Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra

The development of a time-resolved coherent anti-Stokes Raman scattering (CARS) variant for use as a probe of excited electronic state Raman-active modes following excitation with an ultrafast pump pulse is detailed. Application of this technique involves a combination of broadband fs-time scale pulses and a narrowband pulse of ps duration that allows multiplexed detection of the CARS signal, permitting direct observation of molecular Raman frequencies and intensities with time resolution dictated by the broadband pulses. Thus, this nonlinear optical probe, designated fs/ps CARS, is suitable for observation of Raman spectral evolution following excitation with a pump pulse. Because of the spatial separation of the CARS output signal relative to the three input beams inherent in a folded BOXCARS arrangement, this technique is particularly amenable to probing low-frequency vibrational modes, which play a significant role in accepting vibrational energy during intramolecular vibrational energy redistribution within electronically excited states. Additionally, this spatial separation allows discrimination against strong fluorescence signal, as demonstrated in the case of rhodamine 6G.     

Synthesis and DNA interactions of a bis-phenothiazinium photosensitizer

We report the synthesis and characterization of N,N-bis[(7-dimethylamino)phenothiazin-5-ium-3-yl]-4,4-ethylenedipiperidine diiodide (3), consisting of two photosensitizing phenothiazinium rings attached to a central ethylenedipiperidine linker. At all time points (10, 30, 60 min) and all wavelengths (676, 700, 710 nm) tested, photocleavage of pUC19 plasmid DNA (22 degrees C and pH 7.0) was markedly enhanced by 1 microM of 3 in comparison to 1 microM of the parent phenothiazine methylene blue (MB). At concentrations of phenothiazine ranging from 5 to 0.5 microM, the photocleavage levels produced by compound 3 were consistently higher than the cleavage produced using approximately twice the amount of MB (e.g., 710 nm irradiation of 5 microM of 3 and 10 microM of MB cleaved the plasmid DNA in 93% and 71% yields, respectively). Scavenger assays provided evidence for the involvement of singlet oxygen and, to a lesser extent, hydroxyl radicals in DNA damage. Analysis of photocleavage products at nucleotide resolution revealed that direct strand breaks and alkaline-labile lesions occurred predominantly at guanine bases. While compound 3 and MB were both shown to stabilize duplex DNA, the DeltaTm values of calf thymus (CT) and C. perfringens DNAs were approximately three fold higher in the presence of compound 3. Finally, viscometric data indicated that CT DNA interacts with compound 3 and MB by a combination of groove binding and monofunctional intercalation, and with compound 3 by a third, bisintercalative binding mode.     

LIPOSOMAL DELIVERY OF A PHOTOSENSITIZER, BENZOPORPHYRIN DERIVATIVE MONOACID RING A (BPD), TO TUMOR TISSUE IN A MOUSE TUMOR MODEL

Abstract— Biodistribution studies were carried out on ¹⁴C-labeled benzoporphyrin derivative monoacid ring A (BPD), which had been formulated as a unilamellar liposome or taken from a stock solution in dimethyl sulfoxide diluted into phosphate-buffered saline immediately before intravenous injection into DBA/2 mice. By and large the general distribution of BPD to various organs and tissues was comparable for both formulations. It was noted, however, that liposomal material appeared to enter tissues more rapidly and to be cleared more rapidly, as demonstrated by shorter half-lives for a number of tissues including skin, lung and fat, and generally lower levels in most tissues 24 h following administration. Accumulation in tumor tissue was slightly higher with liposomal BPD, and clearance rates for this tissue were equivalent (half-lives 16.1 h for liposomal BPD and 16.9 h for aqueous BPD). When the two preparations were tested in a bioassay in tumor-bearing mice, photodynamic therapy (PDT) with liposomal BPD proved to be superior to the aqueous preparation when PDT was administered 3 h following intravenous administration of BPD. Plasma distribution studies in vitro demonstrated that 91.1 ± 0.3% of the liposomal BPD distributed to the lipoprotein fraction within the first hour of mixing, whereas only 49.1 ± 2.6% of nonliposomal BPD was associated with lipoprotein under the same conditions. Furthermore, while lipoprotein-associated liposomal BPD distributed evenly between all three types of lipoprotein (high, low and very low density), a majority of nonliposomal BPD associated with the high-density lipoprotein fraction.     

Enhancing Fullerene‐Based Solar Cell Lifetimes by Addition of a Fullerene Dumbbell

Cost‐effective, solution‐processable organic photovoltaics (OPV) present an interesting alternative to inorganic silicon‐based solar cells. However, one of the major remaining challenges of OPV devices is their lack of long‐term operational stability, especially at elevated temperatures. The synthesis of a fullerene dumbbell and its use as an additive in the active layer of a PCDTBT:PCBM‐based OPV device is reported. The addition of only 20 % of this novel fullerene not only leads to improved device efficiencies, but more importantly also to a dramatic increase in morphological stability under simulated operating conditions. Dynamic secondary ion mass spectrometry (DSIMS) and TEM are used, amongst other techniques, to elucidate the origins of the improved morphological stability.     

Highly Deformed o-Carborane Functionalised Non-linear Polycyclic Aromatics with Exceptionally Long C−C Bonds

The effect of substituting o-carborane into the most sterically hindered positions of phenanthrene and benzo(k)tetraphene is reported. Synthesised via a Bull–Hutchings–Quayle benzannulation, the crystal structures of these non-linear acenes exhibited the highest aromatic deformation parameters observed for any reported carborane compound to date, and among the largest carboranyl C−C bond length of all organo-substituted o-carboranes. Photoluminescence studies of these compounds demonstrated efficient intramolecular charge-transfer, leading to aggregation induced emission properties. Additionally, an unusual low-energy excimer was observed for the phenanthryl compound. These are two new members of the family of carborane-functionalised non-linear acenes, notable for their peculiar structures and multi-luminescent properties.