Photophysical properties of Newkome-type dendrimers in aqueous medium (original) (raw)
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Macromolecules, 2004
Protected Newkome-type second-generation dendrimers (based on Lin's amine) were synthesized with a pyrene moiety attached to the core. The photophysical property in aqueous solution of the protected dendrimers shows self-association behavior in water. Pyrene excimer emission at 475 nm is observed in water even at very low concentrations of protected dendrimer (ca. 5 × 10-8 M). This emission band is absent in other solvents even up to a concentration of 10-5 M. The corresponding unprotected dendrimer does not show the pyrene excimer fluorescence. The amide of pyrene butyric acid with tert-butylamine shows the formation of excimer, albeit with very low intensity. Quenching studies on the dendrimer with hydrophilic quencher iodide anion (I-) reveal that there is significant quenching of fluorescence intensity in the case of N-tert-butyl-4-pyren-1-ylbutyramide as compared to that of the pyrene-attached second-generation protected dendrimer. This shows that the pyrene moiety in the case of the protected dendrimer is significantly shielded from the surrounding.
The Journal of …, 2005
Synthesis and studies of poly(alkyl aryl ether) dendrimers, possessing carboxylic acid functionalities at their peripheries, are reported. 5-Bromopentyloxy methylisophthalate was utilized as the monomer to O-alkylate the phenolic hydroxyl groups of poly(alkyl aryl ether) dendrimers. Dendrimers of first, second, and third generations, possessing 6, 12, and 24 carboxylic acids, respectively, were thus prepared. These dendrimers were soluble in alkaline aqueous solutions, and the ensuing microenvironmental properties of the aqueous solutions were assessed by pyrene solubilization studies. Upon establishing the presence of nonpolar microenvironments within the dendritic structures, solubilizations of few organic substrates were conducted and their photochemical behaviors were assessed. Specifically, the photolysis of 1-phenyl-3-p-tolyl-propan-2-one and benzoin ethyl ether and photodimerization of acenaphthylene were conducted. These studies revealed that the product distribution and the "cage effect" were more distinct and efficient for the third generation dendrimer, than for the first and second generation dendrimers. The photochemical studies of carboxylic acid functionalized dendrimers were compared to that of hydroxyl group terminated poly(alkyl aryl ether) dendrimers.
Journal of Polymer Science Part A: Polymer Chemistry, 2007
New light emitting dendrimers were synthesized by reacting 3,5-bis-(3,5bis-benzyloxy-benzyloxy)-benzoic acid or 3,5-bis-[3,5-bis-(3,5-bis-benzyloxy-benzyloxy)benzyloxy]-benzoic acid with a carbazolyl vinyl spirobifluorene moiety. A blue-emitting core dye was encapsulated by multibenzyloxy dendrons, and two dendrimers having different densities of dendrons were prepared. Photoluminescence (PL) studies of the dendrimers demonstrated that at the higher density of benzyloxy dendrons, the featureless vibronic transitions were improved, causing lesser excimer emission. The similarity of the solution and solid emission spectra of the larger dendrimer, 10, revealed the suppression of molecular aggregation in the solid film, which is attributed to the presence of the bulky benzyloxy dendrons. The electroluminescence spectra of multilayered devices made using 10 predominantly exhibited blue emissions; similar emission was observed in the PL spectra of its thin film. The multilayered devices made using 3, 9, and 10 showed luminances of 1021 cd m À2 at 5 V, 916 cd m À2 at 6 V, and 851 cd m À2 at 6.5 V, respectively. The largest dendrimer, 10, bearing a greater number of benzyloxy dendrons, exhibited a blue-like emission with CIE 1931 chromaticity coordinates of x ¼ 0.16 and y ¼ 0.13, which is due to the influence of a higher shielding effect. V
Analytica Chimica Acta, 1999
Alternant and nonalternant polycyclic aromatic hydrocarbons (PAHs) are employed to compare carboxylate-terminated polyamido amine (PAMAM) dendrimers to typical anionic micelles. Nitromethane is a known, selective, quenching agent of alternant PAHs. However, recent studies by Acree and co-workers have found that nitromethane will also quench the fluorescence emission intensity of nonalternant PAHs in the presence of anionic surfactants above the critical micelle concentration. The quenching of alternant and nonalternant PAHs by nitromethane is used to compare dendritic 'unimolecular micelles' to traditional micelles. Experimental results indicate that the PAHs' association with these dendrimers does not appear to occur in the 'palisade' region, as seen in traditional micelles, but rather deeper within the dendrimer structure. Solvent polarity probe studies and quenching in the absence of nitromethane also support this conclusion. Due to the fact that the PAHs do not reside near the negatively charged surface groups, the nitromethane selective quenching rule is obeyed in carboxylate-terminated PAMAM dendrimers (10 mM in surface groups).
