Clément DIGUET PhD defense

Organometallics: Materials & Catalysis (OMC) team

Abstract
Molecules that possess an intramolecular hydrogen bond can undergo an excited state intramolecular proton transfer (ESIPT), leading to a relaxation of enol form to keto form. ESIPT chromophores are known for their environment-sensitive optical profiles, and a panchromatic emission that can be observed in case of partially frustrated ESIPT. As organic fluorescent compounds, they can be used as emitters in organic light-emitting devices (OLEDs), which are being actively investigated as next-generation. Moreover, the possible dual panchromatic emission of ESIPT fluorophores can make them suitable candidates for the design of white OLEDs (WOLEDs), that are usually made of multiple emitters, whose combination can lead to long-term degradation of light quality and complicate large-scale manufacturing. The third generation of OLEDs, combining 100% theoretical external quantum efficiency and low cost of fabrication, relies on thermally activated delayed fluorescence (TADF). It is a process in which an excited molecule in the triplet state can undergo reverse intersystem crossing (rISC), inducing a return in the singlet state. The aim of this thesis is to design hydroxyaryl-substituted pyrimidine fluorophores which exhibit both ESIPT and TADF. The combination of pyrimidine, as an electron-attracting unit, with bulky and rigid electron-donating groups, such as dimethylacridan, can lead to a twisted intramolecular charge transfer, that can favor rISC process. Synthesis, characterization and investigation of luminescence properties of numerous new fluorophores are described in this manuscript. Hydroxyphenyl pyrimidine compounds are not emissive, but their fluorescence can usualy be restaured in acidic media, leading to strong solvatochromism, which is also exhibited by analogues fluorophores, such as methoxy derivatives or O^N^O boron complexes. One of these complexes shows TADF behavior and has been used in an OLED device, leading to orange electroluminescence with an EQEmax of 11.4%.

Jury
Olivier Siri, CNRS research Director, Université Aix-Marseille
Clémence Allain, CNRS Director, ENS Paris Saclay
Julien Massue, CNRS researcher, Université Strasbourg
Sylvain Achelle, Full Professor, Université Rennes, ISCR
Françoise Robin-le Guen, Full Professor, Université Rennes, ISCR
Sébastien Gauthier, Associate Professor, Université Rennes, ISCR

Contact
Sylvain Achelle, sylvain.achelle@univ-rennes.fr