Shushen CHI PhD defense
Synthesis and properties of porphyrins decorated with accepting groups
Thursday 12 February, 10:00Passed
Organic Chemistry & Interfaces (COrInt) team
Abstract
During this thesis, we have focused on the design, synthesis, and photophysical properties of several series of meso-tetrafluorenylporphyrin (TFP) derivatives bearing π-extended antenna units connected through ethynyl or vinyl bridges. By systematically varying the terminal electron-withdrawing substituents strength (EWGs: -CHO, -NO2, -SO2CF3, -Py, -Py +) on the four antennas, the work establishes how structural modifications aƯect both linear (LO) and nonlinear optical (NLO) properties, with particular focus on their luminescence, two-photon absorption properties (2PA) and singlet oxygen formation. In the first chapter, we present the general background of the porphyrin chemistry. It introduces their structure, synthetic methods, and photophysical properties, especially applications in two-photon photodynamic therapy (2P PDT). We further reviewed prior porphyrin studies done in our group and proposed new molecular designs based on these results. From Chapters 2 to 4, we focus on ethynyl-linked TFP porphyrins, in which the electronic character of the terminal groups was tuned according to their Hammett constants by introducing EWGs with increasing strength. For each of this substituent, small, medium, and large π-extended architectures were prepared using alkynyl linkers, and an additional prolonged analogue was synthesized for the last series (-SO2CF3). Comparative optical studies across these diƯerent families show that stronger EWGs promote more eƯicient intramolecular charge transfer (ICT) and antenna- to-core energy transfer (ET), and they also lead to clear enhancements in 2PA. In Chapter 5, we examine a structurally distinct system: the TFP porphyrin functionalized with 4- pyridyl (4-Py). The water solubility can be modulated by adjusting the strength of the terminal EWG. The 4-Py is connected via an ethynyl spacer, enabling electronic eƯects to be tuned without directly perturbing the conjugated manifold. Upon methylation, the resulting pyridinium substituent (4-Py + ) exhibits stronger electron-withdrawing character, leading to improved photophysical performances, including higher 2PA. Together with its tunable aqueous solubility, this system shows promising potential for 2P PDT. Finally, for the last chapter, we describe the synthesis and characterization of a series of ethylene-bridged fluorenyl- vinylene porphyrins and their Zn (II) complexes, incorporating terminal groups of varying electron-withdrawing strength used previously. Optical studies reveal that, for the free porphyrin, despite reduced rigidity relative to the ethynyl analogues, these vinyl-linked systems maintain eƯicient ET and strong singlet-oxygen generation, with many members displaying higher 2PA cross sections attributable to increased polarizability. For the Zn (II) complexes, metal coordination modifies molecular symmetry and electron distribution, oƯering another means of tuning optical properties. Their 2PA trends follow those of the corresponding free-base porphyrins.
Jury
Gilles LERMERCIER, Professeur des Universités - Université de Reims Champagne-Ardenne
Duncan CARMICHAEL, Chargé de Recherche CNRS (HDR) - Ecole Polytechnique Paris
Olivier MONGIN, Université de Rennes, ISCR / Co-supervisor
Christine PAUL-ROTH, INSA Rennes, ISCR / Supervisor
Contact
Christine Paul-Roth, christine.paul@univ-rennes.fr
