The formation of chromophores by multi‐component reactions is a synthetically favorable and highly practical chromogenic concept for exploring functional and structural space of solid state and aggregation induced emission (AIE). The underlying reactivity is enabled by alkynoyl intermediates, which are generated in a catalytic fashion and, thereby, open very mild entries to many consecutive one‐pot formations of luminophores. This account summarizes the multi‐component synthetic concept and presents very recent investigations on solid state and aggregation induced emissive systems.
2-Substituted 3-ethynylquinoxaline chromophores can be readily synthesized by a consecutive activation-alkynylation-cyclocondensation (AACC) one-pot sequence in a three-component manner. In comparison with the previously published four-component glyoxylation starting from electron-rich π-nucleophiles, the direct activation of (hetero)aryl glyoxylic acids allows the introduction of substituents that cannot be directly accessed by glyoxylation. By introducing N,N-dimethylaniline as a strong donor in the 2-position, the emission solvatochromicity of 3-ethynylquinoxalines can be considerably enhanced to cover the spectral range from blue-green to deep red-orange with a single chromophore in a relatively narrow polarity window. The diversity-oriented nature of the synthetic multicomponent reaction concept enables comprehensive investigations of structure-property relationships by Hammett correlations and Lippert-Mataga analysis, as well as the elucidation of the electronic structure of the emission solvatochromic π-conjugated donor-acceptor systems by DFT and time-dependent DFT calculations with the PBEh1PBE functional for a better reproduction of the dominant charge-transfer character of the longest wavelength absorption band.
3-Triazolylquinoxalines can be readily synthesized by applying two complementary synthetic protocols starting from heterocyclic p nucleophileso r( hetero)arylg lyoxylic acids in ac onsecutive four-or five-component reaction. Conceptually,t he sequential use of as ingle cuprous salt for alkynylation and Cu-catalyzed alkyne-azidec ycloaddition (CuAAC) in ao ne-pot fashion sets the stage for activation-alkynylation-cyclocondensation-CuAAC or glyoxylation-alkynyl-ation-cyclocondensation-CuAACs equences in good yields. The diversity-oriented generation of differently substituted 3-triazolylquinoxalines is an excellent entry to tunable emission solvatorchromic fluorophores with triazole ligation.T he electronic structure,c orroborated by DFT and TD-DFT calculations,r ationalizes the charge transfer character of relevant absorptions and large Stokes shifts as well as the electronic innocence of the triazole substituents.
The (3+ +3) anellation of alkynones and cyclic amidines is an ovel and unexpected approach to generate intensively blue luminescent tricyclic 2-aminopyridinium salts with quantum yields F f up to 63 %inwater.Byimplementation into ac onsecutive three-component reaction, these title compounds are obtained rapidly and efficiently in ad iversityoriented fashion. Most interestingly,t hese bi-and tricyclic 2aminopyridinium salts emit in dichloromethane and water solutions,t hus making them interesting novel luminophore probes for bioanalytics,aswell as in the solid state,thus making them blue emitters with tunable efficiency.Supportinginformation and the ORCID identification numbers for some of the authors of this article can be found under: https://doi.org/10.1002/anie.201808665.
Angewandte Chemie
Communications
Conflict of interestTheauthors declare no conflict of interest.
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