Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192-0101, USA.
J Phys Chem A. 2011 Jul 14;115(27):7912-20. doi: 10.1021/jp201209k. Epub 2011 Jun 16.
4-(2-Methylbutyl)aminodipicolinic acid (H(2)MEBADPA) has been synthesized and fully characterized in terms of aqueous phase protonation constants (pK(a)'s) and photophysical measurements. The pK(a)'s were determined by spectrophotometric titrations, utilizing a fully sealed titration system. Photophysical measurements consisted of room temperature fluorescence and frozen solution phosphorescence as well as quantum yield determinations at various pH, which showed that only fully deprotonated MEBADPA(2-) is appreciably emissive. The fluorescence of MEBADPA(2-) has been determined to be quenched by hydroxide and methoxide anions, most likely through base-catalyzed excited-state tautomerism or proton transfer. This quenching phenomenon has been quantitatively explored through steady-state and time-resolved fluorescence measurements. Utilizing the determined pK(a)s and quenching constants, the fluorescent intensity of MEBADPA(2-) has been successfully modeled as a function of pH.
4-(2-甲基丁基)氨基二吡啶酸（H（2）MEBADPA）已被合成，并在水相质子化常数（pK（a）'）和光物理测量方面进行了全面表征。pK（a）'通过分光光度滴定法确定，利用完全密封的滴定系统。光物理测量包括室温荧光和冷冻溶液磷光以及在不同 pH 值下的量子产率测定，结果表明只有完全去质子化的 MEBADPA（2-）才有明显的发光性。已经确定 MEBADPA（2-）的荧光被氢氧化物和甲氧基阴离子猝灭，很可能是通过碱催化的激发态互变异构或质子转移。通过稳态和时间分辨荧光测量定量研究了这种猝灭现象。利用确定的 pK（a）和猝灭常数，成功地将 MEBADPA（2-）的荧光强度建模为 pH 的函数。
