DFT study of the infrared and Raman spectra of photochromic Fulgide; 3-Dicyclopropylmethylene-4-E-[1-(2,5-dimethyl-3-furyl)ethylidene]-5-(4-nitrophenylcyanomethylenetetrahydrofuran-2-one

The present work reports a theoretical study of vibrational signatures of the photochromic molecular transformation between two photochromic heterocyclic isomers. Raman and infrared (IR) spectra of the E (ring-opened form) and C (ring-closed form) photoisomers of 3-Dicyclopropylmethylene-4-E-[1-(2,5-dimethyl-3-furyl)ethylidene]-5-(4-nitrophenylcyanomethylenetetrahydrofuran-2-one have been calculated in gas phase in the region of 3500–500 cm −1 for both molecules in their ground state. Calculations of the structure parameters and frontier molecular orbitals were carried out using ab initio electronic structure theory at the Hartree-Fock, density functional theory, and Moller-Plesset perturbation theory levels, while calculations of the IR and Raman spectra were carried out using density functional theory with B3LYP functional and 6-31+g(d,p) basis set. After comparing the predicted spectra of both E-form and C-form, we were able to probe the changes that arise upon the ring-closure/ring-opening transformation. The computational results showed that the C-form is ≈ 10.7 kcal/mol lower in energy than the E-form. In addition, two different derivatives were adopted for both E-form and C-form to demonstrate the effect of substituents on the stability of the photoisomers. The theoretical predictions agree well with the reported experimental data, accounting for the molecular structure transformation of the photochromic isomers.