Tuning The Excited State Of Dyes Via Electron Transfer And Its Application

Triplet photosensitizers have been applied in photocatalysis,oxygen sensing and triplet-triplet annihilation(TTA)upconversion based on triplet-triplet energy transfer.Lots of research has shown that there is competition between electron transfer and energy transfer.The competition constrains the efficicency of triplet energy transfer to a certain extent.For these reasons,tuning the intramolecular electron transfer can not only strengthen the efficiency of triplet energy transfer effectively,but also can regulate the intensity of fluorescence flexibly.The main contents of this research are as follows.1.Six coordinated Pt(?)complexes were prepared,in which the C*N^N or the C^N^N ligand were used to form the Pt(?)coordination center.For each coordination profile,three different arylacetylide ligands were used.The electrochemical and the photophysical properties of the complexes were studied with steady-state and time-resolved absorption,emission spectroscopy,cyclic voltammetry and DFT calculations.It is the first time that the Rehm–Weller Equation was used to further investigate the charge transfer process(MLCT),and the thermodynamic driving forces for the charge transfer process(?G°,free energy change of the potential charge transfer)were calculated based on the redox potential values.along with the competition between electron transfer and energy transfer and the energy level of ligand is matching with the excited state of MLCT of transition metal complex.We predicted correctly the property of triplet excited state of transition metal complex efficiency.The photostability and the photoluminescent properties of the complexes are finely tuned by the photoredox and photochemical properties of the arylacetylide ligands and C*N^N/C^N^N Pt(?)coordination center.The triplet excited states of the complexes are in intraligand feature and the lifetime is long.The complexes were used as triplet photosensitizer for triplet-triplet annihilation upconversion,the upconversion quantum yield is up to 29.7 %.2.Different linkers were used in these two dyads for connection of the BODIPY and the Fc moieties together,The photophysical properties of the dyads were studied with stead-state UV-vis absorption spectroscopy,fluorescence spectroscopy,electrochemical characterization,time-resolved fluorescence and nanosecond transient absorption spectroscopies.The fluorescence of the BODIPY moieties in FcB-1 and FcB-3 was quenched significantly,due to the photo-induced electron transfer(PET)mechanism.This conclusion was supported by electrochemical characterization and calculation of the Gibbs free energy changes of PET.The fluorescence of the BODIPY moiety can be reversibly switched ON and OFF by chronoamperometry and the fluorescence emission corresponds to over 80% of the fluorescence intensity of BODIPY chromophore.This result is much higher than previously reported 33.2%.Furthermore,we proved that the Fc moiety is efficient for quenching of the triplet excited state of BODIPY.Two quenching mechanisms,PET and Triplet-triplet-energy transfer(TTET),are responsible for the intramolecular and intermolecular quenching of the triplet excited state of the diiodoBodipy unit.