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A New Series of Fluorescent Indicators for Super Acids
Author(s) -
Shih IChih,
Yeh YuShan,
Wu IChe,
Chen YouHua,
Shen JiunYi,
Chen YiAn,
Ho MeiLin,
Chou PiTai
Publication year - 2014
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12326
Subject(s) - protonation , chemistry , fluorescence , steric effects , delocalized electron , acridine , photochemistry , excited state , absorption (acoustics) , pyridine , sulfuric acid , relaxation (psychology) , quantum yield , stereochemistry , inorganic chemistry , medicinal chemistry , organic chemistry , ion , social psychology , psychology , physics , quantum mechanics , nuclear physics , acoustics
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 H 0 < 0, accompanied by a drastic increase of the bright blue‐green (1a) or yellow (1b) fluorescence intensity upon increasing the acidity. For 1a in H 2 SO 4 , 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 H 0 measurement from −1.2 to −5.1 detected by highly intensive fluorescence.