Development of Novel Hydroporphyrins for Light Harvesting and Sensitising NIR Lanthanide Luminescence

Sammanfattning: Chlorins, as the core structures of chlorophylls, have been extensively studied for harvesting solar energy, fluorescent imaging and photodynamic therapy against cancer. This thesis is concerned with design and synthesis of novel chlorins as antennae for harvesting light and sensitising near infrared lanthanide luminescence.In the first part, a series of chlorin monomers, dimers and polymers were synthesised and their photophysical properties were characterised. The chlorin monomers were substituted with five-membered heterocycles, such as thiophenes and furans. These heterocycles function as auxochromes analogous to the natural ones in chlorophylls, and extend chlorin absorption and emission strongly to the red (up to λem = 680 nm). A borylation method was developed to prepare borylated chlorins, which gave access to directly linked chlorin dimers through Suzuki coupling reaction. Different regioisomers of chlorin dimer were prepared, including β-meso homodimers, meso-meso homodimers and heterodimers. The dimerisation resulted in red-shifted absorption and emission. Chlorin polymerisations were performed both electrochemically and chemically. Bis-thienylchlorins yielded chlorin films and an organic solvent soluble copolymer with hexylthiophene, respectively. These polymers from both polymerisations have red absorptions beyond 700 nm, and might be used as light-harvesting antennae.In the second part, chlorins were used as chromophores to sensitise near infrared lanthanide luminescence. Two types of chlorin-lanthanide dyads were prepared through lanthanide coordination with cyclen derivatives and dipicolinic acids (DPA). The cyclen-based dyads were poorly soluble in water, thus their near infrared emissions were not observed. The other type of complexes was fully soluble in H2O and THF. Both Nd and Yb emission were recorded even upon excitation into the Q bands of chlorins. In the dyads with free base chlorins, the singlet state of chlorins might be involved in the sensitisation of lanthanide luminescence. These DPA-based dyads presented two-color emission based on one chlorin and two-color excitation based on one lanthanide ion. These dyads would enable in theory 4-color imaging.In the last part, a microwave-assisted two-step synthesis was described to prepare dipyrromethanes, which are the key intermediates in the chlorin synthesis. This mild method took advantage of the nucleophilicity of pyrrole and the electrophilicity of N,N-dimethylaminomethyl pyrroles. The usually used acid catalysis is detrimental to many functionalities, thus our methods enable the synthesis of dipyrromethanes with acid sensitive groups or a formyl group.