“Face-to-back” photo-cyclodimerization of the malonaldehyde enol form with the strong intramolecular H-bond: A TD DFT theoretical study

In this investigation we discussed one possible mechanism of the photoinduced cyclodimerization of two malonaldehyde molecules to form the “face-to-back” cyclodimer. Linear interpolation in internal coordinates approach was applied to study the excited-state relaxation mechanisms at the TD DFT level with aug-cc-pVDZ basis functions. It was found that the formation of the cyclodimer occurs through the first ¹ππ∗ excited state which has a charge transfer character. We also found a radiationless relaxation path of the ¹ππ∗ excited state mediated by a S_o–S₁ conical intersection.