Syntheses And Applications Of Novel Organic Triplet Photosensitizers Based On Bodipy And NDI Derivatives

Organic triplet photosensitizers (PSs) have attracted much attention due to their wide use in triplet-triplet annihilation (TTA) upconversion and photocatalysis. Conventional triplet PSs include halogenated xanthanes such as Rose Bengal and methylene blue, and transition metal complexes such as Pt(?), Ru(?) or Ir(?) complexes, etc. These triplet PSs suffer from drawbacks, and the application is limited. The drawbacks include the dependence on noble metal atoms, weak and narrow absorption band, short triplet state lifetime, and unpredetermined intersystem crossing (ISC) property, etc. In an attempt to address these drawbacks, series of new organic triplet PSs, i.e. halogenated compounds and C60-chromophore dyads, were developed in this thesis.Firstly, bromo-substituted NDI (3-1?3-6) were prepared as metal free triplet PSs. The redshift of absorption of 2,6- or 2,3,6,7-tetrabromo substituents NDI derivatives were achieved by attachment of amino substituents. The triplet excited state lifetime of 3-5 was determined as 51.4?s, and its TTA upconversion quantum yield was up to 18.5%. In addition, the rate of photooxidation with 3-5 as PS was 6-7 times faster than Ir-1. It should be noted that 3-5 was a non-recycled photocatalyst. In order to address this drawback, we prepared porous silica-immobilized iodo-Bodipy(material 3-7) as an efficient recyclable photocatalyst for photoredox catalytic tandem oxidation/[3+2] cycloaddition reactions of tetrahydroisoquinoline with N-phenylmaleimides to prepare pyrrolo[2,1-a]isoquinoline.3-7 showed a good tolerance for different substrates (isolated yield:51-80%). The photocatalyst was readily recovered with a centrifuge and was re-used for photocatalysis. The yield did not decrease significantly after three recycles.Secondly, resonance energy transfer (RET) was used to enhance the light absorption in triad triplet PSs to access strong and broadband absorption in visible region (450 nm-750 nm). This strategy was demonstrated by preparation of (Bodipy)2-diiodo-Aza-Bodipy triad (4-2) and (carbazole-styryl Bodipy)2-diiodo-Aza-Bodipy triad (4-3), in which the energy donor (Bodipy or styryl-Bodipy) and the energy acceptor (aza-Bodipy, also as the spin converter) parts were connected by click chemistry. Intramolecular energy transfer process for these Bodipy hybrids was observed, and the triplet excited states of both 4-2 and 4-3 were localized on the iodo-aza-Bodipy part. The rate of photooxidation for 4-2 was 7 times faster than Ir-1. Furthermore,4-2 and 4-3 were used as photocatalysts for photoredox catalytic tandem oxidation/[3+2] cycloaddition reactions and the Cu(?) catalyzed alkynylation reactions, respectively. Photocatalytic ability of the new triplet PSs are more efficient than conventional photocatalysts such as [Ru(bpy)3]Cl2.At last, C60-Bodipy dyads were prepared (5-1-5-3) as heavy atom free organic triplet PSs with a predictable photophysical properties. Nanosecond time-resolved transient absorption spectroscopy indicated that the triplet excited state of the dyads were localized on C6o part for 5-1 and styrylBodipy part for 5-2 and 5-3, respectively. An intramolecular "ping-pong" energy transfer process was observed for 5-2 and 5-3. C6o-Bodipy dyads were used for TTA upconversion, and the upconversion quantum yield of 5-2 was up to 9.1%. Moreover, supramolecular triplet PSs based on hydrogen bonding-mediated molecular assemblies were prepared. Three thymine-containing visible light-harvesting Bodipy derivatives (5-8,5-9 and 5-10, which showed absorption at 505 nm,630 nm and 593 nm, respectively) were used as H-bonding modules, and 1,6-diaminopyridine-appended C60 was used as the complementary H-bonding module (5-7), in which the C60 part acted as a spin converter for triplet formation. Singlet/triplet energy transfer process was regulated by H-bonding. The nanosecond transient absorption spectroscopy showed that the triplet state was localized on the C6o module for assembly 5-7/5-8, and on the styrylBodipy antenna for assemblies 5-7/5-9 and 5-7/5-10 through an intra-assembly "ping-pong" energy transfer process, respectively. These supramolecular assemblies were used as triplet PSs for TTA upconversion.