Design And Properties Of Novellodo-Pyrrole-BF₂ Triplet State Photosensitizers

Organic triplet state photosensitizers have attracted much attention due to their applications in photo-dynamic therapy, photocatalysis and triplet-triplet annihilation upconversion, etc. However, traditional triplet state photosensitizers have disadvantages as follow:(1) The photosensitizers have only one chromophore, thus, the broadband visible light harvesting is inefficient; (2) The molecular structure is difficult to be modified or be rationally designed. In order to solve these problems, resonance energy transfer and photoinduced electron transfer were used to design iodo-pyrrole-BF2 organic triplet state photosensitizers. New type symmetric bispyrrole-BF2 chromophore (BOPHY) was also used to design iodo-bispyrrole-BF2 organic triplet state photosensitizers. Photophysical properties of the photosensitizers were studied and the photosensitizers were used in applications of photooxidation and triplet-triplet annihilation upconversion experiments.Pyrrole-BF2-based chromophore (Bodipy) has a higher molar extinction coefficient and fluorescence quantum yield in visible region. Thus, Bodipy was used to synthesize multi-chromophore organic triplet state photosensitizers with broadband absorption. Photophysical properties demonstrate that a "ping-pang" type energy transfer exists in these photosensitizers. Nanosecond time-resolved transient absorption spectra demonstrate that triplet state populated on energy donor and acceptor. DFT calculation indicated the energy level of T1 and T2 states is identically. All the photosensitizers were applied to photooxidation and triplet-triplet annihilation upconversion research. New type photosensitizers with broadband absorption in visible region have higher upconversion quantum yield and larger photooxidation rate constant than the traditional mono-chromophore triplet state photosensitizers.2,4-dinitrobenzenenesulfonyl (DNBS)-caged diiodoBodipy organic triplet photosensitizers were designed and synthesized. Photoinduced electron transfer (PET) process can quench the singlet state but can't quench the triplet state of the chromophores. In polar solvent such as CH3CN, as the addition of thios, the triplet state life time extended from 24.7 us to 86.0 ?s. The singlet state quantum yield changed from 88.6% to 92.5%. The upconversion quantum yield increased from 0.2% to 0.5% and the single oxygen quantum yield increased form 74% to 88%. DNBS-caged Bodipy was used as upconversion acceptor in TTA upconversion, no upconversion emission was observed before and after addition of thiols. Calculation of the Gibbs free energy changes of the electron transfer indicates that the electron transfer is efficient in polar solvent such as CH3CN when the DNBS-diiodoBodipy is in singlet state.A series of diiodoBOPHY organic triplet state photosensitizers were designed and synthesized based on new type symmetric pyrrole-BF2 chromophore (BOPHY). The steady/ transient-state spectra and DFT calculation were used to study the photophysical properties. Triplet state quantum yield and singlet oxygen quantum yield were compared with traditional diiodoBodipy photosensitizers. In the study of intermolecular triplet energy transfer, T1 state energy level of new diiodoBOPHY photosensitizer was found higher than traditional Bodipy chromophore. New photosensitizers were also used in TTA upconversion study and the upconversion quantum yield was determined as 2.8% for diiodoBOPHY (D-1). These results will provide experimental basis for design new type triplet photosensitizers.