Abstract
Novel triene merocyanines, i.e. 1-styryleth-2-enylidene and 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are obtained in good to excellent yields in a consecutive three-component insertion Sonogashira coupling–addition sequence. The selectivity of either series is remarkable and has its origin in the stepwise character of the terminal addition step as shown by extensive computations on the DFT level. All merocyanines display intense absorption bands in solution and the film spectra indicate J-aggregation. While 1-styryleth-2-enylideneindolones show an intense deep red emission in films, 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are essentially nonemissive in films or in the solid state. TD-DFT computations rationalize the charge-transfer nature of the characteristic broad long-wavelength absorptions bands.
Highlights
Functional organic materials [1], such as chromophores, fluorophores, and electrophores, constitute the active components in molecular electronics [2], photonics [3], and bioanalytics [4,5,6]
After the coupling of the N-methyl-substituted alkynoyl o-iodoanilides 5a and terminal arylalkynes 6 at room temperature under Sonogashira conditions forming ynylideneindolones as intermediates [30,31,32], which were not isolated, an ethanolic solution of Fischer’s base (7) was added and reacted at reflux temperature to give 1-styryleth-2-enylideneindolones 8 in good to excellent yields as violet solids with a metallic luster (Scheme 1, Table 1)
While the phenyl substituents on the triene chromophore largely contribute to shorter wavelength absorption bands, the tosyl moiety does not display any coefficient density in the FMOs and, qualifies as a favorable electronic innocent bridge for ligating other chromophores to this novel class of merocyanines
Summary
Functional organic materials [1], such as chromophores, fluorophores, and electrophores, constitute the active components in molecular electronics [2], photonics [3], and bioanalytics [4,5,6]. After the coupling of the N-methyl-substituted alkynoyl o-iodoanilides 5a and terminal arylalkynes 6 at room temperature under Sonogashira conditions forming ynylideneindolones as intermediates (the reaction was monitored by TLC to ensure complete conversion) [30,31,32], which were not isolated, an ethanolic solution of Fischer’s base (7) was added and reacted at reflux temperature to give 1-styryleth-2-enylideneindolones 8 in good to excellent yields as violet solids with a metallic luster (Scheme 1, Table 1).
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