Molecular and supramolecular strategies for highly luminescent trityl radicals and their sensing applications /

Resumen

Organic radicals are emerging as promising materials in optics and optoelectronics thanks to their open-shell configuration. In this framework, the aim of this Thesis is the development of highly luminescent and photostable trityl radicals. In Chapter I, after an overview on luminescence, the unique optical properties of carbon-centred free-radicals will be introduced, focusing on the strengths and perspectives offered by these molecules in the fields of fluorescence microscopy and electroluminescence devices. In Chapter II, a deep study on the optical properties of the tris(2,4,6-trichlorophenyl)methyl radical (TTM) and perchlorotriphenylmethyl radical (PTM) when used as emitting specie in organic nanoparticles (ONPs) and polymeric films will be presented. Indeed, despite the good knowledge about the luminescence properties of trityl radicals in solution, no systematic studies are reported about the effect of the confinement of radicals in organic rigid matrices. As host systems the optically neutral tris(2,4,6-trichlorophenyl)methane (TTM-αH) and poly(methylmethacrylate) for ONPs and films respectively, have been chosen. Both systems become particularly interesting because for the first time, excimeric emissions from carbon centered free-radicals have been observed due to the formation of stable and persistent supramolecular radical-pairs. Thanks to their emission in the red-NIR region (650-800 nm), these free-radical excimer-forming materials become promising molecular materials for bioimaging and optoelectronics applications In Chapter III, the processes which explain the association and dissociation of the TTM excimers (molecular structure, nature of the host, thermal effects) will be studied. In particular, it has been found that TTM doped ONPs offer the possibility to be employed as cost-effective, ratiometric nanothermometer. In this framework, the ratiometric output of 20% TTM doped ONPs water suspension has been studied in different conditions of polarity, ionic strength and pHs, in order to test its possible applicability as bio thermal sensor. Finally, in Chapter IV the synthesis of the first polybromotriphenylmethyl radical will be presented, i.e. the tris(2,4,6-tribromophenyl)methyl radical (TTBrM). This new molecule constitutes the perfect building block for the synthesis of highly luminescent and photostable trityl radicals. In fact, thanks to its three para bromine functionalizations, this new radical allows to easily overcome the poor synthetic versatility of polychlorotriphenylmethyl radicals opening the way to the easy synthesis of new trityl radical derivatives. Moreover, compared to the analogous chlorinated species, the TTBrM radical exhibits red-shifted absorption and emission, a higher photostability, and it is also able to form NIR-emitting excimers when dispersed in ONPs, constituting a promising radical for bio-imaging applications.