Name of the laboratory:  IM2NP UMR CNRS 7334 (www.im2np.fr)

(Institut Matériaux Microélectronique Nanosciences de Provence), ISEN-Toulon

Thesis advisor:  Lionel Patrone (researcher at CNRS – HDR)

Email and address: lionel.patrone@im2np.fr, phone: +33 (0) 483 361 984

IM2NP - CNRS UMR 7334, ISEN-Toulon, Maison du Numérique et de l’Innovation, Place G. Pompidou, 83000 Toulon, France

Co-advisor: Virginie Gadenne, virginie.gadenne@im2np.fr

Subject’s title: Surface functionalization by self-assembled monolayers of novel push-pull chromophores: photoelectric properties and application to bio-sensors  

Subject description:

Push-pull chromophores provide an intramolecular charge separation between a Donor and an Acceptor groups via a spacer (Fig. 1a). Such an effect can be exploited in various fields such as nonlinear optics, solar cells [1], in the modification of the workfunction and the interface with electrodes, or the formation of a high dielectric permittivity layer [2] beneficial in micro-nanoelectronics, or in photovoltaics to hinder the recombination of photogenerated excitons. For this purpose, it is essential to orient all the dipoles in the same direction and to avoid head to tail arrangement. Self-assembled monolayers [3] of chromophores grafted on the surface is a very promising strategy making it possible for the chromophore to organize in the same orientation which is necessary to obtain controlled collective phenomena (Fig. 1b). Previous works on push-pull dealt with charged molecules which can hinder the organization by the effect of repulsion between charges. In this work, we propose to focus on the formation of ordered SAMs of original non-charged push-pull chromophores based on the expertise developed in the laboratory [4, 5]. We will work in close collaboration with the chemists of CINaM in Marseille about the development of non-charged push-pull chromophores which could ensure a good organization of the SAMs and an effective charge separation. For that, the use of DFT calculations to assess the electronic properties and the charge separation in the molecule will be very useful. In order to broaden the light absorption spectrum of the layer – which is important for photovoltaics for example - and/or the electrical properties of the push-pull SAM, two approaches could be explored: the elaboration of mixed layers of self-assembled chromophores and the innovative use of original structures including at least two (or even three) different chromophores with complementary absorption and electrical properties that will be designed and synthesized (Fig. 1c). These bi(tri)-chromophoric structures [6] will be supported by the same anchoring group. Such an original approach, that has not been yet studied in the literature, will locally expand the absorption and electronic properties and generate uniform and well-defined SAMS. Various combinations of Donor, Acceptor, and spacer groups will be tested (Fig. 1d). The quality of the layers produced will be evaluated by various surface analysis techniques available in the laboratory (ellipsometry, contact angles, UV-visible spectroscopies, infrared, XPS, UPS, IPES ...), and in particular at the local level by atomic force and electric force microscopy (AFM, EFM) and scanning tunneling microscopy (STM). Then, the electric properties will be studied via capacitance-voltage (C-V) and current-voltage (I-V) analyzes locally by STM/EFM microscopy, and more generally by means of metallic electrical contacts obtained by vacuum evaporation through a mask, or via an InGa droplet at the eutectic.

Figure 1 (a): Structure of the "push pull" planned; (b): scheme of push-pull SAMs; (c): bi-chromophore structure with complementary absorption on the same grafting head; (d): Acceptor (top) and donor (bottom) examples. The spacer could be bi (or ter) thiophene.

Once the organization of the SAMs has been controlled, efforts will be made to create complementary chromophore binary layers diluted in a matrix of alkyl chains for application to biosensors with selective detection, in collaboration with biologists (e.g. PBS lab in Rouen). For this we will work on gold and silicon substrates with various chromophores each one owning a different polarization response for the same voltage. This polarization will be used to activate the deployment of an antigen allowing the detection of the complementary antibody (Fig. 2). Based on a preliminary work carried out in the lab, we will study on silicon the assembly of a matrix of alkyl chains with holes enabling to host and isolate the various chromophores bearing the antigens. In particular, the use of Raman spectroscopy exalted by a nanostructured gold surface (SERS mode) will make it possible to detect the selective adsorption of the antibodies [7].

Figure 2: principle of detection of antibodies by the voltage applied to the surface.

Bibliography:

1. V. Malytskyi, J.-J. Simon, L. Patrone, J.-M. Raimundo, RSC Adv. 5, 354-397 (2015); J. Roncali, P. Leriche, P. Blanchard Adv. Mater. 26, 3821 (2014)

2. Y.G. Ha, A. Facchetti, T.J. Marks, Chem. Mater. 21 1173 (2009); Y. Zhu et al., Polym. Chem. 10, 2447 (2019)

3. A. Ulman, An Introduction to Ultrathin Organic Films, Academic Press (Ed.), Boston (1991)

4. V. Malytskyi, J.−J. Simon, L. Patrone, J.−M. Raimundo, RSC Adv. 5, 26308-26315 (2015)

5. V. Malytskyi, V. Gadenne, Y. Ksari, L. Patrone, J.−M. Raimundo, Tetrahedron 73, 5738–5744 (2017)

6. A. Aster et al., Chem. Sci. 10, 10629 (2019)

7. B. Santos Gomes, E. Cantini, S.Tommasone et al., ACS Appl.Bio.Mater. 1, 738-747 (2018)

Funding: Doctoral contract from the ministry (MESRI)

Keywords: Self-assembled molecular monolayers, push-pull chromophores, photovoltaics, biosensors