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The alkyne-functionalized Frechet-type dendrons 2-Dm containing benzamine were synthesized by N-alkylation of the corresponding dendritic benzyl chlorides with 4-ethynylaniline. The oxidative homo-coupling reaction of the alkyne-functionalized Frechet-type dendrons 2-Dm was allowed to provide the first through fourth generation dendrimers 3-Gm with 1,4-diphenylbuta-1,3-diynes at chromophore core in high yields. Their structure of dendrimers was confirmed by 1H and 13C NMR spectroscopy, IR spectroscopy, mass spectrometry, and GPC analysis. The photophysical properties of the synthesized dendrimers was investigated.

Graphical AbstractEfficient double click methods for the synthesis of carbazole core diblock codendrimers were developed. The synthetic strategy involved the sequential double click reactions between an alkyne and an azide. The chromophore building block, N-octyl-3,6-diazidocarbazole, was chosen to serve as the azide functionalities for dendrimer growth via double click reactions with the alkyne-functionalized PAMAM dendrons as hydrophilic dendron and alkyne-functionalized Frechet-type dendrons as hydrophobic dendron. The structure of diblock codendrimers was confirmed by 1H- and 13C-NMR spectroscopy, IR spectroscopy, mass spectrometry, and GPC analysis.

Graphical AbstractGeneral, fast, and efficient fusion methods for the synthesis of dendrimers with 1,4-diphenylbuta-1,3-diyne at a core were developed. The synthetic strategy was employed the fusion method of the terminal alkyne via CuI/NBS/DIPEA-mediated Glaser-type coupling reaction. Glaser-type coupling reaction under CuI/NBS/DIPEA promoting system could be completed under ambient temperature without exclusion of air and moisture. The fusion of the terminal alkyne-focal Frechet-type dendrons 3-Dm by homo-coupling of terminal alkyne lead to the formation of symmetric Frechet-type dendrimers 4-Gm with 1,4-diphenylbuta-1,3-diyne at core. Their structure of dendrimers was confirmed by 1H- and 13C-NMR spectroscopy, IR spectroscopy, mass spectrometry, and GPC analysis.

Donor–acceptor interactions or charge transfer (CT) interactions are an important class of non-covalent interactions and have been widely exploited in self-assembling systems. Beyond molecular chemistry, supramolecular chemistry aims at constituting highly complex, functional chemical systems from components held together by intermolecular forces. Chemosensors are the molecules of abiotic origin that bind selectively and reversibly with the analyte with concomitant change in one or more properties of the system. The recognition and signaling of ionic and neutral species of varying complexity is one of the most intensively studied areas of contemporary supramolecular chemistry. Among different types of chemosensors, colorimetric/chromogenic chemosensors are especially attractive because the guest determination can be carried out by the naked eye, without the use of expensive equipment and they also find direct applications in the development of optodes and disposable dip-stick arrays based on absorption changes. Although molecules containing an electron donor and an electron acceptor linked by a spacer have also been studied extensively in conjunction with the development of stable intramolecular CT complex, to the best of our knowledge, there is no report to sense the analyte using molecules containing an electron donor and an electron acceptor linked by a spacer. In continuation with our research on the selfassembling supramolecular systems via donor–acceptor interactions, we were intrigued to apply this interaction for signaling of ionic species. Herein we report on the design and synthesis of U-shape molecule which is linked by oligoethylene glycols (OEGs) between an electron-deficient (methyl viologen; MV) and an electron-rich (2,6-dialkoxynaphthalene; Np) units and their application on sensing metal ion (Figure 1).

E-mail: shjin@pusan.ac.krReceived December 5, 2012, Accepted December 18, 2012Key Words : Alkyne, Azide, Carbazole, Click chemistry, PAMAM DendrimerDendrimers, which are prepared by repetition of a givenset of reactions using either divergent or convergent strate-gies, are highly branched and regular macromolecules withwell-defined structures.

E-mail: jihyeon@gachon.ac.krReceived September 9, 2012, Accepted September 24, 2012Efficient double click methods for the synthesis of diblock codendrimers were developed. The syntheticstrategy involved the sequential click reactions between an alkyne and an azide. The short core building block,1,4-diazidobutane, was chosen to serve as the azide functionalities for dendrimer growth via click reactionswith the alkyne-functionalized PAMAM dendrons as hydrophilic dendron and alkyne-functionalized Frechet-type dendrons as hydrophobic dendron. The structure of diblock codendrimers was confirmed by

E-mail: shjin@pusan.ac.krReceived May 23, 2012, Accepted July 7, 2012Key Words : Alkyne, Azide, Carbazole, Click chemistry, DendrimerDendrimers, which are prepared by repetition of a givenset of reactions using either divergent or convergentstrategies, are highly branched and regular macromoleculeswith well-defined structures and have served as functionalobjects in nanotechnology and nano-materials science.

