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Benzothioxanthene and derivatives: promising building blocks for organic electronics – BTXI-APOGEE

Benzothioxanthene and derivatives: promising building blocks for organic electronics

Mainly used for its emissive properties (in only a few studies), BTXI has gone completely unnoticed within the community working in the field of organic electronics. Based on preliminary work by the group, the BTXI-APOGEE project aims at exploring different synthetic methodologies, thus leading to the characterization of new derivatives that will be subsequently embedded into various devices such as OLEDs and organic solar cells.

Make the BTXI a building block of choice

BTXI-APOGEE is a highly innovative and therefore challenging project since almost everything remains to be discovered. Great forgotten of the organic electronic success story, the benzothioxanthene turns out to be a promising and high potential block in terms of synthetic versatility and properties. As a result, in less than two years, and without man power truly dedicated to this topic, about ten articles were already published. Hence, considering the variety of chemical modifications and design principles targeted herein, it is undoubtable that scientific breakthroughs will be achieved along the project. As an exemple, new structures were already used in a large area, flexible and printed OLED. Moreover, scope of investigation of our structure was even and recently opened to another hot topic which is the photodynamic therapy.

The project is built around by three interconnected work packages (WPs).

- WP1. This WP is dedicated to the functionalization of the BTXI core (synthetic methodology) and the synthesis of new derivatives.
- WP2. The second WP will be a support of choice to 1) understand and simulate the reactivity of newly functionalized BTXI cores and 2) predict and then characterize the properties of target structures at the molecular level.
- WP3. The third WP will be devoted to the synthesis of new pi-conjugated materials (molecular and macromolecular) and their embedment in specific devices namely organic solar cells and OLEDs. The aim is to provide a fundamental understanding of the structure-properties relationships of the newly synthesized molecules.

Functionalization of the core:
Synthetic methodology was carried out to keep demonstrating the potential reactivity of the core since its early reported simple bromination, cornerstone of the grant application. As a starting point, the synthesis of BTXI was initially fully optimized in order to prepare large quantities (several hundred grams), in just two steps and without any columns. In parallel, work aimed at extending the p-conjugated system was also initiated and successfully acheived, leading to the preparation of new and original derivatives (manuscript in preparation).

Rationalization of structure/properties relationships (and thematic opening):
Owing to the active and complementary collaborators involved in this project, properties (optical and electrochemical) of new derivatives are systematically studied and rationalized (from an experimental and computational point of view). This in depth understanding between structures and properties revealed for some structures i) amazing electrochemical features with dual redox properties ( towards electrochromic and energy storage devices) and 2) the sensitization of singlet oxygen under illumination. The latter property opened doors to several new collaborations allowing «in vitro« (uterus, breast and pancreatic cancer) and «in vivo« (embryo of zebrafish) evaluation of few derivatives as potential new photosensitizers.

Integration of BTXI derivatives into devices:
In addition to an immersion in the world of living organisms and photodynamic therapy, several functionalized intermediates were used to prepared p-conjugated active material that were, in turn, embedded in demonstrators. As an example title, a dimer of BTXI was subsequently “N-annulated” and sent to our Canadian collaborator, Professor Gregory Welch. Perfectly soluble in xylene, thanks to the extra side chain brought by the N-annulation reaction, this new dimer was used as emissive material and printed on a plastic sheet to prepare large and flexible low cost OLED.

The functionalization of the core will obviously continue and depending on the properties highlighted by the different characterizations carried out within the frame of the project, different devices/applications will be targeted.
For instance, and in addition to the anticancer and vectorization aspect, water-soluble derivatives are currently in the pipeline to be used as interfacial layers in organic solar cells.

Papers :
1. Andrés Castan, J.M. ; Amruth, C. ; Josse, P. ; Abad Galan, L.; Simón Marqués, P.; Allain, M.; Maury, O.; Le Bahers, T.; Blanchard, P.; Monnereau, C.; Cabanetos, C. “ Thiochromenocarbazole Imide: A new organic dye with first utility in large area flexible electroluminescent devices” Materials Chemistry Frontiers, 2022, DOI: 10.1039/d2qm00299j

2. Deiana, M. ; Josse, P. ; Dalinot, C. ; Osmolovskyi, A. ;, Simón Marqués, P. ; Andrés Castán, J.M. ; Abad Galán, L. ; Allain,M. ; Khrouz, L. ; Maury, O. ; Le Bahers, T. ; Blanchard, P. ; Dabos-Seignon, S. ; Monnereau, C. ; Sabouri, N. ; Cabanetos, C. « Site-Selected Thionated Benzothioxanthene as Heavy-Atom-Free Small-Molecule Photosensitizers for Photodynamic Therapy » Nature Comm Chem, 2022, just accepted

3. Josse, P. ; Morice, K. ; Puchan, D.; Ghanem, T.; Blanchard, P.; Cabanetos, C. “Revisiting the synthesis of the benzothioxanthene imide five decades later “ New Journal of Chemistry, 2022, 2022, 46, 8393 + Cover picture

Patent : “Novel compounds and their use as photodynamic agents” inventeurs: Nasim Sabouri, Marco Deiana, Cyrille Monnereau et Clément Cabanetos: 2021006022VFT-Fotody, Application number:2230258-2

Organic electronics, pipe-dream few decades ago, is now a reality with commercially available Organic light emitting diode based displays (TVs, smartphones), sensors, batteries or photovoltaics (OPVs). Hence, the advent of such research field has generated a craze in the scientific community leading to the synthesis and characterization of various classes of pi-conjugated molecular and macromolecular semiconductors. Among them, imide-containing rylenes have attracted considerable research attention due to their redox, electron-withdrawing and charge-carrier transport properties, as well as their excellent chemical, thermal, and photochemical stabilities.
Naphthalene diimide (NDI) and perylene diimide (PDI) can be unequivocally recognized as the most studied imide based building blocks for the preparation of high-performance electron transporting optoelectronic materials. Within these wide-ranging studies, considerable effort has been undertaken to functionalize both the bay positions and the nitrogen atom constituting the imide group (N-positions) to bring solubility, tune the molecular (opto)electronic characteristics, and build extended ?-conjugated architectures.
A contrario, the N-(alkyl)benzothioxanthene-3,4-dicarboximide (BTXI), a sulfur containing rylene-imide dye, has not triggered such research interest. Among the very scarce publications, the later was exclusively dedicated to its remarkable fluorescent properties in biological and polymer staining applications. Moreover, from a chemical point of view, the BTXI was solely functionalized on the N-position for post-grafting purpose and/or to increase solubility resulting, once again due to a lack of interest, in limited range of characterizations and applications. In this context, and base on self-initiated fundamental work on the selective mono-bromination of the BTXI core, the aim of the BTXI-APOGEE project is to explore different synthetic methodologies to further functionalize the BTXI core, thus leading to the characterization of new and original molecular and macromolecular derivatives which will be finally embedded in specific devices namely OLEDs and organic solar cells.

Project coordination


The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.



Help of the ANR 180,407 euros
Beginning and duration of the scientific project: March 2021 - 42 Months

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