Anais do Workshop INEO 2023

UNRAVELING THE ICT CHARACTER IN D-A COPOLYMERS: AN EXPERIMENTAL AND THEORETICAL APPROACH

Published in 12/12/2023 - ISBN: 978-65-272-0088-8

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Paper Title
UNRAVELING THE ICT CHARACTER IN D-A COPOLYMERS: AN EXPERIMENTAL AND THEORETICAL APPROACH
Authors
  • Harison Jean de Toledo
  • Harison Jean de Toledo
  • Leonardo Tarczewski
  • Luis Octavio de Araujo
  • ANDREIA GERNISKI MACEDO
  • P. C. Rodrigues (Pq); UTFPR
Modality
Pôster
Subject area
Síntese e caracterização de materiais
Publishing Date
12/12/2023
Country of Publishing
Brasil
Language of Publishing
Inglês
Paper Page
https://www.even3.com.br/anais/workshop-do-ineo-2023/613241-unraveling-the-ict-character-in-d-a-copolymers---an-experimental-and-theoretical-approach
ISBN
978-65-272-0088-8
Keywords
diketopyrrolopyrrole, D-A copolymer, ICT
Summary
The donor-acceptor (D-A) approach, with alternating electron-rich (donor) and electron-deficient (acceptor) units along the conjugated polymer backbone, is an effective method to control the optical and redox properties of the conjugated copolymers. For D-A copolymers, the first photoexcitation is expected to correspond to a state where the excited electron is promoted to the first unoccupied orbital (LUMO), which is mainly localized at the acceptor moiety, while the hole is localized at the donor unit. This characteristic is usually named as internal charge transfer (ICT), a intrachain electron transfer from the electron-rich to the electron-deficient unit. Most of the works focused in D-A copolymers attributed the ICT transition based only on the dual-band absorption profile (“camel-back” profile) and are focused on its application in optoelectronic devices, presenting brief discussions about the material’s photophysics and redox properties. In this work, D-A copolymers composed of diketopyrrolopyrrole (DPP), thiophene (Th), benzothiadiazole (BT), and fluorene (F) as a building block have been designed, synthesized, and analyzed in terms of optical properties and theoretical studies. Two perfect alternated copolymers, PFBT and PFThDPPTh, containing F as electron donor moiety, and BT or Th-DPP-Th as electrons acceptors were synthesized using Suzuki cross-coupling reaction. The initial results presented that the perfect alternated copolymers exhibited the dual-band absorption profile, suggesting that both materials are D-A copolymers with ICT, as frequently related in the literature. However, our results using density functional theory (DFT) and time-dependent DFT (TD-DFT) frameworks contrasts with what is often observed and reported for other D-A copolymers for which charge transfer from a delocalized state to a state localized at the acceptor units is expected, indicating that although moieties with different electron-donating/withdrawing strengths were used, the final materials do not display the D-A character. The electronic spectra in solution and in film of the two materials showed the characteristic profile of D-A copolymers (bands with ?max in 317 and 445 nm for the PFBT and, 370 and 650 nm for PFThDPPTh), suggesting that the ICT process occurs in both structures. Although, analyzing partial and total densities of states (DOS) and the HOMO and LUMO spatial distributions for PFBT and PFThDPPTh oligomers, in the PFBT it is possible to see that the HOMO is mainly composed of the fluorene orbitals, while the LUMO is dominated by benzothiadiazole states. The same feature cannot be seen in the spatial distribution of HOMO and LUMO orbitals for the DPP derivative. The PFThDPPTh does not display D-A characteristics, although it is composed of an electron-withdrawing moiety (DPP) copolymerized with two electron-rich units (F and Th) and presents the “camel-back” signature in the electronic absorption spectra. Our results pointed out that the HOMO orbital has a major contribution from DDP, while in the LUMO, DPP and Th have similar contributions but are still being dominated by DPP. This is in stark contrast with what has been reported regarding D-A copolymers, showing that for these compounds, it is expected that the HOMO is formed mainly by the donor moieties and the LUMO by the acceptor units. We note that, until now, the designation of a given copolymer as D-A is quite cloudy, based primarily on the visualization of electronic absorption spectra: if a “camel-back” profile is observed, the material is potentially assigned as D-A. In this concern, our results demonstrate that the analysis of the composition of the near gap states is crucial to attribute the character of a given copolymer, avoiding misinterpretation of the results as such an assessment of the electronic structure reveals that, indeed the material reported here does not belong to the D-A class of copolymers.
Title of the Event
Workshop do INEO 2023
City of the Event
Nazaré Paulista
Title of the Proceedings of the event
Anais do Workshop INEO 2023
Name of the Publisher
Even3
Means of Dissemination
Meio Digital

How to cite

TOLEDO, Harison Jean de et al.. UNRAVELING THE ICT CHARACTER IN D-A COPOLYMERS: AN EXPERIMENTAL AND THEORETICAL APPROACH.. In: Anais do workshop INEO 2023. Anais...Nazaré Paulista(SP) Hotel Estância Atibainha, 2023. Available in: https//www.even3.com.br/anais/workshop-do-ineo-2023/613241-UNRAVELING-THE-ICT-CHARACTER-IN-D-A-COPOLYMERS---AN-EXPERIMENTAL-AND-THEORETICAL-APPROACH. Access in: 18/07/2025

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