ALL-OPTICAL CONTROL OF MOLECULAR FUNCTIONS - ENERGY TRANSFER SWITCHING AND INFORMATION PROCESSING

Sammanfattning: In this work, the photoswitching of molecular systems endowed with photochromic functionality have been investigated for the reversible photonic gating of excitation energy transfer (FRET) reactions as well as in application for all-photonic molecular logic. The presented systems involves the integration of photochromic entities within both covalent and non-covalent designs and serves to implicate photonic switching of molecular level phenomena. In particular, all systems include the photochromic modulation of fluorescence emission in response to photonic stimuli. In the first part of this thesis, paper I and II, two different molecular logic systems were designed as to investigate the possibility of using photochromic molecular functions with fluorescent read-out as new possible logic platforms in all-photonic information processing and data storage. In paper I, we present the utilization of a fluorescent photochromic fulgimide derivative in combination with non-linear (SHG/THG) crystals and Nd:YAG lasers for the successful implication of an all-photonic molecular D-flip flop. In paper II, we show the covalent integration of photochromic fulgimide and dithienylethene derivatives into two different photochromic triads, resulting in a “neuron”-like off-on-off fluorescence emission behavior in response to illumination with UV-light, which allowed the implication of an all-photonic molecular parity generator/checker. In the second part, papers III and VI, the possibilty for using photochromic compounds in the construction of photoresponsive supramolecular assemblies was explored. In paper III, we show the reversible photoswitching of excitation energy transfer between a donor-acceptor (FRET) pair appended to a DNA-template by photochromic modulation of the DNA-binding properties of an amidine-substituted spiropyran derivative. In paper IV, we show dichromatic emission color-tuning and generation of virtually perfect white light fluorescence by regulation of FRET communication between a donor fluorophore and a fluorescent photoswitch encapsulated in polymer micelles.