Synthesis of 1,4-dihydropyridines under solvent free conditions and investigation of their photo physical properties

Synthesis of five 4-aryl substituted 1,4-dihydropyridines was developed following condensation of multi component reaction strategy using yttrium triflate as a catalyst. The absorption and fluorescence properties of structurally related 4-aryl 1,4-dihydropyridines in different solvents of varied polarities was investigated. The absorption maxima of these compounds follow no order of solvent polarity and nature of substitution. The spectral characteristics are solvent and compound specific. Fluorophores with electron withdrawing group have larger fluorescence quantum yields and greater solvatochromism than the compounds with electron donating groups. Protic solvents yielded higher fluorescence quantum efficiency. The chemical shift of the proton attached to C-4 and the carbonyl stretching frequency of bis acetyl groups at 3 and 5-positions exhibited a linear relationship with Hammett's para substituent constants while no such relationship exists between the latter and electronic absorption maxima, fluorescence emission maxima, fluorescence quantum efficiency and Stokes shift.

The chemical shift of the proton attached to C-4 in 1H NMR and the carbonyl stretching frequency of bis acetyl groups at 3 and 5-positions in 4-aryl-1,4-dihydropyridines exhibited a linear relationship with Hammet's substituent constants. However no such relationship exists between the Hammet's substituent constants and the electronic absorption maxima, fluorescence emission maxima, fluorescence quantum efficiency and Stokes shift.Figure optionsDownload as PowerPoint slideHighlights
► The paper deals with the synthesis of 1,4-dihydropyridines using Y(OTf)3 as catalyst.
► The 1,4-dihydropyridines are not bright fluorescent but are dim fluorescent.
► The photo physical properties of these molecules are solvent and substituent dependent.