Synthesis and combined experimental and computational investigations on spectroscopic and photophysical properties of red emitting 3-styryl coumarins

• Synthesis of novel red emitting coumarins.
• DFT studies on the 4-cyano 3-styryl coumarins.
• Photophysical and spectroscopic studies of 4-cyano 3-styryl coumarins.

The coumarin derivatives are though highly fluorescent, lack in the absorption and emission in the red region. Modifying them to red emission included the strategy of formylation of 7-(N,N-diethyl amino) coumarin by Vilsmeier–Haak reaction followed by oxidative cyanation. The aldehyde synthesized was reacted with cyanomethyl benzoxazole/benzothiazole to give target compounds. All the compounds were characterised by spectral analysis. The cyanated molecules are found to be red shifted in absorption and emission by 90–100 nm. There was an increase in the quantum yield by about 10 times. The solvent polarity plots revealed the charge transfer process in the synthesized molecules and higher excited state to ground state dipole moment ratio. Density functional theory computations were performed to understand the nature of transitions involved in absorption and emission process.

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