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Banca de QUALIFICAÇÃO: LEONARDO MARTINS CARNEIRO

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : LEONARDO MARTINS CARNEIRO
DATA : 03/05/2022
HORA: 14:00
LOCAL: https://conferenciaweb.rnp.br/webconf/fernando-28
TÍTULO:

Mechanisms for the deactivation of the electronic-excited states of α-(2-hydroxyphenyl)-N-phenylnitrone: from intramolecular proton and charge transfers to structure twisting and aggregation.


PÁGINAS: 29
RESUMO:

The search for new prominent chemosensors is significantly related to the rationalization of possible pathways involved in the deactivation of excited states. These include excited-state intramolecular proton transfer (ESIPT), twisted intramolecular charge transfer (TICT), and aggregation-induced emission (AIE) as alternative pathways for the commonly observed fluorescence decay and non-radiative deactivation. We have studied the compound α-(2-hydroxyphenyl)-N-phenylnitrone (Nit-OH), particularly aiming at the observation of multi-pathways of excited-state deactivation. We experimentally observed that Nit-OH is stable in acetonitrile solution under UV-Vis light, an uncommon feature among nitrone derivatives. Using the nudged elastic band method, we obtained a 40 kcal mol–1 barrier for the conversion of Nit-OH to its corresponding oxaziridine at the S0, whilst the energy minimum at the S1 is close to the nitrone geometry, preventing decay to the transition state of the oxaziridine path, thus, explaining the Nit-OH stability. The experimentally observed 540 nm fluorescence for Nit-OH was shown to be related to excitation at 360 nm (HOMO-LUMO transition, at the TD-PBE0/6-31+G(d,p)/SMD(ACN) theoretical level). Potential energy curves (PEC) for the S1 state of Nit-OH did show that there are structures associated with ESIPT, involving an intramolecular hydrogen interaction between the nitrone-O and phenolic groups; the existence of this H-bonding was also confirmed using X-ray powder diffraction. TICT takes place following the proton transfer within ESIPT and a non-radiative deactivation at the S1/S0 conical intersection occurs. Fluorescence is only possible if TICT is prevented and, since the 540 nm emission increases with the Nit-OH concentration, we assumed that AIE is taking place here. Moreover, the possibility of an anti-Kasha emission from the S2 was proposed based on the dependence of the fluorescence excitation wavelength on Nit-OH concentration. From the calculation of the PEC for the S2 state, we obtained radiative transitions at 379 and 432 nm, similar to the obtained experimental values of 383 and 453 nm. ESIPT seems to occur at the S2 state, although TICT is not possible, as indicated by the PEC and further confirmed by the corresponding calculated molecular electrostatic potential surfaces. Finally, we proposed a Jablonski-like diagram that depicts all experimental and theoretical electronic transitions for Nit-OH, summarizing the unique complex photophysical behavior of this nitrone derivative.


MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1939561 - FERNANDO HEERING BARTOLONI
Membro Titular - Examinador(a) Interno ao Programa - 1544379 - ANDERSON ORZARI RIBEIRO
Membro Titular - Examinador(a) Interno ao Programa - 312.257.708-90 - YURI ALEXANDRE AOTO - NENHUMA
Membro Suplente - Examinador(a) Interno ao Programa - 1864481 - HUEDER PAULO MOISES DE OLIVEIRA
Notícia cadastrada em: 14/04/2022 11:51
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