Design and characterization of molecular fluorescent architectures for potential applications as sensors and logic switches

Abstract

The increasing complexity of information technology and the therewith connected demands for miniaturization have alimented the need for alternative small-scale approaches to computing and data processing. Molecules can be one solution for this problem. However, they must be taught to integrate the functions of computing such as logic gates and circuits. Molecular switches can be converted from one state to another by a wide range of external stimuli, such as chemical species, light, temperature etc. This switching action can be translated into binary codes and in some cases (as shown in this thesis) also into multivalued coding. Beside their potential for computing, applications in object coding, intelligent materials, pro¬drug activation, and diagnostics/actuation are widely pursued with molecular switches nowadays. The global objective of this research is to develop new molecular systems, based on molecular logics. Particular attention is given here to aminonaphthalimides and arylisoquinoline dyes with boronic ester groups. The aminonaphthalimide fluorophore, integrated in a receptorrfluorophore-receptor2 architecture, is able to switch its fluorescence upon application of acid input in an off-on-off manner. Thereby the characteristics of a T-latch function are mimicked with a molecular system. Furthermore, a new class of arylisoquinoline fluorophores with boronic ester groups was extensively investigated. The intemal-charge-transfer (ICT) fluorescence emission of these dyes can be fine-tuned in an ample spectral window. These fluorophores can be switched by protonation of the isoquinoline moiety or the formation of fluoroboronate complexes with the boronic acid ester. Borylated arylisoquinoline dyes with pH-dependent fluorescence are also discussed. These dyes feature aromatic amino substitution with appended lateral aliphatic amino groups and the isoquinoline proton receptor. The photophysical properties of the ICT dyes were studied and the fluorescence modulation upon multiple and orthogonal protonation with acid led to the interpretation of multi-level switching including off-on-off, ternary, and quaternary responses.