Banca de DEFESA: ALEXANDER GARRETA GONCALVES COSTA PINTO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : ALEXANDER GARRETA GONCALVES COSTA PINTO
DATA : 02/08/2021
HORA: 09:30
LOCAL: meet.google.com/hfe-mjas-ypr
TÍTULO:

1,2,4,5-Tetraphenylimidazole derivatives applied in organic light emitting systems

PÁGINAS: 131
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Química Orgânica
ESPECIALIDADE: Físico-Química Orgânica
RESUMO:

Two series of 1,2,4,5-tetraphenylimidazole (TEPI) compounds were synthesized with different substituents on the 1-phenyl ring, which differed only by the absence (series a) or presence (series b) of an o-OH on the 2-phenyl ring. It was observed that the Excited State Intramolecular Proton Transfer (ESIPT) assigns significant differences in the photophysical characteristics of series b when compared to series a. After photoexcitation, there is a possible increase in the antiaromaticity of the system, due to the formation of a nodal plane that crosses from the 2-phenyl ring to the intramolecular hydrogen bond, favoring the occurrence of ESIPT. As consequence, longer emission wavelengths, higher Stokes Shift, and lower fluorescence quantum yields (Φ_FL) were reported. Electron-donor substituents, in general, had higher Φ_FL values. For series b, from a linear free-energy Hammett correlation, it was possible to prove the formation of a positive partial charge (ρ < 0) on processes linked to fluorescence decay. Bond lengths and dihedral angle values related to ESIPT were evaluated for series b; from a computational study based on the Atom in the Molecule Theory (AIM), it was possible to determine the critical boundary points (PC_r and PC_s) associated with the tautomeric process. Thus, with the insertion of a geometric factor, the appearance of a negative charge (ρ > 0) during the photoexcitation process was shown. The chemiluminescent assays showed that TEPI derivatives can be used as activators in the peroxyoxalate reaction, probably through the mechanism known as Chemically Initiated Electron Exchange Luminescence (CIEEL). Derivatives from series a exhibited lower values of Φ_S^∞and Φ_CL^∞, and higher k_CAT/k_D when compared to series b. Compared to other systems, series a derivatives had their chemiluminescent parameters analogous to inefficient activators. For series b, these values were equivalent to lophines and classical activators such as anthracene and 2,5-diphenyloxazole. Linear Hammett correlations using the parameters Φ_S^∞andk_CAT/k_D revealed that there is a possibility of an inverted CIEEL mechanism occurring during chemiexcitation, however, the determination of the electrochemical properties of these compounds is necessary to sustain this hypothesis.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1939561 - FERNANDO HEERING BARTOLONI
Membro Titular - Examinador(a) Interno ao Programa - 1544394 - PAULA HOMEM DE MELLO
Membro Titular - Examinador(a) Externo ao Programa - 1734908 - FABIO FURLAN FERREIRA
Membro Suplente - Examinador(a) Interno ao Programa - 1623774 - KARINA PASSALACQUA MORELLI FRIN
Membro Suplente - Examinador(a) Externo à Instituição - FABIANO SEVERO RODEMBUSCH - UFRGS