Banca de DEFESA: WENDEL MAGALHÃES WIERZBA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : WENDEL MAGALHÃES WIERZBA
DATE: 22/11/2023
TIME: 14:00
LOCAL: Virtual
TITLE:

Effects of 2,2'-bipyridine substituent coordinated to Re(I) for potential application of
CO₂ photoreduction

PAGES: 67
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Inorgânica
SPECIALTY: Foto-Química Inorgânica
SUMMARY:

The utilization of suitable forms to convert solar energy is one of the many ways to suply the world's energy demand. Transition metals and integrated photocatalysts can be used as photocatalysts, such as Re(I) coordination complexes that can be used to storage energy in chemical bonds  through CO₂ reduction, and modifications in their structure allow to change selectivity and efficiency. The presente work is part of this context and will investigate Re(I) complexes that follows fac-[Re(NN)(CO)₃Cl] type, in the conversion solar energy into chemical energy through CO₂ photoreduction, varying the substituints of 2,2’-bipyridine,  and investigate the correlation between the donor/aceptor capacity and  photochemical and photophysical properties and in photocatalytic CO2 reduction reactions. These processes and relationships are not yet fully understood, and these new study will be a significant contribution to this field of research, as they will help in the development of more efficient systems for converting solar energy into chemistry through CO₂ photoreduction.

Compounds of fac-[Re(NN)(CO)₃Cl] type, where NN = bpy, Mebpy, (CH₃O)bpy, Brbpy, (HO₂C)bpy and (H₃CO₂C)bpy, were prepared aiming to modulate the spectroscopic, electrochemical, photochemical and photophysical properties of the compounds as a function of the donor or acceptor character of the substituents. The presence of electron-withdrawing substituents resulted in a bathochromic shift of the absorption bands comparing to the complex without substituents (Rebpy), while the electron-donating substituents resulted in a hypsochromic shift of the absorption bands. Cyclic and differential pulse voltammetry showed that this trend regarding the charge acceptor/donor capacity of the substituents is maintained with the redox potentials of the compounds, so that the electron acceptor character of the substituents decreases the electron density in the metal center, causing its oxidation potentials more positive and its reduction potentials less negative, comparing to the complex without substituent. On the other hand, substituents with electron-donor character caused the opposite effect, in which their oxidation potentials decreased and their reduction potentials became more negative. Their emission spectra present broad and unstructured bands, with very similar profiles, differing by the maximum emission wavelengths and emission intensities, typically observed in the ³MLCT excited state photoluminescence of Re(I) carbonyl polypyridine compounds, with similar trend observed in the absorption spectra.

Photochemistry and photophysics experiments, using a sacrificial donor (TEOA) showed that the complexes have fast reductive suppression of ³MLCT states by TEOA, which reveals important information about the intermediate stability of the photocatalytic cycle of CO₂ reduction. The photophysical results showed a tendency in which complexes with electron-withdrawing substituents, Br, (HO₂C) and (H₃CO₂C), accommodate the negative charge on the one electron reduced specie formed after reductive suppression, while the eléctron-donor substituents have a negative effect, comparing to Rebpy. The formation and stability of the one-electron-reduced species (OERS) present in the photocatalytic cycle of CO₂ reduction was also investigated. The results showed dark decay lifetimes with the sequence Re-CH₃Obpy-Cl < Re-Mebpy-Cl < Re-bpy-Cl < Re-(HO₂C)bpy-Cl < Re-Brbpy-Cl, showing a possible dependence to the bipyridine ligand substituent. In the presence of CO₂, the decay of the OERS was shown to be faster in relation to the values measured under an argon atmosphere. This demonstrates that the one-electron reduced species of the complexes react with CO₂. The values of t_1/2 follow practically the same trend observed in the presence of argon, so that compounds with electron-withdrawing substituents have a longer lifetime in comparing to other substituents.

COMMITTEE MEMBERS:
Presidente - Interno ao Programa - 1671688 - ANDRE SARTO POLO
Membro Titular - Examinador(a) Interno ao Programa - 1544341 - WENDEL ANDRADE ALVES
Membro Titular - Examinador(a) Externo ao Programa - 1623774 - KARINA PASSALACQUA MORELLI FRIN
Membro Titular - Examinador(a) Externo ao Programa - 1544379 - ANDERSON ORZARI RIBEIRO
Membro Suplente - Examinador(a) Interno ao Programa - 1760527 - FLAVIO LEANDRO DE SOUZA
Membro Suplente - Examinador(a) Externo ao Programa - 2351974 - JULIANA DOS SANTOS DE SOUZA