Journal of Polymer Science Part A: Polymer Chemistry, 2007
An inexpensive and highly efficient synthesis of first example of fluorescent aromatic dendrimers having alternative ether and urea linkages without the need for protection and deprotection steps has been developed. Dendrons and dendrimers up to third generation, with amine end-groups, were prepared by convergent growth approach in high yield. A repetitive synthetic sequence of nucleophilic addition reaction between amine and regenerated isocyanate and reduction of nitro groups into amine are adopted for the synthesis of these dendrimers. The peripheries of the dendrimers contained 6, 12, and 24 amino groups, for the first, second, and third generation, respectively. Materials were characterized by FTIR, NMR, and MALDI-TOF MS spectrometry. These dendrimers were soluble in amide solvents, THF and acetone and displayed fluorescence maxima in the 440-500 nm range with relatively narrow peak widths indicating that they had pure and intense fluorescence. These dendrimers form chargetransfer (CT) complexes with electron acceptor molecules such as 7,7,8,8,-tetracyanoquino-dimethane and 1,1,2,2 tetracyanoethane as evidenced by UV-visible absorption spectra. V
Study of Poly(amidoamine) Starburst Dendrimers by Fluorescence Probing
Langmuir, 1997
The binding of fluorescent probe molecules to poly(amidoamine) starburst dendrimers of generations G-0, G-1, and G-2 was investigated. The solubilizing capability of these new materials, in aqueous media, increases with increasing degree of their generation. Pyrene fluorescence however undergoes significant quenching in the solubilized state. In the higher generations, G-1 and G-2, excimer fluorescence was observed even at [pyrene]/[dendrimer] ratios as low as 10-3 .
Polymer Degradation and Stability, 2006
The colouristic and fluorescent characteristics of a new composite material based on a PAMAM dendrimer of second generation whose periphery is modified with 4-N,N-dimethylaminoethylamino-1,8-naphthalimide and polyamide-6 have been investigated. This dendrimer has been investigated with regard to its application as a heterogenic sensor capable of detecting metal cations and protons in aqueous solutions. In the presence of metal cations (Ni 2þ , Fe 2þ , Fe 3þ and Co 2þ ) and protons the fluorescence intensity of the composite increases due to their coordination with dendrimer molecule. The results obtained reveal the capacity of this system to act as a sensitive sensor of environmental pollution by metal cations and protons. It has been shown that in N,N-dimethylformamide solution the metal cations inhibit the processes of photodegradation of the dendrimer.
Solvent Effect on Fluorescence Properties of Stilbene Dendrimer Surrounded by Benzyl-Ether Dendrons
Bulletin of the Chemical Society of Japan, 2015
The fluorescence maximum of the fourth generation of stilbene-cored dendrimer (trans-G4) was affected by solvent polarity. These results indicated that the core of even higher generation dendrimer was not isolated from solvent molecules and the environment of the dendrimer core is constructed by both surrounding dendron groups and penetrated solvent molecules.