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Computational studies on materials for organic light-emitting diodes (OLEDs)

Periodic Reporting for period 1 - CompOLEDs (Computational studies on materials for organic light-emitting diodes (OLEDs))

Reporting period: 2016-11-01 to 2018-10-31

Producing light with low energy consumption and low production costs is of vital importance for the lighting industry and also to face major societal challenges, i.e. exploiting energy resources more efficiently. Towards these aims, organic light-emitting diodes (OLEDs) are excellent candidates. This research project, CompOLEDs, aimed at the refined understanding, at a molecular level, of the photochemical processes occurring in transition metal (TM) complexes and organic dyes used as phosphors and fluorophores in OLEDs. Hence, the computation of the i) photophysical properties, ii) steady-state and dynamic properties and iii) reliable potential energy surfaces, which are mandatory to get insights into the processes occurring after light excitation, have been performed during this MSCA action. The design of photoactive materials with tailored photochemical properties is very often done in a trial-and-error manner. Instead, accurate predictive tools would be highly desirable. Thus, in CompOLEDs we have addressed current key challenges in OLEDs design, including: i) how to improve the internal and external photoluminescence efficiency and ii) how to fine-tune the emission color, notably to achieve white OLEDs (WOLEDs) and highly-efficient photostable blue emitters. Finally, close collaborative work with experimental partners, which consisted of synthesizing and characterizing phosphors and TADF emitters, were also performed during this research program.
During the 1st year of CompOLEDs the focus was put on organometallic complexes. Importantly, the computational protocols along with the advanced phenomenological models developed have permitted to unveil the origins of relevant degradation mechanism upon OLEDs operation, and to develop photostable blue phosphor design strategies (DOI: 10.1039/C7SC03905K). During the 2nd year of CompOLEDs both phosphors and TADF emitters for OLEDs have been investigated. Importantly, the first general computational protocol to compute phosphorescent OLED efficiency (DOI: 10.1021/acs.jpcc.8b00831) resulted from this latter period of CompOLEDs. The studies on other luminescent molecular systems and on TADF emitters were also performed during the 2nd year, leading to additional publications as listed below. Publications: We have published 12 peer-reviewed publications during CompOLEDs (DOIs: 10.1021/acs.inorgchem.7b01692; 10.1002/chem.201703273; 10.1021/acs.jpcc.7b06714; 10.1021/acs.jpclett.7b00015; 10.1039/C7SC03905K and 10.1039/C6DT04414J 10.1021/acs.jpcc.8b00831; 10.1039/C8CP01101J; 10.1039/C8CC02104J; 10.1021/acsaem.8b00732; 10.1002/ejoc.201701724; 10.1021/acs.inorgchem.8b01675). Among those, 6 correspond to the project publications, strictly belonging to CompOLEDs, and we have in addition published other 6 publications not strictly belonging to the CompOLEDs project. Importantly, the 6 project publications were made open-access. Notably, these results have been published in both specialized and broad general chemistry international journals, including high-impact ones (i.e. Chemical Science). Conference, workshop attendance, courses, and /or seminar presentations: During the 1st year of CompOLEDs, we disseminated the early-stage results at international conferences on organic electronics, photochemistry and computational chemistry. More in details, invited/contributed oral communications have been presented at the International Conference of Photochemistry (Strasbourg, ICP 2017, http://icp2017strasbourg.u-strasbg.fr) at the CECAM workshop on modelling organic electronics (Grenoble, https://www.cecam.org/workshop-2-1383.html) at the International Symposium on Molecular Design of Opto-electronic Materials (Beijing, http://www.shuaigroup.net/index.php/news/58) and at the Materials Research Conference 2017 Thailand (Chiang Mai, http://www.mrs-thailand2017.science.cmu.ac.th). Additionally, a poster communication was presented at the WATOC 2017 International Conference (Munich, http://www.watoc2017.com). These academic activities were complemented with intersectorial activities. Notably, a seminar at Samsung Advanced Institute of Technology, (Moscow, Russia, Feb. 2017) was performed. During the 2nd year of CompOLEDs, we disseminated the results at international conferences on organic electronics, photochemistry and computational chemistry. More in details, an invited/contributed oral communications was presented at the 6th Molcas Developers Workshop (Leuven, Belgium; https://quantchem.kuleuven.be/mdw6/program.html) and at the Molecular Engineering and Computational Modelling for Nano- and Biotechnology: From Nanoelectronics to Biopolymers Conference (Cherkasy, Ukraine; https://sites.google.com/view/mecm2018/home). Additionally, a poster communication was presented at the PhotoIUPAC conference (Dublin, Ireland; http://photoiupac2018.com). These academic activities were complemented with additional seminars at renowned institutions (i.e. at the Southern California University, USA (hosted by Prof. M. E. Thompson) and at the City University Hong Kong, Hong Kong (hosted by Prof. Yun Chi).
"Progress beyond the state of the art and scientific and socio-economic impacts of CompOLEDs: Two major scientific outcomes, which go beyond the state-of-the-art in the field of modeling OLEDs, have been derived from CompOLEDs: The first one, in the framework of the collaboration in the field of excited state decay rate formalisms with the group of Prof. Shuai, (Tsinghua University, China), we have provided the first evidence that OLED efficiencies can be modelled at the first principles level. Our approach is based on the combination of state-of-the-art quantum chemical calculations and excited-state decay rate formalism with kinetic modeling, which is shown to be an efficient and reliable approach for a broad palette of Ir(III) complexes, i.e. from yellow/orange to deep-blue emitters. Due to the enormous industrial efforts in obtaining highly-efficient phosphors and the increased use of high-throughput approaches on computational materials’ design, we anticipate that this protocol will be of great importance for the automatic in silico prescreening of promising OLEDs materials. These results led to an important publication at the framework of CompOLEDs (DOI: 10.1021/acs.jpcc.8b00831) which is already cited 11 times and has already acquired the status of ""Very Important Paper"" in Web of Knowledge, despite being a 2018-paper. The second one concerns the computational protocols along with the advanced phenomenological models developed, which have permitted to unveil the origins of relevant degradation mechanism upon OLEDs operation, and to develop photostable blue phosphor design strategies. These results led to a publication at the high-impact general chemistry journal Chemical Science (DOI: 10.1039/C7SC03905K; open access). Further impacts: Concerning the career development of the MSCA fellow, the long-term career objectives have been accomplished. Hence, the MSCA fellow reached a strengthened position in the field of computational photochemistry and succeeded attaining a tenure-track position as assistant professor at the KU Leuven, which it is among the top universities in Europe.

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