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.
Design, synthesis, characterization, and photodynamic activity of dendritic, water-soluble zinc phthalocyanine (ZnPc) isomers 1a and 1b are described. Bearing terminal triethylene glycol (TEG) moieties as water solubilizing groups that were attached to the Pc core using Cu(I) catalyzed alkyne–azide cycloaddition (CuAAC), 1a and 1b are readily soluble in H2O, polar aprotic, and protic organic solvents. UV/Vis analyses indicate that the Q band of the non-peripheral ZnPc 1b is ca. 80 nm red-shifted relative to the peripheral one with absorption at 805 nm (distilled water). 1a and 1b have log D7.4 values of 0.22 and 0.05, respectively, suggesting that the non-peripheral substitution improved the overall hydrophilicity. Aggregation studies indicate that non-peripherally substituted 1b is significantly less aggregated in aqueous media than peripherally substituted 1a. Singlet oxygen generation studies are reported. Both ZnPcs showed negligible dark toxicity on bacteria and yeast with 10 μM 1a and 1b. Illumination (400–850 nm) of Pseudomonas aeruginosa with 10 μM of 1a produced a 90% cell inactivation while Acinetobacter baumannii with 10 μM 1b showed detection limit (99.9999+%) cell inactivation, demonstrating the antimicrobial photoactivity of these dyes.
PMID: 15675869;Abstract:
(Chemical Equation Presented) A series of 3,5-poly(aryl ether) dendrons was prepared up to the third generation using inexpensive 3,5-di-tert-butyl-4- hydroxytoluene (BHT, 1) as a starting material.
Abstract:
The synthesis and solution and thin-film characterization of eight octasubstituted dendritic phthalocyanines (Pcs) and their zinc complexes are reported. The Pc chromophore was substituted in the 2,3,9,10,16,17,23,24- positions with three generations of benzylaryl ether dendrons with either a benzyl (3a-3c) or 3,5-di-t-butylbenzyl periphery (3d-3f). Visible spectra in solution (CH2Cl2-EtOH mixtures, toluene, THF, dioxane, acetone, and EtOAc) indicated a varying degree of chromophore aggregation that depended on solvent, dendrimer generation, and whether the Pc was metallated. Variable-concentration visible spectroscopic studies were analyzed using a nonlinear least-squares fitting procedure giving Kd values. These values further quantitated the observations that the t-butyl-substituted dendrimers 3d-3f were all less prone to aggregation in solution than the unsubstituted dendrimers 3a-3c, with a monotonic decrease in Kd across the series 3a → 3b → 3c → 3d → 3e → 3f. Second-generation t-butyl-substituted dendrimer 3f showed little to no aggregation in all solvents studied. Thin-film studies indicated that the largest members of the two dendrimer groups, third-generation 3c and second-generation 3f, were largely monomeric as evidenced by split Q-bands, similar to that seen in dilute CH2Cl2 solution when deposited via spin-coating onto glass slides. The metallated zinc Pcs 4a-4f all exhibited significantly less tendency toward aggregation in both solution and thin-films than their unmetallated analogues.
Abstract:
We have investigated the microstructure of the low molecular weight oligomers using a number of spectroscopic techniques and have identified them as resulting from a true chain transfer mechanism. This is strong evidence for the existence of a ruthenium alkylidene active complex formed from cross-metathesis with an acyclic olefin, which is capable of further productive metathesis.
