Dominic V Mcgrath
Publications
Abstract:
Several new azobenzene-containing dendritic molecules have been prepared and characterized. The photoresponsive characterization of these dendrimers illustrates the insensitivity of the photochromic behavior of the azobenzene with respect to the nature of the attached dendritic fragment.
Using a monolayer of zinc phthalocyanine (ZnPcPA) tethered to indium tin oxide (ITO) as a model for the donor/transparent conducting oxide (TCO) interface in organic photovoltaics (OPVs), we demonstrate the relationship between molecular orientation and charge-transfer rates using spectroscopic, electrochemical, and spectroelectrochemical methods. Both monomeric and aggregated forms of the phthalocyanine (Pc) are observed in ZnPcPA monolayers. Potential-modulated attenuated total reflectance (PM-ATR) measurements show that the monomeric subpopulation undergoes oxidation/reduction with ks,app = 2 × 102 s–1, independent of Pc orientation. For the aggregated ZnPcPA, faster orientation-dependent charge-transfer rates are observed. For in-plane-oriented Pc aggregates, ks,app = 2 × 103 s–1, whereas for upright Pc aggregates, ks,app = 7 × 102 s–1. The rates for the aggregates are comparable to those required for redox-active interlayer films at the hole-collection contact in organic solar cells.
Abstract:
Amphiphilic dendritic structures having a photoresponsive azobenzene moiety linked between a hydrophilic crown ether receptor and a hydrophobic dendritic sector were prepared and characterized. These dendritic structures exhibit typical azobenzene moiety on the phase behavior is investigated.
Asymmetric zinc phthalocyanine (ZnPc) isomers with triethylene glycol (TEG) moieties in the peripheral (1a) and non-peripheral (1b) substitution were designed, synthesized, characterized, and their phototoxicity on colon-26 cells evaluated. TEG moieties as water solubilizing groups were incorporated at peripheral or non-peripheral positions to investigate the effect of their position on the Pc on the photodynamic activity. UV/vis analyses indicated a small red-shifting of the Q band of the non-peripheral ZnPc–TEG 1b (ca. 4 nm) relative to 1a in dichloromethane and THF. n-Octanol/pH 7.4 buffer partition coefficients revealed that 1b was marginally more hydrophilic than 1a with log D7.4 values of 2.44 and 2.46, respectively. Fluorescence emission aggregation studies indicate that 1b is ca. 61% (DMSO) and 32% (phosphate buffer) less aggregated than the peripherally substituted ZnPc 1a suggesting that non-peripheral substitution decreased overall aggregation of the photosensitizers. Singlet oxygen generation studies are reported. Both ZnPc–TEGs showed negligible dark toxicity on colon 26 cells with 10 μM 1a and 1b. Irradiation (690 nm, 45 J/cm2) of the cells produced an IC50 value >25 μM for 1a and an IC50 value between 1 and 5 μM for 1b. Overall, the non-peripheral isomer 1b was found to be more photodynamically active.
Abstract:
In the past two and a half decades, dendrimers have emerged as a distinct branch of macromolecular chemistry. Tailoring of dendrimer structure yields precise placement of chromophores that can serve as energy harvesters, mimicking photosynthesis. The unique architecture afforded by dendrimers allows for multiple energy harvesters that can transfer their energy to a single core, which is important for optoelectronic applications such as organic light emitting diodes (OLEDs). This review emphasizes the energy transfer characteristics that these dendrimers provide rather then their synthesis. © 2008 Springer-Verlag.