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Zucolotto Cocca LH, Pelosi AG, Abegão LMG, de Q Garcia R, Mulatier JC, Pitrat D, Barsu C, Andraud C, Mendonça CR, Vivas MG, De Boni L. Unveiling the molecular structure and two-photon absorption properties relationship of branched oligofluorenes. Phys Chem Chem Phys 2023; 25:5021-5028. [PMID: 36722878 DOI: 10.1039/d2cp05189c] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Organic molecules have been intensively studied during the last few decades because of their photonics and biological applications. In this material class, the fluorene molecules present outstanding optical features, for example, high values of two-photon absorption (2PA) cross-sections, visible transparency, and high fluorescence quantum yield. Also, it is possible to improve the nonlinear optical response by modifying the fluorene molecular structure. In this context, herein, we have synthesized V and Y-shaped branching oligofluorenes containing two and three fluorene moieties in each branch. Such a molecular strategy may exponentially enhance the nonlinear optical response due to the coherent coupling among the molecular arms. Thus, we combined the use of femtosecond Z-scan spectroscopy and white light transient absorption spectroscopy (TAS) to understand the molecular structure and 2PA property relationship of branching oligofluorenes. The results show that there is a universal relationship between the 2PA cross-section and the effective π-electron number (Neff) given by σ2PA(GM) = (079 ± 0.03)Neff2, which is independent of the molecular shape (linear, V or Y-shaped). Therefore, the intramolecular charge transfer responsible for the cooperative effect among the branches does not occur. This statement is corroborated by the results of the femtosecond TAS technique.
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Affiliation(s)
- Leandro H Zucolotto Cocca
- Photonics Group, Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil.
| | - André Gasparotto Pelosi
- Photonics Group, Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil.
| | - Luis M G Abegão
- Grupo de Fotônica, Instituto de Física, Universidade Federal de Goiás, Goiânia, 74690-900, GO, Brazil
| | - Rafael de Q Garcia
- Photonics Group, Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil.
| | | | - Delphine Pitrat
- ENSL, CNRS, Laboratoire de Chimie UMR 5182, 46 allée d'Italie, 69364 Lyon, France
| | - Cyrille Barsu
- ENSL, CNRS, Laboratoire de Chimie UMR 5182, 46 allée d'Italie, 69364 Lyon, France
| | - Chantal Andraud
- ENSL, CNRS, Laboratoire de Chimie UMR 5182, 46 allée d'Italie, 69364 Lyon, France
| | - Cleber R Mendonça
- Photonics Group, Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil.
| | - Marcelo G Vivas
- Laboratório de Espectroscopia Ótica e Fotônica, Universidade Federal de Alfenas, 37715-400 Pocos de Caldas, MG, Brazil
| | - Leonardo De Boni
- Photonics Group, Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970 São Carlos, SP, Brazil.
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Dos Santos CHD, Ferreira DL, Zucolotto Cocca LH, Mourão RS, Schiavon MA, Mendonça CR, De Boni L, Vivas MG. Size-dependent photoinduced transparency in colloidal CdTe quantum dots in the strong confinement regime: an inverse linear relationship. Phys Chem Chem Phys 2022; 25:359-365. [PMID: 36477139 DOI: 10.1039/d2cp05006d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Nanomaterials have been investigated as saturable absorbers for ultrafast lasers because of their large photoinduced transparency related to ground-state bleaching. However, the quantum dot size effect on the photoinduced transparency in the strong confinement regime has not been explored due to the challenge of accurately measuring the ground state and the excited-state absorption cross-sections. At the same time, these optical properties are essential to calculate several chemical and physical quantities at the nanoscale. In this context, we have employed the photoluminescence saturation method to determine the ground-state absorption cross-section and the femtosecond open-aperture Z-scan technique to investigate the size-dependent ground-state bleaching of glutathione-capped CdTe QDs synthesized in an aqueous medium. The results were modeled using rate equations within the three-energy levels approach. Our results pointed out that the photoinduced transparency rate at the 1S3/2(h) → 1S(e) transition peak presents an inverse linear relationship with the QD diameter (from 2.2 nm up to 3 nm). Otherwise, the larger QDs have a higher ground-state cross-section, which is directly proportional to the ground-state bleaching. To explain this apparent contradiction, we calculate the effective absorption coefficient αeff = σ/V (σ is the absorption cross section and V is the QD volume) for the QDs and observed that the smaller QDs have a higher absorption from the ground to the first excited state, corroborating our results. Finally, our results showed that the saturable absorption effect in CdTe-QDs is slightly higher than that obtained for graphene and other 2D materials and smaller than the black phosphorus in the visible region.
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Affiliation(s)
- Carlos H D Dos Santos
- Laboratório de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil. .,Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Diego L Ferreira
- Laboratório de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil.
| | - Leandro H Zucolotto Cocca
- Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Rafael S Mourão
- Grupo de Pesquisa em Química de Materiais, Universidade Federal de São João del-Rei, São João del-Rei, MG, Brazil
| | - Marco A Schiavon
- Grupo de Pesquisa em Química de Materiais, Universidade Federal de São João del-Rei, São João del-Rei, MG, Brazil
| | - Cleber R Mendonça
- Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Leonardo De Boni
- Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Marcelo G Vivas
- Laboratório de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil.
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