Periodic Reporting for period 1 - TODAM (Transformation of Organic Dyes into Advanced Materials by Chemical Vapour Deposition)
Période du rapport: 2021-04-15 au 2023-04-14
Conjugated polymers are drawing a constantly growing interest for modern energy technologies, particularly for the clean production of hydrogen fuel by visible-light photo-electrocatalytic water splitting. Although conjugated polymer catalysts are reported as stable, low cost and versatile materials, current synthetic approaches (solution-based) have prevented the study of the most interesting motifs and hindered the integration and up-scaling of most conjugated polymers for practical applications. The central idea of the TODAM project built on the recent achievements of the host group in the chemical vapour deposition (CVD) reaction of chromophore-based conjugated polymers.
The main scientific objectives of the TODAM project were:
i) Establish oCVD conditions for the polymerisation DPP-derivatives into DPP-based conductive polymer thin films directly from the gas phase.
ii) Disclose new families of conjugated polymers and copolymers based on N-unsubstituted DPPs.
iii) Provide insights into the properties and potential of the formed DPP-based CPs toward solar-assisted fuel production, creating polymers with donor-acceptor structure and tuneable electronic structure.
iv) Study the generation, separation and transfer of charge processes in the DPP-based CP thin films and evaluate their potential for the efficient photo-electrocatalytic production of hydrogen.
The TODAM project effectively combined the expertise of the applicant and the supervisor to expand far beyond the state-of-the-art of conjugated polymers while investigating the gas phase polymerisation of industrial dyes, i.e. DiketoPyrroloPyrrole (DPP) derivatives. In spite of their remarkable properties, including an exceptional light resistance and unique physicochemical properties, conjugated DPP assemblies remain a largely unexplored topic due to the lack of synthetic approaches. The outcomes of the TODAM project are two-fold with i) the development of a oCVD route towards the synthesis, engineering and deposition of unreported non-N-alkylated DPP-based conjugated polymer thin films, and ii) the in-depth study of the photo-electronic and photo-electro-catalytic properties of the new conjugated polymers and the identification of promising building blocks for the preparation of photoanodes and photocathodes for the production of hydrogen from solar-assisted water splitting.
The main scientific objectives of the TODAM project were:
i) Establish oCVD conditions for the polymerisation DPP-derivatives into DPP-based conductive polymer thin films directly from the gas phase.
ii) Disclose new families of conjugated polymers and copolymers based on N-unsubstituted DPPs.
iii) Provide insights into the properties and potential of the formed DPP-based CPs toward solar-assisted fuel production, creating polymers with donor-acceptor structure and tuneable electronic structure.
iv) Study the generation, separation and transfer of charge processes in the DPP-based CP thin films and evaluate their potential for the efficient photo-electrocatalytic production of hydrogen.
The TODAM project effectively combined the expertise of the applicant and the supervisor to expand far beyond the state-of-the-art of conjugated polymers while investigating the gas phase polymerisation of industrial dyes, i.e. DiketoPyrroloPyrrole (DPP) derivatives. In spite of their remarkable properties, including an exceptional light resistance and unique physicochemical properties, conjugated DPP assemblies remain a largely unexplored topic due to the lack of synthetic approaches. The outcomes of the TODAM project are two-fold with i) the development of a oCVD route towards the synthesis, engineering and deposition of unreported non-N-alkylated DPP-based conjugated polymer thin films, and ii) the in-depth study of the photo-electronic and photo-electro-catalytic properties of the new conjugated polymers and the identification of promising building blocks for the preparation of photoanodes and photocathodes for the production of hydrogen from solar-assisted water splitting.
The work performed from the beginning of the project quickly demonstrated that N-unsubstituted DPPs are versatile functional monomers that can be polymerised/copolymerised (oxidative coupling) directly into thin film form via oxidative chemical vapour deposition (oCVD). Initial experiments were conducted using commercially available 3,6-di(2-thienyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (TDPP). TDPP was selected as "model compound" due to the presence of thienyl moieties, which are commonly used in oCVD. Interestingly, grafting of the thienyl group directly to the electron-deficient DPP core did not significantly decrease its electron-rich character, which is crucial for conducting the intermolecular dehydrogenative coupling reaction, and TDPP readily polymerised in oCVD using FeCl3 as oxidant. The influence of deposition conditions (substrate, temperature, pressure, etc.) on the properties of the resulting thin films were studied.
To further investigate the formation of higher oligomeric species, experiments were conducted with alkylated TDPP, i.e. 2,5-bis(2-ethylhexyl)-3,6-di(2-thienyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (BEHTDPP). Following previous solution-based studies, grafting long alkyl chains to the axial positions of the TDPP motif enhanced the solubility of the formed polymeric chains by reducing π-π intermolecular interactions between aromatic systems and preventing hydrogen bonding between amide functional groups. This modification enabled the analysis of formed polymers using GPC (solution-based analysis). The GPC spectrum only displayed a broad peak indicating masses up to 32,000 g·mol-1. Given the similarities in the UV/Vis/NIR and LDI-HRMS spectra of polymerized TDPP and BEHTDPP, it can be assumed that the product of oCVD on TDPP materials also consists of polymeric chains with molecular weights in the range of tens of thousands g·mol-1.
