چكيده لاتين
This work aims to investigate the ultrafast excited state deactivation of a Chalcone-based system, 2-hydroxychalcone, based on the ab initio quantum mechanical calculations. At the first step, ab initio methods have been employed to investigate the relaxation mechanisms in 2-hydroxychalcone system. In this regard, the potential energy curves related to the intramolecular hydrogen transfer process along the C7H13 bond length coordinate of this system have been investigated at the MP2/ADC(2) theoretical level. It has been predicted that structural rotation around the dihedral angle of C1C2C8O22 would cause the excited system to return to the electronic ground state via an ultrafast internal conversion. The results showed that non-radiative relaxation in this system from the first electronic 1ππ* state to the ground occurred by reaching the S1/S0 conical intersection in the potential energy curve of structural rotation without energy barrier. Also, the effect of changing the geometric structure on the photophysical behavior of the 2-hydroxychalcone system has been investigated using the 4, 2ʹ, 4ʹ-trihydroxychalcone system. Investigation of potential energy curves for the aforementioned system in line with the E-Z photo isomerization process led to a conical intersection between the electronic ground state and the first electronic excited state 1ππ*, and it was found that if the intramolecular hydrogen transfer process is not possible, the system undergoes the E-Z photo isomerization process.
Morover, quantum chemical computational methods have been used to investigate the non-radiative relaxation mechanism of the 2-hydroxychalcone system in the aqueous solvent environment with both implicit and explicit solvent models. In the calculations of the electronic transitions of the system in the presence of water solvent, the 1ππ* state has been significantly stabilized to be the first electronic transition of the system. Also, in the potential energy curves related to the intramolecular hydrogen transfer process in the presence of up to 3 water molecules, a conical intersection has been predicted at the MP2/ADC(2) theoretical level between the electronic ground state, S0 and the first electronic excited state, ππ*. Also it has been found that intramolecular hydrogen transfer process in the 2’-hydroxychalcone system in the presence of up to 3 water molecules, is accompanied by structural rotation.
