Dendrimers as photochemical reaction media. Photochemical behavior of unimolecular and bimolecular reactions in water-soluble dendrimers (original) (raw)
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Journal of the American Chemical Society, 2004
Water-soluble poly(alkyl aryl ether) dendrimers have been explored for their use as hosts of organic substrates in aqueous media. Prototypical photoreactions, namely, photo-Fries reaction of (a) 1-naphthyl benzoate and (b) 1-naphthyl phenyl ester and R-cleavage reaction of (a) dibenzyl ketones and (b) benzoin alkyl ethers, have been examined. We find that a dendritic microenvironment not only restricts the mobility of radical intermediates but also rigidly encapsulates the substrate, intermediates, and products from "leaking" to the bulk environment. Comparative studies of the same photoreactions in micellar media demonstrate that dendritic media offer much better constrainment than the micelles.
Photoactivity and pH Sensitivity of Methyl Orange Functionalized Poly(Propyleneamine) Dendrimers
Macromolecules, 2002
For the first time a pH indicator that responds to two different external stimuli, i.e. pH and light, namely methyl orange, has been implemented in a dendrimer. Six generations (G0-G5) of methyl orange-functionalized poly(propyleneamine) dendrimers ("MO dendrimers") have been synthesized and characterized using 1 H NMR, 13 C NMR, and MALDI-TOF mass spectrometry. Subsequently, the response of the MO dendrimers toward pH changes has been monitored using UV-vis spectroscopy and the photophysical properties have been investigated. Furthermore, the photoisomerization from E to Z and the thermal recovery from Z to E, have been studied using UV-vis and transient-absorption spectroscopy. Interestingly, the response of the MO units toward pH changes is found to be generation dependent. On the other hand, the photophysical properties are found to be similar for all generations, except for the value, which deviates significantly from the expected value in the case of G4 and G5. Also the isomerization processes show no generation dependence within the same solvent, but different rate constants for the Z/E isomerization have been observed for different solvents.
Photophysical properties of Newkome-type dendrimers in aqueous medium
Photochemical & Photobiological Sciences, 2007
Newkome-type first, second and third generation dendrimers, having t-butyl (GB), ethyl (GE) and carboxylic (GA) end groups, were synthesized. A pyrene group, which can act as fluorescent sensor, was attached to the core of the dendrimers and their photophysical properties in aqueous solution were studied. These dendrimers were found to aggregate in aqueous solution, which manifested as an excimer peak in the pyrene emission spectra for the first and second generation dendrimers with ethyl and t-butyl end groups. The excimer peak however was not seen in case of the third generation dendrimer. Dendrimers with carboxylic end groups, did not show the excimer peak in water, which implies the hydrophobic nature of the aggregation. It is observed that the intensity of the excimer peak decreases with the increase in the size of the dendrimer. Lifetime studies carried out on the first and second generation dendrimers showed the formation of excimer species as a risetime in the decay curve. The aggregation of the third generation dendrimer was proposed from the quenching studies using silver ions and CCl 4 as quenchers.
Dendrimers Chemistry and Applications: A Short Review
2020
Dendrimers, also known as cascade molecules, arborols, cauliflower or starburst polymers. They are monodisperse, symmetrical, macromolecules with tree like 3D-architecture consists of end-groups, central core and branching units associated to periphery and possess extremely constraint size, topography and surface characteristics like density, backfolding, intrinsic viscosity, light harvesting property, photophysical properties that are fairly distinct from linear polymers. Different types of dendrimers, on the basis of their different properties and associated functional groups, has been studied yet in which one of the unique group of dendrimers is dendrtic co-polymer possess two types, first are layer block dendrimers and second are segment block dendrimers. Some new types of dendrimers like IrC3, IrCl and IrF2 have been also synthesized by divergent or convergent methods of synthesis. Dendrimers have a lot of applications in different fields like nanotechnology, medical chemistry,...
Photoactive and Electroactive Dendrimers: Future Trends and Applications
Australian Journal of Chemistry, 2011
The initial interest in dendrimer chemistry was the synthesis of such aesthetically pleasant macromolecules. Nowadays, the field is moving to applications in various multidisciplinary areas, such as medicine, biology, chemistry, physics, and engineering, i.e. at the interface of many disciplines. This short review describes some promising applications of photoactive and electroactive dendrimers as artificial enzymes, molecular batteries, sensors with signal amplification, photoswitchable hosts, systems for energy up-conversion, and light-harvesting antennas. The reported examples clearly show that these applications take advantage of the unique aspects of dendrimer structure: (i) three-dimensional array; (ii) generation-dependent size; (iii) presence of selected functional units in predetermined sites; and (iv) endo-and exo-receptor capabilities.
European Polymer Journal, 2004
Some novel fluorescent poly(amidoamine) dendrimers supported by a polyamide-6 matrix have been prepared and studied for the first time. The colour characteristics of the novel materials have been determined and found to be dependent on the nature of 1,8-naphthalimides bonded to their periphery amino groups. The materials have been treated with protons and cuprum cations. The resulting into changes in the colour characteristics and photostability of the dendrimers has been investigated. It has been shown that these ions inhibit the photodegradation of dendrimers molecules studied.
Journal of Polymer Science Part A: Polymer Chemistry, 2004
Three sets of aliphatic polyester dendrimers based on 2,2-bis(methylol)propionic acid (bis-MPA) were synthesized. Two of the sets had benzylidene terminal groups and either a trimethylolpropane or triphenolic core moiety. The last set had acetonide terminal groups and a triphenolic core moiety. Benzylidene-[G#1]-anhydride and acetonide-[G#1]-anhydride were used as the reactive building blocks in the construction of all dendrimers. The large excess of building blocks used in the coupling reactions initially resulted in considerable material loss. This waste was eliminated through the development of a recycling method. 1 H and 13 C NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis were used to verify the purity of all compounds. Size exclusion chromatography (SEC) was used, as well as MALDI-TOF, for molecular weight determinations. The SEC measurements were conducted with a universal calibration method and an online right-angle laser light scattering detector. Measured dendrimer molecular weights were close to their theoretical molar masses. Observations were also made of the hydrodynamic radius and intrinsic viscosity for the different dendrimers.