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A Near‐Infrared Dye That Undergoes Multiple Interconversions through Acid–Base Equilibrium and Reversible Redox Processes
Author(s) -
Asai Kengo,
Fukazawa Aiko,
Yamaguchi Shigehiro
Publication year - 2017
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201702140
Subject(s) - redox , chemistry , protonation , photochemistry , fluorescence , absorption (acoustics) , electrochromism , radical ion , ion , base (topology) , infrared , inorganic chemistry , organic chemistry , materials science , electrode , mathematical analysis , physics , mathematics , quantum mechanics , composite material , optics
A near‐infrared (NIR) polymethine dye ( 1 ), consisting of a cyclohepta[1,2‐ b ;4,3‐ b′ ]dithiophene and two phenol moieties, was synthesized. This dye exhibited pH‐responsive changes in its photophysical properties due to a two‐step acid–base equilibrium that produced a protonated cation ( 1H + ) and an anion ( 1 − ). While 1H + showed an intense fluorescence in the red region of the visible spectrum, 1 − exhibited a strong absorption in the NIR region. The tropylium ion character in 1H + induces high p K a1 and p K a2 values for 1 . Moreover, a stable radical ( 1 . ) was prepared, which showed a NIR absorption band with a maximum at circa 1600 nm. The cyclic voltammogram of 1 . revealed a two‐step reversible redox process that produced 1 − and the cation 1 + , which is different from 1H + . These redox processes accompany drastic electrochromic changes in the vis–NIR region. Overall, 1 is susceptible to multiple interconversions between five forms, due to the multifaceted character of the cycloheptadithiophene skeleton.