Diseño y caracterización de nuevos sistemas fluorescentes para su utilización como interruptores y puertas lógicas molecularesimplicación de procesos de transferencia electrónica y de energía en el estado excitado

Abstract

The investigation of photoactive and/or fluorescent molecular switches is a field of chemical research with intensive worldwide activities. This doctoral thesis contributes to these activities with the design and characterization of new molecular switches and model systems that can be used to study energy transfer processes. In detail works in three thematic blocks have been realized: (i) use of supramolecular chemistry for the realization of reversible and resettable logic functions in water, (ii) implementation of photochromic compounds as central units of switches with the capacity of sequential molecular logic (molecular keypad locks and memory switches), and (iii) investigation of energy transfer processes with fullerene- or BODIPY-containing molecular dyads and their potential application in photovoltaics and for bioimaging of cellular structures. An host-guest complex between the cucurbit[7]uril organic macrocycle and a pH-dependent fluorescent naphthalimide-benzimidazole guest were used to demonstrate the macrocycle-induced control of photoinduced electron transfer of the guest. The resulting input-dependent fluorescence signal was applied for the demonstration of supramolecular logic operations including INHIBIT, AND or NOR. As an additional advantage the logic functions can be reset and reconfigured, which makes the system a versatile platform for molecular information processing. All operations were done in water and can be potentially applied in biomimetic contexts. Photochromic molecular switches (fluorophore-appended spiropyrans and a fulgimide) that can deliver distinct fluorescence responses depending on their ring-open and ring-closed states were investigated. Based on the detailed photochemical and photophysical characterization a molecular keypad lock and a D-latch memory device were developed and demonstrated. These rarely reported molecular logic devices depend not only on the aDolication of the �riaht� inDut information (chemical sDecies or liaht inDuts of varvina wavelenathsV but also on the relative order of the input application. Such switches are not trivial and the developed research is without doubt at the frontline of these recent developments in molecular information processing. Some of the mentioned photochromic switches rely on energy transfer as excited state process. There is a constant interest of using energy transfer as design principle for molecular dyads with the most diverse functions. Herein several aminonaphthalimide-fullerene dyads were investigated and quantitative energy transfer was shown. Thus, the systems emulate antenna functions where the excitation energy is canalized to the fullerene (C60 or C70). These allotropic carbon forms have found much attention for their use in photovoltaic systems and in this context the undertaken studies provide interesting mechanistic and photophysical insights that are combined with a potential for applications. The other type of energy transfer dyads used again an aminonaphthalimide as energy donor and a BODIPY dye as acceptor. This class of dyes finds widespread use as sensors and probes in bio-related research, among them fluorescence confocal microscopy imaging. In order to increase the inherently small Stokes shift of the BODIPY dye an antenna chromophore can be used that transfers its excitation energy to the acceptor dye. In this thesis it was shown that highly efficient energy transfer can be observed in the investigated aminonaphthalimide-BODIPY dyads. As a special twist the energy transfer works not only under conditions of one-photon excitation but also in the non-linear two-photon absorption regime. This extends the application potential of BODIPY dyes in bioimaging tremendously. In a model study this has been demonstrated for the imaging of HeLa cells. In global statement it can be summarized that in the presented thesis that the control of excited state processes such as photoinduced electron transfer and energy transfer can be used for a wide spectrum of applications ranging from molecular information processing to photovoltaics and bioimaging.