Photophysical properties are reported for a series of cyclometalated platinum and iridium complexes that can serve as photosensitizers for singlet oxygen. The complexes have the formula (C;N)(2)Ir(O;O) or (C;N)Pt(O;O) where C;N is a monoanionic cyclometalating ligand such as 2-(phenyl)pyridyl and 2-(phenyl)quinolyl, and O;O is the ancillary ligand acetylacetonate (acac) or dipivaloylmethane (dpm). Also examined were a series of (N;N)PtMe(2) complexes where N;N is a diimine such as 2,2'-bipyridyl. In general, the cyclometalated complexes are excellent photosensitizers for the production of singlet oxygen, while the (N;N)PtMe(2) complexes were ineffective at this reaction. Quantum yields of singlet oxygen production range from 0.9-1.0 for the cyclometalated Pt complexes and 0.5-0.9 for Ir complexes. Luminescence quenching and singlet oxygen formation of the Ir complexes occurs from a combination of electron and energy transfer processes, whereas the Pt complexes only react by energy transfer. For Ir complexes with low emission energy, physical deactivation of the triplet excited state becomes competitive with energy transfer to ground state dioxygen. The rates of singlet oxygen quenching for the complexes presented here are in the range 6 x 10(6)-2 x 10(7) M(-1) s(-1) for Pt complexes and 2 x 10(5)-2 x 10(7) M(-1) s(-1) for Ir complexes, respectively. Differences in the efficiency of both forming and quenching singlet oxygen between the Ir and Pt cyclometalates are believed to come about from the more exposed coordination geometry in the latter species.

We report the singlet oxygen sensitization properties of a series of bis-cyclometalated Ir(III) complexes (i.e., (bt)2Ir(acac), (bsn)2Ir(acac), and (pq)2Ir(acac); bt = 2-phenylbenzothiazole, bsn = 2-(1-naphthyl)benzothiazole, pq = 2-phenylquinoline, and acac = acetylacetonate). Complexes with acetylacetonate ancillary ligands give singlet oxygen quantum yields near unity (PhiDelta = (0.7-1.0) +/- 0.1), whether exciting the ligand-based state or the lowest energy excited state (MLCT + 3LC). The singlet oxygen quenching rates for these beta-diketonate complexes were found to be small [(5 +/- 2) x 105 to (6 +/- 0.2) x 106 M-1 s-1], roughly 3 orders of magnitude slower than the corresponding phosphorescence quenching rate. Similar complexes were prepared with glycine or pyridine tethered to the Ir(III) center (i.e., (bsn)2Ir(gly) and (bt)2Ir(py)Cl; gly = glycine and py = pyridine). The glycine and pyridine derivatives give high singlet oxygen yields (PhiDelta = (0.7-1.0) +/- 0.1).

Water-soluble quantum dot -organic dye nanocomposites have been prepared via electrostatic interaction. We used CdTe quantum dots with diameters up to 3.4 nm, 2-aminoethanthiol as a stabilizer, and meso-tetra (4-sulfonatophenyl) porphine dihydrochloride (TSPP) as an organic dye. The photophysical properties of the nanocomposite have been investigated. The fluorescence of the parent CdTe quantum dot is largely suppressed. Instead, indirect excitation of the TSPP moiety leads to production of singlet oxygen with a quantum yield of 0.43. The nanocomposite is sufficiently photostable for biological applications.Colloidal semiconductor nanocrystals (Quantum Dots, QDs) can provide three-dimensional (3D) architectures and have attracted widespread interest, since their nano-size physical properties are quite different from those of bulk materials. 1 QDs photoluminescence can be size-tuned to improve spectral overlap with a particular acceptor, and having several acceptors interact with a single QDs donor substantially improves fluorescence resonance energy transfer (FRET) efficiency. Retaining the small probe size is critical for successful in vivo applications since large-sized probes significantly reduce biostability, diffusion, and circulation processes, and increase undesired nonspecific binding. 2 The small size of QDs is valuable for enhancing biological targeting efficiency and specificity. 3 Photodynamic therapy (PDT) is an emerging modality for the treatment of a variety of oncological, dermatological, and other types of cancer. 4 Singlet oxygen ( 1 O 2 ) is believed to be a major cyctotoxic species in this process. There have been several reports of nanoparticles as carriers for singlet oxygen photosensitizers. 5-7 Nanoparticles can be ideal carriers of photosensitizer molecules for PDT. Moreover, some nanomaterials can generate singlet oxygen. 8,9 Although this area has not received as much attention as the application of nanomaterials to electronics or catalysis, it represents a promising route to overcoming many We report herein the preparation of water-soluble QDs, using Meso-Tetra (4-sulfonatophenyl) Porphine Dihydrochloride (TSPP) as a photosensitizer, bound to CdTe nanocrystals via electrostatic interactions. The advantage of the electrostatic approach used in our work is that it allows control over the assembly behavior in solution. 14 The CdTe QDs were synthesized with 2-aminoethanethiol as surface stabilizer. Synthesis of yellow photofluorescence CdTe nanocrystal was performed via a modified protocol adopted from the literature. 15 The CdTe QDs revealed size-dependent luminescence with maxima at 560 nm. In a typical assay, the UV-vis spectra of QD-TSPP nanocomposites shifted slightly to the blue region,compared with free TSPP (Figure 1a). This could be surface caused by surface plasma changes as TSPP deposited on the of the QDs aggregates. 16 The UV-vis peak of CdTe-TSPP nanocomposites increased with the concentration of added TSPP.Immediate aggregation was observed when the concentration of...

Several water-soluble cobalt(III) complexes were employed as precursors to form cobalt oxide nanostructures. These complexes were incorporated into polyelectrolyte multilayers precoated onto colloidal particles, followed by calcination. Cobalt complexes with strong intermolecular hydrogen bonding form one-dimensional Co 3 O 4 nanotube structures. Short Co 3 O 4 nanotubes with defects and broken spheres are formed when cobalt complexes with weak or no intermolecular hydrogen bonding are used. The sites for disulfide bond formation present on some complexes were found to be unessential for the nanotube formation.