Consecutive multicomponent syntheses of N-substituted 3-arylallylidene indolones - Solid-state emitters and photoisomerization

A series of variably substituted 3-arylallylidene indolones were synthesized as diastereomeric mixtures applying a novel consecutive three-component Heck-condensation sequence in the sense of a one-pot synthesis. The N-substitution pattern was found to be crucial for the fluorescence in the solid state. Accordingly, the synthetic route was extended to a consecutive four-component reaction to generate a diverse compound library of Boc-substituted 3-arylallylidene indolones. Studying the structure-property relationship by Hammett correlation revealed a discontinuous behavior of the longest wavelength absorption bands of these compounds. 3-Arylallylidene indolones exclusively fluoresce in the solid state. Exceptions are strongly donor-substituted derivatives, which also luminesce in solution and reveal positive emission solvatochromism. With the N-tosyl derivative, an AIE (aggregation induced emission) chromophore was discovered and for the (p-anisyl)2N-substituted derivative aggregation induced emission enhancement (AIEE) was found. The absorption spectra of the 3-arylallylidene indolones can be plausibly rationalized by TD(DFT) calculations. Interestingly, the diastereomers, which can be photoisomerized, are very similar in their photophysical properties.

Automated summary

A novel consecutive three-component Heck-condensation sequence was applied to synthesize a series of 3-arylallylidene indolones with variable substitutions as diastereomeric mixtures in a one-pot synthesis approach. The N-substitution pattern was found to be crucial for the fluorescence behavior in the solid state. The structure-property relationship was studied by extending the synthetic route to generate a diverse compound library of Boc-substituted 3-arylallylidene indolones, revealing discontinuous behavior of the longest wavelength absorption bands of these compounds.