E-mail: jihyeon@gachon.ac.krReceived June 10, 2012, Accepted July 31, 2012Key Words : Alkyne, Azide, ABA triblock, Click chemistry, DendrimerDendrimers, which are prepared by repetition of a givenset of reactions using either divergent or convergent strategies,are highly branched and regular macromolecules with well-defined structures

A synthetic strategy for dendrimers was developed using Staudinger/aza-Wittig reaction with an aldehyde and an azide in the presence of triphenylphosphine, followed by the reduction of imine intermediates. A fusion method between Frechet-type dendritic benzaldehydes and Frechet-type dendritic benzyl azides led to the formation of first-through fourth-generation dendrimers containing secondary amine as a connector in high yields. Further, fusion coupling using different generation dendrons afforded, efficiently, the unsymmetrical dendrimers. The obtained dendrimers were characterized by the analyses of 1H and 13C NMR spectroscopy, IR spectroscopy, mass spectra, and gel permeation chromatography (GPC) analysis.

Efficient stitching methods for the synthesis of Frechet-type dendrimers with linear PEG units at a core were elaborated. The synthetic strategy involved an inexpensive 1,3-dipolar cycloaddition reaction between an alkyne and an azide in the presence of Cu(I) species which is known as the best example of click chemistry. The linear core building blocks, two diazido-PEG units, were chosen to serve as the azide functionalities for dendrimer growth via click reactions with the alkyne-dendrons. These two building blocks were employed together with the alkyne-functionalized Frechet-type dendrons in a convergent strategy to synthesize two kinds of Frechet-type dendrimers with different linear core units.

dendrimers. 2 The convergent methodology installs the core in the final step, enabling the incorporation of functionalities. It provides greater structural control than the divergent approach due to its relatively low number of coupling reactions at each growth step. Future applications of dendrimers rely on efficient and practical synthetic procedures. Therefore, development of a versatile methodology to render the synthesis of dendrimers more adaptable to specific needs is necessary. The last decade has witnessed the rapid growth of the click chemistry which is the coppercatalyzed azide-alkyne cycloaddition reaction developed by

The convergent synthetic strategy for the emissive dendrimers having the chromophore at core via the coppercatalyzed 1,3-dipolar cycloaddition reaction between alkyne and azide was described. 2,7-Diazido-9,9-dioctyl9H-fluorene, designed to serve as the core in dendrimer, was stitched with the alkyne-functionalized Frechettype and PAMAM dendrons by the click chemistry leading to the formation of the corresponding fluorescent dendrimers in high yields. The preliminary photoluminescence studies indicated that 2,7-diazido-9,9-dioctyl9H-fluorene showed no fluorescence due to the quenching effect from the electron-rich α-nitrogen of the azido group but the dendrimers fluoresced due to the elimination of the quenching through the formation of the triazole ring.

General, fast, and efficient fusion methods for the synthesis of dendrimers with 1,3-diynes at a core were developed. The synthetic strategy was employed the oxidative homo-coupling of terminal alkyne. The oxidative homo-coupling reaction of the alkyne-functionalized Frechet-type dendrons 1-Dm was allowed to provide first through fourth generation dendrimers 2-Gm with 1,3-diynes at core. The fusion of the propargylfunctionalized PAMAM dendrons 3-Dm by homo-coupling of terminal alkyne lead to the formation of symmetric PAMAM dendrimers 4-Gm. Their structure of dendrimers was confirmed by 1 H and 13 C NMR

General, fast, and efficient stitching methods for the synthesis of dendrimers with linear PEG units at a core, as dendritic-linear-dendritic materials, were developed. The synthetic strategy involved the click reaction between an alkyne and an azide. The linear core building blocks, three dialkyne-PEG units, were chosen to serve as the alkyne functionalities for dendrimer growth via click reactions with the azide-dendrons. These three building blocks were employed together with the azide-functionalized Frechet-type dendrons in a convergent strategy to synthesize the Frechet-type dendrimers with different linear core units. Their structure of dendrimers was confirmed by 1 H and 13 C NMR spectroscopy, IR spectroscopy, mass spectrometry, and GPC analysis.

and now is known as click chemistry. This reactionhas many advantages: very high yields, mild and simplereaction conditions, oxygen and water tolerance, and easyisolation of product. In addition, it is highly chemoselective,affording 1,4-regiospecific 1,2,3-triazole even in the pre-sence of various functional groups.

