Study On The Synthetic Methods Of Methine-substituted Benzoindole Trimethincyanines And Their Photophysical Properties

The methine-substituted trimethinecyanines have immense application value in the field of biomedicine and optical materials.However,they still relies on inefficient multistep reactions requiring harsh reaction conditions with poor substrate scope and yields.Besides,some substituents can not be introduced to the methine chain by the reported ways.Therefore,it is an urgent task to develop a simple and effective synthetic method to prepare methine-substituted trimethine cyanine with specific properties and functions.In this paper,we explored the electrophilic substitution reactions between the methine chain on symmetrical benzoindole trimethinecyanines and many electrophiles,and investigated new methods to synthesize methine-substituted benzoindole trimethinecyanine in one step.Then,we studied the spectral properties,stability and water solubility of the synthesized products and summarized the relationship between molecular structure and properties.The main contents of the paper are the following:1.The synthesis,properties and applications of methine-substituted trimethinecyanines have been reviewed in recent years.2.The reactions and mechanisms between the methine on benzoindole trimethinecyanine and many electrophiles were investigated.And twenty-four kinds of novel methine-substituted benzoindole trimethinecyanine were prepared by directly introducing substituents such as halogen,nitro,alkyl,formyl or methionyl on the methine of benzoindole trimethinecyanine in one-step.3.The UV-Vis absorption spectra of various dyes in four different solvents were investigated.Compared with the parent dyes,the maximum absorption of the dyes which were substituted by halogen,alkyl or methionyl on their methine had a red shift about 3-16 nm,and the dyes which were substituted by nitro or formyl on their methine had a blue shift about 70-120 nm.Besides,the molar extinction coefficient of all kinds of dyes is above 104L·mol-1cm-1.Meanwhile,the introduction of substituents on the methine could increased the steric hindrance of dye molecules and inhibited the intermolecular aggregation,thus,the aggregation peaks of methine-substituted dyes in different solvents are not obvious or even disappear.4.The effect of different substituents on the photostabilization of the methine-substituted benzoindole trimethincyanines was investigated,and the results were as follows: After illumination for 60 min,the absorbance of the parent dye was reduced by about 90%,and the absorbance of the halogenated and alkylated dyes on the methine was reduced by about 25% and 55%,respectively.While the absorbance of nitrified and formylated dyes on methine was almost no change.From the above,the introduction of the substituents on the methine could improve the photostability of the methine-substituted benzoindole trimethincyanines,in which nitro or formyl-substituted dyes basically were not photodegraded.5.The effect of different substituents on the solubility of the methine-substituted benzoindole trimethincyanines in water was investigated and the results were as follows: The introduction of halogen or alkyl on methine could increased the solubility of the dyes indistinctly.While introducing nitro or formyl to methine could increase the solubility of the dyes greatly,and their solubility were 4-5 times that of parent dye.From the above,introducing substituents to methine could increase the solubility of the methine-substituted benzoindole trimethincyanines,and nitro or formyl-substituted benzoindole trimethinecyanines had a lager solubility in aqueous solution.