Search

Asymmetrically substituted zinc phthalocyanine (Pc) derivatives bearing quaternized triazolyl moieties for water solubility and iodine as a heavy metal atom have been investigated as singlet oxygen generators in aqueous media. In addition to the heavy atom effect exerted by iodine covalently bonded to the Pc molecule, a second dimensional effect induced by aggregation which brings the iodine anions of triazolyl units into closer proximity to the Pc core leading to the highest reported singlet oxygen generation for a Pc derivative in water ( Φ Δ = 0.87).

To test the tunability of charge transfer (CT)-based BODIPY photosensitizers in generating singlet oxygen (1Δg), twelve meso-phenyl-BODIPY (donor-acceptor) type compounds have been synthesized and fully characterized, in which the phenyl moiety is modified with respective 0, 1, 2 and 3 methoxy groups to increase its electron-donating ability. The UV-Vis absorption spectra, fluorescence emission spectra, fluorescence quantum yield, fluorescence lifetime, excited triplet state formation, and singlet oxygen formation properties are measured. DFT quantum chemical computation is also carried out to explain the experiments. The occurrence of intra-molecular CT is confirmed by UV-Vis absorption, fluorescence properties and quantum chemical computation. The triplet excited state formation is evidenced by laser flash photolysis technique. The quantitative photosensitized singlet oxygen formation is demonstrated by DPBF (diphenylisobenzofuran) chemical trapping method. This type of BODIPY CT photosensitizers show good tunability in generating singlet oxygen (1Δg). When the number of methoxy group on the donor is increased (so that CT is enhanced), the efficiency of singlet oxygen generation becomes higher from 0.070 to 0.30. When solvent polarity is increased (CT is also enhanced), the efficiency of singlet oxygen generation is also increased significantly. The increase in singlet oxygen generation is accompanied by the decrease in fluorescence quantum yield and fluorescence lifetime values. These facts show that a higher CT efficiency in a simple phenyl-BODIPY donor-acceptor conjugate can lead to significant higher quantum yield of singlet oxygen generation. These results are useful in designing novel CT-based heavy-atom-free photosensitizers for photodynamic therapy of tumor.

An easily prepared, cost-effective and solution processable tetraphenoxy substituted phosphorous triazatetrabenzo corrole (PVTBC) was synthesized and tested as the hole transporting material (HTM) for MAPbI3 perovskite solar cells (PSC). This phthalocyanine analogue HTM works efficiently in the absence of any dopant or additive for the device composed of FTO/c-TiO2/m-TiO2/MAPbI3/HTM/Au. The optimized undoped mesoscopic solar cell device based on the PVTBC compound exhibited a good power conversion efficiency (PCE) of 16.1% (measured at 100 mW cm2 illumination, AM 1.5G), together with a good long-term stability under ambient conditions, in contrast to the PCE of 11.2% for Spiro-OMeTAD under the same condition. This result paves the way for further developing TBC as a new type of low cost HTMs.

Four covalent BODIPY hetero-dimers, formed by different linking positions at (2,2′), (2,8′), (3,8′) and (8,8′) respectively, were designed and synthesized to compare their ability for excited triplet state (T1) and singlet oxygen generation. In contrast to BODIPY monomers that show negligible photosensitizing ability, the four dimers are very efficient for T1 and singlet oxygen formation depending on the individual linking style and solvent polarity. Laser flash photolysis, time-resolved/steady state fluorescence, quantum chemical calculation and thermodynamic analysis revealed that the mechanism of triplet state T1 formation is different from the traditional intersystem crossing mechanism. The T1 formation is due to charge recombination of the twisted charge separation state (TCSS), while the TCSS is generated by photoinduced intramolecular charge transfer (PCT) from one BODIPY monomer moiety to another within the dimer. The PCT based photosensitizers are also medium polarity sensitive which may be very useful in designing and synthesizing of photosensitizers for photodynamic therapy of tumor, photobiology and organic photochemistry.

We have synthesized tetra(4-tert-butyl phenoxy)-tetrabenzocorrolazine phosphorous POTBC(β-OPB)4, a functional π-conjugated macrocycle compound derived from corrole or corrolazine, by a one step procedure from its metal free phthalocyanine precursor. The product structure is characterized by UV–Vis absorption, MS, NMR and IR spectral methods. We have also studied their fluorescence properties, excited triplet state formation, photosensitized singlet oxygen production, and their application as undoped hole transporting layer (HTL) in perovskite solar cells (PSC). The results show that POTBC(β-OPB)4 is highly emissive (fluorescence quantum yield 0.60 in the red region which is little affected by solvent), it also exhibits significant singlet oxygen formation ability (quantum yield 0.40 which is little influenced by solvent), and show remarkable power conversion efficiency (15.8%) as undoped HTL. These facts suggest that POTBC(β-OPB)4 is a promising fluorescence imaging agent and good singlet oxygen photosensitizer for photodynamic therapy of tumor. It is also a good candidate as undoped hole transporting material for PSC.

Nanoscaled rhodamine (NSR) dyes were prepared by reprecipitation method and characterized by TEM and laser diffraction analysis. The optical properties of nano wired rhodamine dyes were studied by UV–vis absorption and steady state/time resolved fluorescence. The size of NSR dyes is tunable by varying the concentration of rhodamine or surfactant additive. Compared to corresponding molecular rhodamine, the fluorescence lifetime of NSR dyes is 4.5-fold longer, while the emission maximum can be 150 nm larger. Although the increase in size of NSR dyes leads to large red shifts in optical absorption and fluorescence spectra, it does not affect the fluorescence quantum yield and lifetime. On the other hand, the presence of a surfactant (sodium dodecyl benzene sulfonate) not only causes the increase in fluorescence quantum yield, but also greatly extends the fluorescence lifetime of NSR dyes from 1.51 ns to 7.07 ns.

Photoinduced electron transfer (PET) occurring within D4–A was compared to that within D–A, in which A (electron acceptor) was a single zinc phthalocyanine moiety and D (electron donor) a phenothiazine unit, using UV–vis absorption, fluorescence emission and laser flash photolysis. D and A in both models were directly linked by covalent C–N bonds. The symmetrical D4–A system, for which both the synthesis and purification were more straigthforward than for D–A, displayed a much faster PET rate constant; although the D–A system was more difficult to prepare, it exhibited less efficient PET. The charge separation state formed through PET showed long lifetimes on the μs scale in the cases of both the D4–A and D–A molecules.