Triplet harvesting of gold(I) supramolecular complexes and their applications

[eng] This thesis has been done under the supervision of Prof. Laura Rodríguez (Inorganic Chemistry Section, Universitat de Barcelona) and Prof. João Carlos Lima (LAQV REQUIMTE, Universidade Nova de Lisboa). Over these four years, several gold(I) organometallic complexes with different structural characteristics have been synthesized. The compounds present different nuclearities (number of metal atoms) and different chromophores and ancillary ligands. The different parts of the molecules play a direct influence on their resulting luminescent properties. Since gold(I) displays a linear geometry, the chromophores have been coordinated in one of these positions, in the other one, different phosphanes, and diphosphanes as ancillary ligands. The main aim of this Doctoral Thesis is to study the luminescent properties and photophysics of these compounds in order to deeply understand how to efficiently promote the harvesting of triplet excited states, Tn, which are those responsible for the resulting phosphorescence emission, in order to obtain room temperature phosphorescence materials (RTP). Other applications have been explored, such as sensing water pollutants and singlet oxygen production. The interest in preparing compounds suitable for RTP materials relies on the fact that when producing excitons through electricity, 25% of them populate the Sn states, while 75% of them harvest the Tn instead. The forbidden character of the triplet excited state and its lower energy favours non-radiative decays. Hence, the use of an efficient way to obtain luminescent materials with high phosphorescence quantum yield is a challenge. On the other hand, the high sensitivity of luminescence is of great relevance to be used to prepare luminescent chemosensors. The use of phosphorescence sensors can help detect other types of contaminants that present intrinsic fluorescence emission that appears at shorter wavelengths. Finally, the production of singlet oxygen has been widely studied in the last years, with great potential in several research fields, such as photodynamic therapy (promoting the formation of ROS species that can attack carcinogenic cells) or catalytic reactions (using the singlet oxygen specie as a green catalyst). The advantage is that singlet oxygen is generated from oxygen, O2, which is very abundant in our atmosphere and can be produced through energy transfer from triplet excited states of molecular sensitizer, leading to the quenching of these states. This energy transfer can take place because the ground state of the O2 is a triplet, which permits the simultaneous transition of both triplets (molecular sensitizer and dioxygen) to the singlet state (excited singlet state of dioxygen and ground singlet state of the molecular sensitizer). Compounds with heavy atoms in their chemical structure, that can have populated the triplet excited state, are good molecular sensitizers, favouring the production of singlet oxygen instead of giving rise to phosphorescence emission. This PhD thesis is divided in different chapters that contain different families of gold(I) complexes displaying diverse structures. The presence of the gold(I) metal unit is crucial for promoting what is called “heavy atom effect”, which induces the promotion of the population of Tn states. The phosphanes and diphosphanes used have been crucial to modulate their solubilities and, also, the intra- and intermolecular supramolecular interactions present in the complexes. These interactions can modify the luminescent properties that the compounds present. Not only π···π and C-H···π interactions can be promoted, but also the so-called aurophilic contacts. Different characterization techniques have been used to evidence the pure formation of the organic and organometallic molecules (1H and 31P NMR, IR, ESI, MALDI-TOF, and DRX). Their luminescent properties have been analysed through Uv-Vis absorption and emission spectra under different conditions such as air-equilibrated, N2-saturated, solid, low temperature, and immobilized into organic polymeric matrices. Their luminescence lifetimes and quantum yields have been also measured. All these characterization techniques have been done in our groups’ facilities at the University of Barcelona. Several photophysical characterization require the use of the laser flash photolysis equipment, and these measurements have been done at the Universidade Nova de Lisboa facilities at the LAQV@REQUIMTE (CHARM group), during a short stage period. These measurements have been crucial for this work since it helped us to calculate the quantum yields of the formation of the triplet excited states (φT). All in all, we have tried to give a bit of light on the analysis of the photophysical parameters of gold(I) complexes, mainly regarding the effects that can affect the triplet harvesting and resulting derived properties (room temperature phosphorescence vs singlet oxygen production).