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Switchable Mesomeric Betaines Derived from Pyridinium‐Phenolates and Bis(thienyl)ethane
Author(s) -
Nagorny Sven,
Lederle Felix,
Udachin Viktor,
Weingartz Thea,
Hübner Eike G.,
Dahle Sebastian,
MausFriedrichs Wolfgang,
Adams Jörg,
Schmidt Andreas
Publication year - 2021
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.202100279
Subject(s) - chemistry , pyridinium , substituent , anisole , chromophore , bathochromic shift , conjugated system , medicinal chemistry , pyridine , polar effect , photochemistry , stereochemistry , fluorescence , organic chemistry , catalysis , physics , polymer , quantum mechanics
Syntheses of push–pull substituted non‐symmetric bis(thienyl)ethenes (BTEs) possessing a central perfluorocyclopentene core are described. The substituent effects of anisole, phenole, and phenolate as well as pyridine, pyridinium, and N ‐methylpyridinium substituents, joined through their 3‐ or 4‐positions to the central BTE core, respectively, cover the range from very strongly electron‐donating [σ(4‐phenolate)=−1.00] to extremely strongly electron‐withdrawing [σ(pyridinium‐4‐yl)=+2.57] in the title mesomeric betaines. The different isomers possessing 4‐yl/4‐yl, 4‐yl/3‐yl and 3‐yl/3‐yl substituents represent different combinations of conjugated and cross‐conjugated partial structures and cause different spectroscopic properties. In addition, through‐space conjugation between the 2‐ and 2′‐position of the thiophenes can be observed which circumvents the charge‐separation of through‐bond cross‐conjugation. The BTE possessing the push–pull chromophore consisting of 3‐anisole and 4‐pyridinium substituents ( 24 ) displays the best extinction coefficients within the series of compounds described here (ϵ=33.8/15.7 L/mol ⋅ cm), while the mesomeric betaine possessing an N ‐methylpyridinium‐4‐yl and a 4‐phenolate substituent ( 29 ) displays considerable bathochromic shifts to λ max =724 nm in its closed form.