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Synthesis and Optical Properties of Push–Push–Pull Chromophores Based on Imidazo[5,1,2‐ cd ]indolizines and Naphtho[1 ′ ,2 ′ :4,5]imidazo[1,2‐ a ]pyridines
Author(s) -
Maitra Ratnava,
Chen JieHong,
Hu ChingHan,
Lee Hon Man
Publication year - 2017
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.201701109
Subject(s) - chemistry , diphenylacetylene , chromophore , photochemistry , intramolecular force , pyridine , quantum yield , fluorescence , acceptor , palladium , quenching (fluorescence) , biphenyl , catalysis , medicinal chemistry , stereochemistry , organic chemistry , physics , quantum mechanics , condensed matter physics
Four series of new push–push–pull chromophores based on two types of heterocyclic cores, namely imidazo[5,1,2‐ cd ]indolizines and naphtho[1 ′ ,2 ′ :4,5]imidazo[1,2‐ a ]pyridines, and two types of linear π spacers, namely diphenylacetylene and biphenyl, were prepared. The two isomeric heterocyclic compounds were prepared by palladium‐catalyzed double C–H functionalization reactions. Further palladium‐catalyzed C–C coupling reactions allow the construction of diphenylacetylene and biphenyl spacers on the chromophores. Different electron‐donors including NMe 2 , NPh 2 , and OMe and CN acceptors were incorporated into the chromophores. The corresponding donor‐ and acceptor‐free compounds were also prepared for comparative studies. In the case of chromophores with strong NMe 2 or NPh 2 donors, a strong intramolecular charge‐transfer (ICT) process occurs leading to fluorescence emission quenching in polar solvents. The use of a slightly weaker OMe donor together with the naphtho[1 ′ ,2 ′ :4,5]imidazo[1,2‐ a ]pyridine core allows to obtain an intense blue fluorescence with high quantum yield of up to 0.825. DFT and TD‐DFT calculations offer satisfactory explanations to the observed photophysical data.