjugation reaction between benzoindole trimethine cyanines and nitrosating reagents was studied,and three new spirocyclic cyanine dyes（2a-c）were synthesized from this.Three new cyanine-based conjugated derivatives（2ab-cb）were prepared by the formylation of the methine chain of benzoindole trimethine cyanines,followed by reduction with sodium borohydride.The products were characterized by UV-Vis,¹H NMR,¹³C{1H}NMR and HRMS.The single crystals of spirocyanine and related compounds were cultured,and the crystal test and crystal analysis were carried out.3.The photostability of dyes 2a-c and 2ab-cb in ethanol were investigated.After irradiation with iodine tungsten lamp for 100 min,the absorbance of 2a-c and 2ab-cb were all decreased in varying degrees,but less than 6-10%,indicating that these dyes had good photostability.4.The UV-Vis absorption spectra of 2a-c and 2ab-cb in different solvents were determined.The maximum absorption wavelength(λ_max)and molar extinction coefficient（ε）of 2a-c in DMSO,Me OH,Et OH and pyridine were in the range of 306-308 nm and1.62×10⁴-4.26×10⁴L·M^-1·cm^-1,respectively,and in PBS and acetic acid,theλ_maxandεof2a-c were in the range of 380-386 nm and 0.71×10⁴-1.96×10⁴L·M^-1·cm^-1,respectively,which showed strong solvation effect.Theλ_maxandεof 2ab-cb were 443-455 nm and2.47×10⁴-4.70×10⁴L·M^-1·cm^-1,respectively,showing a small solvation effect.5.The pH sensing performance of spirocyanine dye 2a was investigated.From pH 7.0 to1.0,the absorption intensity at 308 nm decreased gradually,while that at 380 nm increased gradually.The color of the solution also changed from colorless to orange yellow.When the pH was between 8.0 and 13.5,the main absorption was at 308 nm,and there was no absorption above 350 nm.In the range of pH 1-4,the absorbance of 2a at 310 nm showed a good linear relationship with pH,y=0.2113+0.0173x,R²=0.9938.2a could be used as a lower pH sensor.6.The temperature sensing performance of spirocyanine dye 2a was investigated.At40℃,the absorption of 2a in buffer（pH=2）-Me OH（3:2,v/v）mixture gradually decreased at 380 nm and increased at 510 nm with time.The color of the solution also changed from orange yellow to orange red.And a clear isosbestic point appeared at 448 nm,indicating that 2a took place opening-ring reaction.From 25℃to 45℃,the absorption intensity of spiro（SP）decreased gradually,and that of opening-ring product（MC）increased gradually,and the solution color was orange-yellow but changed to light pink and then to orange red.Log K(A_MC/A_SP)had a good linear relationship with temperature between 25 and 45℃,demonstrating that the temperature of the liquid environment could roughly be estimated using 2a.According to the crystal structure of spirocyanine 2a and its opening-ring product 2aa,the mechanism of the opening-ring reaction of 2a was speculated,and the thermochromic mechanism of 2a in acidic condition was proposed.