Synthesis, electronic, and spectral properties of novel geranylated chalcone derivatives: a theoretical and experimental study

Novel chalcone derivatives with different substituents attached to A and B-rings: hydroxyl, methoxyl, geranyl, and prenyl groups were synthesized. The obtained compounds were characterized by NMR, HRMS, UV-Vis, IR, and MS. The theoretical analysis was carried out in all the compounds using density functional theory (DFT) with the B3LYP, PBE0, and M06-2X functionals in combination with the 6-311G(d,p) Pople-type basis set. The excited state properties were calculated by time dependent density functional theory (TD-DFT) using the same methodology applied for the ground state properties. The calculated vertical absorption wavelengths (lambda(max)) in gas phase and in ethanol as a solvent are consistent with the experimental ones, being the TD-DFT: B3LYP/6-311G(d,p) and PCM-TD-DFT: PBE0/6-311G(d, p) the best methodologies for these calculations with good approximation to the experimental values. The calculated reorganization energies indicated that, the four chalcone derivatives present an electron transfer character due to the smaller registered values. From these parameters it is proposed that these show an n-type semiconductor character. The localization of the frontier orbitals (HOMO and LUMO) shows that only the compound containing a hydroxyl group on the A-ring displays a marked delocalization favoring the charge-transfer process in this system. The HOMO-LUMO gap energies indicate that the inclusion of different donor groups in the rings does not improve the obtained values for this property.