Sythesis Of Organic Triplet Photosensitizers And The Investigations On Photophysical Property

Triplet photosensitizers (PSs) have attracted much attention due to their special photophysical and photochemistry properties. Triplet PSs are used for photodynamic therapy (PDT), photoinduced hydrogen production from water and triplet-triplet annihilation (TTA) upconversion, photocatalytic organic reactions and oxygen sensing. Traditional triplet (PSs) are mainly transition metal complexes. The small molar absorption coefficients in the visible spectral region and short-lived triplet excited states limit the applications of these complexes. It is trimendously important to develop new triplet PSs, especially organic compounds without any heavy atoms, in order to replace the conventional transition metal complex triplet photosensitizers which are not economic, not environment benign.This thesis will design and synthesis organic triplet PSs that are without any heavy atoms. Experiments and DFT calculations were combined for the study of the photophysical and photochemical properties of these heavy atom-free organic triplet photosensitizers.Herein, a series of new fluorophores with a fused coumarin framework were prepared. The dyes show red-shifted and enhanced absorption compared to the reference compound. Based on DFT calculation we found that the fused coumarin undergo significant geometry relaxation upon photoexcitation, which is responsible for their large Stokes shifts. Population of the triplet excited state was observed for the bromo-functionalized coumarin. In order to study the triplet state of organic dye coumarin, we synthesis a series of ketocoumarin compounds as heavy atom-free triplet photosensitizers that with intramolecular nâ†'Ï€*transition. The photophysical properties of the compounds were studied with steady state and time-resolved spectroscopy and DFT calculation. The compounds show absorption in visible spectral region and long-lived triplet excited states.these compounds were used as triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion.In order to prepare triplet PSs which show longer absorption wavelength, BODIPY chromophore was selected as light harvest antenna, and fullerene (C60) was used as intramolecular singlet energy acceptor and at the same time, the spin converter. C60-BODIPY dyads (C-10and C-11) were prepared as heavy-atom-free organic triplet (PSs) for TTA based upconversion. Furthermore, we report a strategy to enhance the visible light-absorption capbility of triplet (PSs) by multi-intramolecular energy transfer-induced broadband absorption of visible light, we prepared a Coumarin-BODIPY-C60triad as heavy atom-free triplet (PSs) with two visible light-harvesting moieties of coumarin and BODIPY, C-12and the reference compounds C-13, C-14which are only with one light-harvesting moiety. Combined with DFT calculation, the steady state and time-resolved spectroscopy, we concluded that energy transfer from the antennas to the energy acceptor C60is very efficient (up to97%). The long-lived triplet excited state are localized on the C60part rather than the light-harvesting antenna. The C60dyads/triad were used as triplet photosensitizers for photooxidation of DHN and TTA upconversion. Significant TTA upconversion was also observed with the triad. For both the oxidation rate and product yields, the singlet oxygen (1O2) sensitizing of the triad is more efficient than the dyads, and stronger than the reported compound tetraphenyl porphyrin (TPP).