To gain a deeper understanding of the potential of the selected oCVD technique, further studies were conducted on other organic dyes. The strong electron-deficient character of the DPP core hindered polymerization of most DPP derivatives under oCVD conditions. Nevertheless, DPP derivatives substituted with strong electro-donating groups, such as thienyl groups (TDPP and BEHTDPP), were readily polymerised via oCVD and their photo-electronic and photo-electro-catalytic were thoroughly studied. Noteworthy, two-photon photoelectron spectroscopy evidenced that the DPP-based conjugated polymers bearing no N-alkyl substituent exhibits a systematic increase of all lifetimes compared to N-alkylated DPP-based conjugated polymers, notably an increase in the fraction of the very long-lived excited species. The ability to synthesise N-alkylated DPP-based conjugated polymer thin films (only possible using the oCVD approach) and the demonstration of their superior photo-electronic properties is of high interest for photovoltaic applications. Besides, the photo-electronic and photo-electro-catalytic of the conjugated copolymers derived other dyes show remarkable photoactivity.
The results of the TODAM project were already partly disclosed as an open access peer-reviewed research article (M. K. Charyton, T. Reiker, K. Kotwica, M. Góra, H. Zacharias N. D. Boscher Mater. Adv., 2023, https://doi.org/10.1039/D3MA00197K(s’ouvre dans une nouvelle fenêtre)) and via an oral contribution at an international conference (AVS 68th International Symposium & Exhibition 6-11/11/2022 Pittsburgh, USA). Additional open access peer-reviewed publications are currently under preparation. Besides, in the framework of TODAM, the ER and the supervisor established collaboration with multiple universities from Poland, Germany, Austria and Luxembourg and prepared follow-up research proposal applications.
To further investigate the formation of higher oligomeric species, experiments were conducted with alkylated TDPP, i.e. 2,5-bis(2-ethylhexyl)-3,6-di(2-thienyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (BEHTDPP). Following previous solution-based studies, grafting long alkyl chains to the axial positions of the TDPP motif enhanced the solubility of the formed polymeric chains by reducing π-π intermolecular interactions between aromatic systems and preventing hydrogen bonding between amide functional groups. This modification enabled the analysis of formed polymers using GPC (solution-based analysis). The GPC spectrum only displayed a broad peak indicating masses up to 32,000 g·mol-1. Given the similarities in the UV/Vis/NIR and LDI-HRMS spectra of polymerized TDPP and BEHTDPP, it can be assumed that the product of oCVD on TDPP materials also consists of polymeric chains with molecular weights in the range of tens of thousands g·mol-1.
To gain a deeper understanding of the potential of the selected oCVD technique, further studies were conducted on other organic dyes. The strong electron-deficient character of the DPP core hindered polymerization of most DPP derivatives under oCVD conditions. Nevertheless, DPP derivatives substituted with strong electro-donating groups, such as thienyl groups (TDPP and BEHTDPP), were readily polymerised via oCVD and their photo-electronic and photo-electro-catalytic were thoroughly studied. Noteworthy, two-photon photoelectron spectroscopy evidenced that the DPP-based conjugated polymers bearing no N-alkyl substituent exhibits a systematic increase of all lifetimes compared to N-alkylated DPP-based conjugated polymers, notably an increase in the fraction of the very long-lived excited species. The ability to synthesise N-alkylated DPP-based conjugated polymer thin films (only possible using the oCVD approach) and the demonstration of their superior photo-electronic properties is of high interest for photovoltaic applications. Besides, the photo-electronic and photo-electro-catalytic of the conjugated copolymers derived other dyes show remarkable photoactivity.
The results of the TODAM project were already partly disclosed as an open access peer-reviewed research article (M. K. Charyton, T. Reiker, K. Kotwica, M. Góra, H. Zacharias N. D. Boscher Mater. Adv., 2023, https://doi.org/10.1039/D3MA00197K(s’ouvre dans une nouvelle fenêtre)) and via an oral contribution at an international conference (AVS 68th International Symposium & Exhibition 6-11/11/2022 Pittsburgh, USA). Additional open access peer-reviewed publications are currently under preparation. Besides, in the framework of TODAM, the ER and the supervisor established collaboration with multiple universities from Poland, Germany, Austria and Luxembourg and prepared follow-up research proposal applications.
The outcomes of the TODAM project are two-fold with i) the development of a oCVD route towards the synthesis, engineering and deposition of unreported non-N-alkylated DPP-based conjugated polymer thin films (enabling to go far beyond the state of the art of conjugated polymers), and ii) the in-depth study of the photo-electronic and photo-electro-catalytic properties of the new conjugated polymers and the identification of promising building blocks for the preparation of photoanodes and photocathodes for the production of hydrogen from solar-assisted water splitting. The knowledge developed in the framework of TODAM are also foreseen to have a strong impact on the field of photovoltaic.