Synthesis of multichromophoric calix[4]arene-based systems for the investigation of energy and charge flow

Abstract

The work presented in this thesis describes the synthesis and the spectroscopic characterization of chromophore-equipped calix[4]arenes designed for two different purposes: the development of bichromophoric model systems for the investigation of photoinduced energy and electron transfer processes, and the preparation of antenna ligands for the sensitization of lanthanoid ions. The calix[4]arene represents a versatile scaffold that can be functionalized with several chromophores and ligating units, can adopt different conformations, offering control over the distance and reciprocal orientation of the dyes, and is endowed of a residual flexibility that can be modulated according to the medium. After an introductory chapter, the second chapter describes the synthesis of a bichromophoric dyad obtained by anchoring a Nile Red dye and a fullerene C60 on the upper rim of a cone calix[4]arene and the steady-state spectroscopic studies aimed at investigating the energy and charge transfer phenomena occurring after photoexcitation of Nile Red. In the third chapter is reported the functionalization of a cone and a 1,3-alternate calix[4]arene with two different BODIPY dyes specifically selected to study the occurrence of coherent phenomena in the energy transfer process. The use of different conformations of the scaffold allowed us to investigate the influence of the interchromophore distance on the transfer efficiency. The fourth chapter deals with the exploration of synthetic pathways to obtain a small library of calix[4]arene-based antenna ligands for the photosensitization of lanthanoid ions. The library was designed with the aim of analyzing the role of different factors, such as the antenna structure, the distance between the antenna and the lanthanoid and the number of antennae, on the efficiency of the sensitization. Three different antennae, absorbing in the UV and visible region, were thus synthesized to be linked either at the upper or at the lower rim of three different calix[4]arene scaffolds. One of them is a redox-reversible antenna that can be exploited to investigate the potential of on-off switching of lanthanoid luminescence.