Synthesis and crystal structure of 3-(4′-nitrophenyl)iminocoumarin, and cyclization reaction mechanism based on DFT calculation

• A convenient and novel cyclization reaction for synthesizing 3-(4′-nitrophenyl)iminocoumarin is reported.
• Its crystal structure shows that title molecules aggregate to lamellar π–π stacked structural materials.
• The mechanisms of the cyclization reactions were postulated based on TD-DFT calculations.

A convenient method was reported to synthesize 3-(4′-nitrophenyl)iminocoumarin by a cyclization reaction following a Knoevenagel reaction of 2-hydroxybenzaldehyde with 4-nitrophenylacenitrile in an ethanol solution. Piperidine or piperazine was employed respectively as catalyst. Crystal structure of 3-(4′-nitrophenyl)iminocoumarin shows that the molecules are H-aggregation due to π–π stacking and hydrogen bonds between adjacent molecules, as a result, electrons would transfer easily from a molecule to an adjacent molecule. Based on theoretical calculations of the electronic structures and thermodynamic parameters of the reactive intermediates in these cyclization reactions, the reaction mechanisms were postulated. Data of single crystal and spectrum of UV–vis absorption show that 3-(4′-nitrophenyl)iminocoumarin is good π-conjugated compound and would be potentially employed as donor–acceptor polymer units for developing bulk heterojunction solar cell. This paper suggests a convenient and effective method for synthesizing ring-locked D–A copolymer units for developing solar cell materials.

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