# Halochromic Switch from the 1stto 2ndNear Infrared Window of Diazapentalene-Dithienosilole Copolymers

Christine Lartigau-Dagron, Wissem Khelifi, Hussein Awada, Katarzyna

Brymora, Sylvie Blanc, Lionel Hirsch, Frédéric Castet, Antoine Bousquet

► To cite this version:

Christine Lartigau-Dagron, Wissem Khelifi, Hussein Awada, Katarzyna Brymora, Sylvie Blanc, et al.. Halochromic Switch from the 1stto 2ndNear Infrared Window of Diazapentalene-Dithienosilole Copolymers. 2019 MRS Fall Meeting & Exhibit, Natalie Banerji, University of Fribourg R Demadrille, CEA Natalie Stingelin, Georgia Tech, Dec 2019, Boston, United States. hal-04185931

HAL Id: hal-04185931

https://univ-pau.hal.science/hal-04185931v1

Submitted on 23 Aug 2023

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Halochromic switch from the 1st to 2nd Near Infrared window of
Diazapentalene-Dithienosilole copolymers

Wissem Khelifi<sup>a</sup>, Hussein Awada<sup>a</sup>, Katarzyna Brymora<sup>b</sup>, Sylvie Blanc<sup>a</sup>, Lionel Hirsch<sup>c</sup>,
Frédéric Castet<sup>b</sup>, Antoine Bousquet<sup>a</sup>, <u>Christine Lartigau-Dagron</u><sup>a</sup>

Up to now, halochromism has mostly been demonstrated on chromophores absorbing in the UV-
visible range. However, research in the field of Infra-Red (IR) technologies is in strong development,
driven by technological needs in military and civilian applications, such as imaging, optical
communications, energy or sensing.[1] Also, since 50 % of the solar energy falls into the IR spectral
region, photovoltaic materials are under development to increase solar cells efficiency.[2] IR-materials
are also synthesized for biosensing and bioimaging because IR light penetrates into tissues, the so-
called “biological window”.[3] To design organic IR materials, the basic principle is to reduce the
bandgap. Specifically, synthesis of electron donor-acceptor (D-A) alternating conjugated copolymers
has demonstrated high potential to decrease the bandgap under 1.5 eV, leading to IR-absorbing or
emitting materials.[4] For the moment, most of these organic materials showed a maximum
absorption peaks falling in the first NIR optical window covering 750-1000 nm. Actually, the second
NIR optical window covering 1000-1350 nm is more promising for biological applications due to its
higher photothermal conversion and deeper tissue penetration.[5]

In this presentation, we will report the synthesis of a low bandgap copolymer based on the 2,5-diazapentalene (DAP) unit, derived from the diketopyrrolopyrrole (DPP) chromophore. We combine the strong acceptor DAP unit with the dithienosilole (DTS), a photostable electron donor [6] that allows the introduction of solubilizing alkyl chains onto the silicon atom. As the result of the polymerization, an IR-material was synthesized with a maximum absorption at 850 nm in chloroform solution. Upon protonation of the DAP unit with Brønsted acids or its complexation with Lewis acids, the maximum of absorption is further shifted up to 1100 nm (edge at 1500 nm) in the second NIR optical window. To the best of our knowledge, this halochromic behavior is the highest reported up to now. Using a combination of spectrometry, cyclic voltammetry and DFT calculations, we identified the Brønsted and Lewis adducts that are formed. We can demonstrate that this optical shift is correlated with a decrease of the copolymers bandgap associated to the decrease in the LUMO energy and enhancement of the pi-electron delocalization along the conjugated backbone, as revealed by the lowering of the bond length alternation.[7]

Acknowledgments: Agence Nationale de la Recherche (TAPIR project no. ANR-15-CE24-0024-02) and Région Nouvelle Aquitaine (TAMANOIR project no. 2016-1R10105-0007207) for their financial support. Pôle Modélisation HPC facilities of the Institut des Sciences Moléculaires, co-funded by the Nouvelle Aquitaine region, as well as by the MCIA (Mésocentre de Calcul Intensif Aquitain) resources of the Université de Bordeaux and of the Université de Pau et des Pays de l'Adour for computer times.

<footnote><sup>a</sup> CNRS/ Univ Pau & Pays Adour/ E2S UPPA, Institut des Sciences Analytiques et de Physicochimie pour l'Environnement et les Matériaux, UMR 5254, 64000, PAU, FRANCE</footnote>

<footnote><sup>b</sup> Institut des Sciences Moléculaires (ISM, UMR CNRS 5255), Université de Bordeaux, 351 cours de la Libération, 33405 Talence, France</footnote>

<footnote><sup>c</sup> Laboratoire de l'Intégration du Matériau au Système (IMS, UMR CNRS 5218), Université de Bordeaux, ENSCBP, 16 Avenue Pey-Berland, 33607 Pessac Cedex, France</footnote>
[1] Myochin, T.; Kiyose, K.; Hanaoka, K.; Kojima, H.; Terai, T.; Nagano, T. *JACS* **2011**, *133* (10), 3401

[2] a) Ameri, T.; Khoram, P.; Min, J.; Brabec, C. J., *Adv. Mater.* **2013**, *25* (31), 4245; b) Hendriks, K. H.; Li, W.; Wienk, M. M.; Janssen, R. A. J. *JACS* **2014**, *136* (34), 12130

[3] Croissant, J. G.; Zink, J. I.; Raehm, L.; Durand, J.-O., *Adv. Healthcare Mater.* 1701248-n/a.

[4] Liu, C.; Wang, K.; Gong, X.; Heeger, A. J., *Chem. Soc. Rev.* **2016**, *45* (17), 4825; b) Qi, J.; Qiao, W.; Wang, Z. Y., *Chemical Record* **2016**, 1531

[5] He, Y.; Cao, Y.; Wang, Y., *Asian J. Org. Chem.* **2018**, *7* (11), 2201

[6] Cheng, P.; Zhan, X., *Chem. Soc. Rev.* **2016**, *45* (9), 2544

[7] Khelifi, W.; Awada, H.; Brymora, K.; Blanc, S.; Hirsch, L.; Castet, F.; Bousquet, A.; Lartigau-Dagron C., *Macromolecules* **2019**, under revision