Preparation Of Dihalofluorescein And Fluorescent Film And Their Properties

Fluorescein as a fluorescent probe is extensively utilized in life science and environmental detection due to its strong ability of fluorescence emission, excitation and emission wavelength in the visible range as well as innoxiousness. However, it is easy to undergo photobleaching process during use and the fluorescent intensity is low in acid conditions. These drawbacks limit its further application. On one hand, many researches have been done on synthesizing new fluorescein derivatives with excellent proerties by structure modification, but the effect of modifier to photophysical properties of fluorescein still remains unknown. On the other hand, homogeneous fluorescent sensors are widely applied in identification of metal ions, anions and neutral molecules owing to their high sensitivity and favorable selectivity, but they could be hardly made into devices, for its disposability and contamination to the analyte. In contrast to homogeneous fluorescent sensors, film sensors could overcome these disadvantages and have aroused researchers’ attention.Firstly,2’,7’-difluorofluorescein (DFF),2’,7’-dichlorofluorescein (DCF) and2’,7’-dibromo fluorescein(DBF) were synthesized by Friedel-Crafts acylation/cyclodehydration reaction and then characterized. The effects on photophysical properties of fluorescein with different halogen substitution were studied. The result revealed that the lifetime of DFF and DCF were remarkably increased, and their properties of photobleaching resistance were significantly enhanced. Meanwhile their fluorescence quantum yield was higher, while the thermodynamic pKa value was lower. However, the increase in fluorescent property of DBF was restricted due to the heavy atom effect of bromine. In addition, the results indicated that dihalofluorescein were sensitive to concentration、solvent、pH value. They reached the maximum fluorescent intensity at1×10-5mol/L when dissolved in0.1mol/L NaOH solution. Compared with aprotic solvent, they had longer emission wavelength and higher fluorescent intensity in protic solvent. Their fluorescent intensity and absorption wavelength were also sensitive to pH value, which make them excellent candidates for polarity probe and pH probe.Moreover, influencing factors of preparing dye doped silica film under acid or base condition by sol-gel method were investigated. When mixing TEOS, EtOH and H2O in molar ratio of1:4.8:4, and pH was adjusted to4-5in acid or8-9in base, the stable dye doped silica film was successfully prepared. The fluorescent properties of dye doped silica film were intensively examined. It was found that the fluorescent properties of fluoresceins in sol are similar to those in solution. To address the problem of film crack, the hybrid silica film was fabricated using3-glycidoxypropyltrimethoxysilane(GPTMS) as a modifier by sol-gel method. The result indicated that when GPTMS was added, the absorption wavelength of dye in film was bathochromic shift and the resultant film was free crack. Meanwhile, the thermal stability of film was improved by thermogravimetric analysis.