Light-harvesting antennae based on photoactive silicon nanocrystals functionalized with porphyrin chromophores.

Silicon nanocrystals functionalized with tetraphenylporphyrin Zn(II) chromophores at the periphery perform as light harvesting antennae: excitation of the porphyrin units in the visible spectral region yields sensitized emission of the silicon nanocrystal core in the near infrared with a long lifetime (λ(max) = 905 nm, τ = 130 µs). This result demonstrates that this hybrid material has a potential application as a luminescent probe for bioimaging.

A highly luminescent tetramer from a weakly emitting monomer: acid- and redox-controlled multiple complexation by cucurbit[7]uril.

The tetrahedral, shape-persistent molecule 1(4+), containing four pyridylpyridinium units connected through a central carbon atom, exhibits unexpected photophysical properties including a substantially redshifted absorption (2350 cm(-1)) and a very strong fluorescence (Φem = 40 %), compared with the monomer 2(+) (Φem = 0.4 %). Density functional theory calculations on the structure and spectroscopic properties of 1(4+) and 2(+) show that exciton interactions, homoconjugation, and orbital nature account for the observed differences in their photophysical properties. The protonated tetramer binds four cucurbit[7]uril molecules and the host/guest interactions can be controlled by chemical (acid/base) as well as redox stimuli.

Gold(I)-catalyzed synthesis of γ-vinylbutyrolactones by intramolecular oxaallylic alkylation with alcohols.

Gold(I)-N-heterocyclic carbene (NHC) complexes proved to be a reliable catalytic system for the direct synthesis of functionalized γ-vinylbutyrolactones by intramolecular oxaallylic alkylation with primary alcohols. Good isolated chemical yields were obtained for a range of malonyl and acetate derivatives. The good performance in reagent-grade solvents and the functional group/moisture tolerance make this catalytic process a promising route for the synthesis of architecturally complex polycyclic structures.

Bright long-lived luminescence of silicon nanocrystals sensitized by two-photon absorbing antenna.

Silicon nanocrystals of the average diameter of 5 nm, functionalized with 4,7-di(2-thienyl)-2,1,3-benzothiadiazole chromophores (TBT) and dodecyl chains, exhibit near-infrared emission upon one-photon (1P) excitation at 515 nm and two-photon (2P) excitation at 960 nm. By using TBT chromophores as an antenna we were able to enhance both 1P and 2P absorption cross-sections of the silicon nanocrystals to more efficiently excite their long-lived luminescence. These results chart a path to two-photon-excitable imaging probes with long-lived oxygen-independent luminescence - a rare combination of properties that should allow for a substantial increase in imaging contrast.

Silicon Nanocrystals Functionalized with Pyrene Units: Efficient Light-Harvesting Antennae with Bright Near-Infrared Emission.

Pyrene chromophores were attached to silicon nanocrystals (SiNCs) with diameters of 2.6 and 5.0 nm to provide light-harvesting antennae for enhanced optical absorption. Efficient energy transfer from the pyrene moieties to the SiNCs was observed to induce bright visible (2.6 nm) or near-infrared (NIR) (5.0 nm) photoluminescence (PL). The 5.0 nm diameter pyrene-derivatized SiNCs exhibited NIR PL emission that was insensitive to dioxygen, with a 40% quantum yield and long lifetime (hundreds of µs).