title: A new series of fluorescent indicators for super acids.
abstract: The photophysical properties of fluorescent Hammett acidity indicator derived from 3,4,5,6-tetrahydrobis(pyrido[3,2-g]indolo)[2,3-a:3',2'-j]acridine (1a), 6-bis(pyrido[3,2-g]indol-2'-yl)pyridine (1b) and their analogues have been investigated in sulfuric acid solutions by means of absorption, fluorimetry, relaxation dynamics and computational approach. These new indicators undergo a reversible protonation process in the Hammett acidity range of H0 < 0, accompanied by a drastic increase of the bright blue-green (1a) or yellow (1b) fluorescence intensity upon increasing the acidity. For 1a in H2 SO4 , the emission yield increases as large as 200 folds from pH = -0.41 to the Hammett acidity range of -5.17, the results of which are rationalized by a much increase of the steric hindrance upon third protonation toward the central pyridinic site, together with their accompanied changes of electronic configuration from charge transfer to a delocalized ππ* character in the lowest lying excited state. The combination of 1a and 1b renders a wide and linear range of H0 measurement from -1.2 to -5.1 detected by highly intensive fluorescence.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei, Taiwan.
authors.forename: I-Chih
authors.initials: IC
authors.lastname: Shih
authors.forename: Yu-Shan
authors.initials: YS
authors.lastname: Yeh
authors.forename: I-Che
authors.initials: IC
authors.lastname: Wu
authors.forename: You-Hua
authors.initials: YH
authors.lastname: Chen
authors.forename: Jiun-Yi
authors.initials: JY
authors.lastname: Shen
authors.forename: Yi-An
authors.initials: YA
authors.lastname: Chen
authors.forename: Mei-Lin
authors.initials: ML
authors.lastname: Ho
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
mesh_terms: D000143:Acids / Q000032:analysis*; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D011522:Protons; D011789:Quantum Theory; D013464:Sulfuric Acids / Q000032:analysis / Q000737:chemistry
chemical_list: D000143:Acids; D005456:Fluorescent Dyes; D011522:Protons; D013464:Sulfuric Acids; C033158:sulfuric acid