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Materials 2017, 10(5), 512; doi:10.3390/ma10050512

Femtosecond Two-Photon Absorption Spectroscopy of Poly(fluorene) Derivatives Containing Benzoselenadiazole and Benzothiadiazole

1
Instituto de Ciência e Tecnologia, Universidade Federal de Alfenas, Poços de Caldas, MG 37715-400, Brazil
2
Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, SP 13566-590, Brazil
3
Departamento de Ciencias Naturales y Exactas, Universidad de la Costa, Barranquilla 080002, Colombia
4
Departamento Acadêmico de Química e Biologia, Universidade Tecnológica Federal do Paraná, Curitiba, PR 81280-340, Brazil
*
Author to whom correspondence should be addressed.
Academic Editor: Qing-Hua Xu
Received: 19 January 2017 / Revised: 19 April 2017 / Accepted: 28 April 2017 / Published: 7 May 2017
(This article belongs to the Special Issue Two-Photon Absorption Materials)
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Abstract

We have investigated the molecular structure and two-photon absorption (2PA) properties relationship of two push–pull poly(fluorene) derivatives containing benzoselenadiazole and benzothiadiazole units. For that, we have used the femtosecond wavelength-tunable Z-scan technique with a low repetition rate (1 kHz) and an energy per pulse on the order of nJ. Our results show that both 2PA spectra present a strong 2PA (around 600 GM (1 GM = 1 × 10−50 cm4·s·photon−1)) band at around 720 nm (transition energy 3.45 eV) ascribed to the strongly 2PA-allowed 1Ag-like → mAg-like transition, characteristic of poly(fluorene) derivatives. Another 2PA band related to the intramolecular charge transfer was also observed at around 900 nm (transition energy 2.75 eV). In both 2PA bands, we found higher 2PA cross-section values for the poly(fluorene) containing benzothiadiazole unit. This outcome was explained through the higher charge redistribution at the excited state caused by the benzothiadiazole group as compared to the benzoselenadiazole and confirmed by means of solvatochromic Stokes shift measurements. To shed more light on these results, we employed the sum-over-states approach within the two-energy level model to estimate the maximum permanent dipole moment change related to the intramolecular charge transfer transition. View Full-Text
Keywords: two-photon absorption; organic materials; polymers; tunable Z-Scan technique; nonlinear optics two-photon absorption; organic materials; polymers; tunable Z-Scan technique; nonlinear optics
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MDPI and ACS Style

Gonçalves Vivas, M.; Dario Fonseca, R.; de Paula Siqueira, J.; Renato Mendonça, C.; Rodrigues, P.C.; De Boni, L. Femtosecond Two-Photon Absorption Spectroscopy of Poly(fluorene) Derivatives Containing Benzoselenadiazole and Benzothiadiazole. Materials 2017, 10, 512.

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