| In recent years,as the sustainable development of biosciences,fluorescence analysis technology has received extensive attention from many scientists,due to its high signal-to-noise ratio,high sensitivity,convenience for handling,and environmental friendliness.Therefore,Fluorescent compounds that can provide useful information from biological responses through specific interactions are of paramount importance for medicine,molecular and cellular biology,chemistry,chemical biology,and other interdisciplinary sciences.benzothiadiazole(BTD)fluorescent dyes have the following advantages,such as:(1)efficient and stable fluorophores,even in excited states.(2)Strong electron-withdrawing capacity.(3)Highly polarized properties,normally affording well-ordered crystal structure.(4)Display large Stokes shifts.(5)High stability under long irradiation.(6)Typically display bright emission during cellular experiments time periods.(7)High signal-to-noise ratio.(8)Efficiently transposing the cellular membrane.(9)It is typically excited in the visible-light region and exhibits high quality imaging.In biological monitoring,fluorescent probes and other fields have shown excellent physical and chemical properties.It is great significance to design and synthesize benzothiadiazole(BTD)-based fluorescent dyes with red light emission.Firstly,considering of the relationship of molecular properties-structure on the luminescent,we have designed and synthesized a series of BTD-based conjugated molecules C1-C4 with push-pull structures,in which vinyl group as conjugated bridges,N,N-diethylaniline or N-phenylethanolamine as an electron donor and benzothiadiazole group or bromobenzothiadiazole group as electron acceptors respectively.Strong fluorescence quantum yield(up to 88%)and large Stokes shift(up to 150 nm)of the BTD-based fluorescent had been found by UV-vis absorption spectra and emission spectra.And the relationship of their structure and optical properties of the fluorecent has also been discussed.Through the study of the spectral properties of four molecules,C1 and C2 molecules show selective response to toxic vapor of toluene.The fluorescence quantum yield in toluene were as high as 88.2%.Moreover,all solid state of C1,C2,and C3 show different extent of emission after excited by visible light.The solid fluorescence quantum yield of C3 was 24.3%.The Stokes shifts of the four molecules are all greater than 100 nm,which has a certain application prospect in cell imaging.On the other hand,it is also meaningful to investigate the fluorescent probe for low pH value,since the living environment of many microbes was under strongly acidic condition.According to the molecular structure of C1-C4 and its performance in detecting the low pH value of the solution,we have designed and synthesized a molecule C5 with a better pH fluorescence response.N-phenylethanolamine is used as electron donor for this molecule,vinyl is used as conjugated bridge,benzothiadiazole formaldehyde is electron acceptor.The experimental results shows that C5 presents a large Stokes shift(>100 nm)and excellent specificity and light stability.The titration results shows that the fluorescence intensity gradually decreases with the increased pH from 0 to 3.04 of pH value.The pKa of the C5 probe is 1.56.Therefore,it’s reasonable to conduct that C5 molecules exhibit a promising potential as pH probes under extremely acidic conditions. |
