Evidence of acid mediated enhancement of photoinduced charge transfer reaction in 2-methoxy-4-(N,N-dimethylamino)benzaldehyde: Spectroscopic and quantum chemical study

The photophysical behavior of 2-methoxy-4-(N,N-dimethylamino)benzaldehyde (2-MDMABA) has been investigated by steady state absorption and emission spectroscopy, time resolved emission spectroscopy and quantum chemical calculations. The molecule 2-MDMABA having a weak acceptor aldehyde group shows strong local emission in all solvents and a weak solvent polarity dependent red shifted emission in polar aprotic solvents for the charge transfer (CT) state which follows well the Lippert–Mataga equation. Instead of usual protonation at the donor site with inhibition of CT process, protonation at the acceptor aldehyde site enhances acceptor properties and hence increases excited state charge transfer reaction. The ground state structural calculation at Density Functional Theory (DFT) level with B3LYP functional and 6-31++ G** basis set and potential energy surfaces (PESs) following twisted intramolecular charge transfer model by using DFT method in the gas phase and in acetonitrile solvent have been performed for the neutral and cation to correlate with experimental findings.