Henary Maged M, Wu Yonggang, Cody John, Sumalekshmy S, Li Jing, Mandal Subrata, Fahrni Christoph J
School of Chemistry and Biochemistry and Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, USA.
J Org Chem. 2007 Jun 22;72(13):4784-97. doi: 10.1021/jo070433l. Epub 2007 May 25.
A series of water-soluble 2-(2'-arylsulfonamidophenyl)benzimidazole derivatives containing electron-donating and accepting groups attached to various positions of the fluorophore pi-system has been synthesized and characterized in aqueous solution at 0.1 M ionic strength. The measured pK(a)'s for deprotonation of the sulfonamide group of monosubstituted derivatives range between 6.75 and 9.33 and follow closely Hammett's free energy relationship. In neutral aqueous buffer, all compounds undergo efficient excited-state intramolecular proton transfer (ESIPT) to yield a strongly Stokes-shifted fluorescence emission from the phototautomer. Upon deprotonation of the sulfonamide nitrogen at high pH, ESIPT is interrupted to yield a new, blue-shifted emission band. The peak absorption and emission energies were strongly influenced by the nature of the substituents and their attachment positions on the fluorophore pi-system. The fluorescence quantum yield of the ESIPT tautomers revealed a significant correlation with the observed Stokes shifts. The study provides valuable information regarding substituent effects on the photophysical properties of this class of ESIPT fluorophores in an aqueous environment and may offer guidelines for designing emission ratiometric pH or metal-cation sensors for biological applications.
一系列含有供电子和吸电子基团的水溶性2-(2'-芳基磺酰胺基苯基)苯并咪唑衍生物已被合成，并在0.1 M离子强度的水溶液中进行了表征。单取代衍生物磺酰胺基团去质子化的实测pK(a)值在6.75至9.33之间，与哈米特自由能关系密切相关。在中性水性缓冲液中，所有化合物都经历高效的激发态分子内质子转移(ESIPT)，从光互变异构体产生强烈的斯托克斯位移荧光发射。在高pH值下磺酰胺氮去质子化后，ESIPT被中断，产生一个新的蓝移发射带。峰值吸收和发射能量受到取代基的性质及其在荧光团π体系上的连接位置的强烈影响。ESIPT互变异构体的荧光量子产率与观察到的斯托克斯位移有显著相关性。该研究提供了关于取代基对这类ESIPT荧光团在水性环境中的光物理性质影响的有价值信息，并可能为设计用于生物应用的发射比率pH或金属阳离子传感器提供指导。
