Noncoherent low-power photon upconversion has been realized in solid thin films composed of an ethyleneoxide/epichlorohydrin copolymer doped with palladium octaethylporphyrin (PdOEP) and 9,10-diphenylanthracene (DPA). Selective excitation of PdOEP at 544 nm generates easily visualized DPA fluorescence in the blue with noncoherent light sources under ambient laboratory conditions. The incident excitation power dependence is quadratic in nature, exemplifying that sequential one-photon absorption by PdOEP leads to the sensitization of two triplet DPA chromophores, which in turn annihilate to produce the upconverted singlet DPA fluorescence. Time-resolved emission experiments confirm that the solid host facilitates these sequential bimolecular reactions leading to delayed DPA fluorescence; however, these processes are notably slower than the analogous photochemistry in fluid solution.

A "cluster-bomb"-like lipid-dendrimer nanoassembly synergizes the functions of its components and thereby efficiently accomplishes the drug delivery cascade for high efficacy in treating cancer. The nanoassembly successfully circulates in the blood and accumulates in the tumor. Once in the tumor, it releases small dendrimers that act like "bomblets", enabling tumor penetration, cell internalization, and drug release.

Rheology and turbidity measurements were performed under similar thermal histories to probe the relationship between thermoreversible gelation and phase separation for a set of three methylcellulose (MC) materials with similar degrees of substitution (DS) and contrasting molecular weights after hydration in cold water. Frequency-independent loss tangents were used to identify the gel point (T gel ) in MC solutions well over the chain overlap concentration (c ≥ 10c*). Transmittance of 633 nm laser light through the solutions revealed that all MC solutions cloud upon gelling, with a relative transmittance of 86% closely associated with the gel point. The gelation temperature of MC solutions was found to decrease with increasing MC concentration and the results for all molecular weights superposed. Using gel and cloud points, a phase diagram was constructed which reveals that clear MC solutions transition directly into turbid gels. Frequency-independent storage moduli of fully developed MC gels scaled with φ 2.3 , consistent with theory and experiment of entangled systems. Gelation of MC has strong dependence on heating rate while the melting of the gel has little dependence on cooling rate, suggesting that thermogelation of MC proceeded by a nucleation and growth mechanism rather than spinodal decomposition.

Abstract:The upconverting properties of a dye cocktail composed of palladium(II) octaethylporphyrin (PdOEP, triplet sensitizer) and 9,10-diphenylanthracene (DPA, triplet acceptor/annihilator) were investigated as a function of temperature in several low glass transition temperature (T g ) polymer hosts including an ethyleneoxide-epichlorohydrin copolymer (EO-EPI) and the polyurethanes Texin 270, Texin 285, and Tecoflex EG-80A. Selective excitation of PdOEP at 544 nm in the presence of DPA in these materials resulted in anti-Stokes blue emission from DPA, a consequence of sensitized triplet-triplet annihilation (TTA) photochemistry, confirmed by the quadratic dependence of the upconverted fluorescence intensity with respect to incident light power. The upconversion process was completely suppressed by cooling a PdOEP/DPA blend film to below the T g of the respective polymer. However, the blue emission was clearly visible by the naked eye upon heating these films to room temperature (290 K). Subsequently, the upconverted emission intensity increased with increasing temperature and was found to be completely reversible upon several heating and cooling cycles provided the temperature remained below 400 K. Heating samples above this temperature resulted in unrecoverable failure of the material to produce upconverted photons. The phosphorescence intensity decay of PdOEP in the polymer host, Tecoflex EG-80A, adequately fits to a sum of two exponential functions as well as the Kohlrausch-Williams-Watts (KWW) stretched exponential model. Increasing the temperature of the film increases the complexity and heterogeneity of the system as evidenced by the lower values obtained from the KWW model as the temperature increases.