Jing-Rong Chen

Photooxidative degradation mechanism of model compounds of poly(p-phenylenevinylenes) (PPVs)

Abstract Seven model compounds of poly( p -phenylenevinylenes) [M-PPVs] were designed to perform the photooxidative degradation experiments. The degradation rates of M-PPVs depend on the nature, number, and position of substituents. The transient species including singlet oxygen, superoxide radical anion, M-PPV triplet state, M-PPV radical cation and anion in M-PPV photodegradation were observed and characterized systematically with ESR spin trapping, pulse radiolysis, and laser flash photolysis techniques. By using rose bengal, methylene blue, fullerene, tetraphenyl porphyrin, 9,10-dicyanoanthracene, or biacetyl as sensitizer in dye-sensitized M-PPV photodegradation experiments, we found that singlet oxygen does not play the principal role as previous reported. Results of triplet–triplet energy transfer from biacetyl to M-PPVs and M-PPV triplet state quenching by 1,4-diazabicyclo[2.2.2] octane (DABCO) suggested that the reaction between M-PPV triplet state and oxygen is really the key step in the processes of photodegradation of the conjugated structure.

Synthesis of a water-soluble cyclodextrin modified hypocrellin and ESR study of its photodynamic therapy properties

A water-soluble cyclodextrin modified hypocrellin B (HBCD) was designed and synthesized. HBCD retained the phototherapeutic properties and exhibited much stronger photoinduced damage to calf thymus DNA (CT DNA) than hypocrellin B and mercaptoacetic acid substituted hypocrellin B (MAHB). The mechanism of electron transfer from CT DNA to the triplet state of HBCD was confirmed by steady-state electron spin resonance (ESR) and a time-resolved ESR study.

A new Co(III)–hypocrellin B complex with enhanced photonuclease activity

Hypocrellin B (HB), a naturally occurring photosensitizer, has been extensively and intensively studied as a promising photodynamic therapy (PDT) agent. In this work, a new Co(III) complex [Co(2)(HB)(tmp)(4)](4+) (tmp=3,4,7,8-tetramethyl-1,10-phenanthroline) was designed and synthesized with HB as bridging ligand and tmp as terminal ligand. [Co(2)HB(tmp)(4)](4+) exhibits improved water solubility, enhanced absorptivity in the phototherapeutic window, increased binding affinity and DNA photocleavage capability toward dsDNA with respect to HB. The photodynamic activity of [Co(2)(HB)(tmp)(4)](4+) stems from its (1)O(2) photosensitization ability, in sharp contrast to [Cu(2)(HB)(tmp)(2)](2+) which relies on superoxide anion radical (O(2)(-)) and hydroxyl radical (·OH) to photocleave DNA, though the both complexes possess similar electrochemical properties. The remarkable difference between the photodynamic mechanisms of [Co(2)(HB)(tmp)(4)](4+) and [Cu(2)(HB)(tmp)(2)](2+) was discussed in detail.

Using electrostatic interactions to increase the photodamaging ability of hypocrellin B: synthesis and study of 2-(dimethylamino)ethanethiol-modified HB

A new 2-(dimethylamino)ethanethiol-modified HB derivative was synthesized and enhanced photodamaging ability towards DNA was achieved by making use of the electrostatic attraction.

Photodynamic properties of supramolecular assembly constructed by magnesium complex of hypocrellin A and fullerene C60

A supramolecular assembly, composed of magnesium complex of hypocrellin A (Mg2+–HA) and pristine C60 with a molar ratio of 2 : 1, is constructed and characterized. The supramolecular assembly (Mg2+–HA/C60) shows moderate solubility in polar solvents and strong absorption in visible region. EPR studies demonstrate that one-electron transfer from N,N-diethylaniline (DEA) to excited-state Mg2+–HA induces the generation of the reduced form of Mg2+–HA (Mg2+–HA−˙ radical), followed by electron transfer from the Mg2+–HA−˙ radical to C60, forming the corresponding anion radical C60−˙ under anaerobic conditions. In aerobic media, the generation of reactive oxygen species, including superoxide anion radical (O2−˙) and singlet oxygen (1O2), by Mg2+–HA/C60 photosensitization is observed. Mg2+–HA/C60 exhibits much stronger photodamage ability on pBR322 plasma DNA than Mg2+–HA and HA under both aerobic and anaerobic conditions.

The photodynamic property improvement of hypocrellin A by chelation with lanthanum ions

A 1:1 complex of lanthanum ion with hypocrellin A (La3+-HA) possessing high singlet oxygen generation efficiency, large absorbance in the phototherapeutic window, and great water solubility exhibits promising photodynamic properties.

Photoinduced intramolecular electron transfer and exciplex formation in anthracene and pyrene binary compounds

Abstract Two series of six donor–acceptor binary compounds, pyrene–dicyanovinylbenzene (Py- n -DCVB) and anthracene–dicyanovinylbenzene (An- n -DCVB), with different chain lengths were designed and synthesized. Using steady state spectroscopy and time resolved spectroscopy, the effects of solvent polarity, viscosity, temperature and salt content were studied. The photoinduced electron transfer and exciplex formation processes, as a function of the dynamics of chain conformation and the size of electron donor unit, are discussed and compared respectively for all six binary compounds.

Amphiphilic porphyrins in reverse micelles: the influence of the molar ratio of water to surfactant and side-chain length on their triplet-state lifetimes. A case study

Using bis(2-ethylhexyl) sodium sulfosuccinate (AOT) as surfactant, a series of amphiphilic porphyrins terminated with imidazole were studied in AOT/isooctane/water reverse micelles, intending to mimic the relationship between microenvironments in organisms and the amphiphilic properties of porphyrins for photodynamic therapy (PDT) applications. Laser flash photolysis experiments and fluorescence quenching of porphyrins by phenothiazine show that longer side-chain lengths and higher molar ratio of water to AOT (wo) of reverse micelles promotes firm embedding of porphyrin molecules in the interfacial region of reverse micelles. Such an embedding may shift porphyrins from aggregated to monomeric form in reverse micelles and, accordingly, the slower excited-state decay may increase the efficiency of the photosensitizer in PDT. The variation in the ability of singlet oxygen generation detected by ESR also supports such a conclusion. The effect of amphiphilic properties on the status of porphyrins in microenvironments provides light on the synthesis of other amphiphilic porphyrins for PDT applications.

Porphyrin capped TiO2 nanoclusters, tyrosine methyl ester enhanced electron transfer

The photoinduced electron transfer between neutral titanium dioxide nanoclusters and porphyrin is enhanced by the bridging of tyrosine methyl ester to the two components.

Study on emission quenching by 2,2,6,6-tetramethyl-1-piperidinyloxy free radical

The emission quenching mechanism of four emissive compounds by 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) was investigated using steady state and transient state spectroscopy. The quenching mechanism was considered to be the radical triplet pair mechanism (RTPM) from the experimental results of both the emission quenching study and the steady state and time resolved electron spin resonance (SSESR and TRESR) studies.