E-mail: shjin@pusan.ac.krReceived August 1, 2011, Accepted August 8, 2011Frechet-type dendritic benzaldehydes were efficiently synthesized using 3,5-dihydroxybenzaldehyde as analdehyde focal point functionalized unit by adding a generation to the existing dendron or direct oxidation ofFrechet-type dendritic benzyl alcohols. These dendritic benzaldehydes were applied for the construction ofdendrimers containing secondary amines as connectors via Staudinger/ aza-Wittig Reactions with α,α'-diazido-p-xylene core.Key Words : Aldehyde, Azide, Dendrimer, Staudinger/ aza-Wittig reactionIntroductionDendrons and dendrimers are the most intensely investi-gated subset of dendritic polymers. Dendrimers, which areprepared by repetition of a given set of reactions using eitherdivergent or convergent strategies, are highly branched andregular macromolecules with well-defined structures andhave served as functional objects in nanotechnology andnanoscience.

General, fast, and efficient stitching methods are presented for the synthesis of Frechet-type dendrimers with linear units at a core, as a preliminary investigation for the synthesis of dendritic-linear-dendritic materials. The synthetic strategy involved an inexpensive, 1,3-dipolar, cycloaddition reaction between an alkyne and an azide in the presence of the Cu(I) species, which is known as the best example of click chemistry. The linear core building blocks, 1,7-octadiyne and 1,6-diazidohexane, were chosen to serve as the alkyne and azide functionalities for dendrimer growth via click reactions with the azide and alkyne-dendrons, respectively. These two building blocks were employed together with the azide- and alkyne-functionalized Frechet-type dendrons in a convergent strategy to synthesize two kinds of Frechet-type dendrimers with different linear core units. This comparative efficiency of the click methodology supports the fast and efficient synthesis of dendritic-linear-dendritic materials with the tailor made core unit.

General, fast, and efficient methods for the synthesis of Frechet-type dendrimers having core diversities were elaborated. Two core building blocks, 4,4'-(3,5-bis(propargyloxy)benzyloxy)bisphenyl and N,N,N',N'-tetra(prop-2- ynyloxycarbonylethyl)-1,2-diaminoethane, were designed to serve as the alkyne functionalities for dendrimer growth via click reactions with the azide-dendrons. The synthetic strategy involved an 1,3-dipolar cycloaddition reaction between an alkyne and an azide- functionalized Frechet-type dendrons in the presence of Cu(I) species which is known as the best example of click chemistry.

The convergent synthetic strategy for the emissive poly(benzyl ether) dendrimers having the chromophore at core via the copper-catalyzed 1,3-dipolar cycloaddition reaction between alkyne and azide was described. 2,7-Diazido-9H-fluorene, designed to serve as the core in dendrimer, was stitched with the alkyne-functionalized poly(benzyl ether) dendrons by the click chemistry leading to the formation of fluorescent poly(benzyl ether) dendrimers in high yields. The absorption and emission of the dendrimers were investigated. Their photophysical studies indicated that 2,7-diazido-9H-fluorene showed no fluorescence due to the quenching effect from the electron-rich α-nitrogen of the azido group but the dendrimers fluoresced due to the elimination of the quenching through the formation of the triazole ring.

Dendrimers are prepared by repetition of a given set of reactions using either divergent or convergent strategies. The two most widely studied dendrimer families are the Frechettype polyether and the Tomalia-type PAMAM dendrimers. The convergent approach to dendrimer synthesis introduced by Frechet and co-workers revolutionized the synthetic approaches to monodisperse dendrimers. An effective convergent synthesis requires a monomer that can undergo the activation and coupling steps in high yield. In addition, the coupling step must be very efficient to enable complete reaction. In this viewpoint, the dendritic benzylic azides are key intermediates in synthesis of the Frechet-type poly(aryl ether) dendrimers via click chemistry. In continuation with our research for the synthesis of dendrimers using click chemistry between an azide and an alkyne, there is still a demand to develop a simple, convenient, and efficient method to synthesize various dendritic benzyl azides. Here, we present a successful rapid synthesis of dendritic benzyl azides from dendritic benzyl alcohols via mesylation using methanesulfonyl chloride/Et3N and followed by in situ azidation (Scheme 1). In our method, each dendritic benzyl azide can be prepared in one pot: no isolation of intermediate mesylated dendrons is required. The key steps in the syntheses of dendritic benzyl azides were the mesylation of the hydroxymethyl group followed by the azidation with sodium azide. Furthermore, the purification of every dendritic molecule requires only solvent extraction.

Department of Chemistry and Department of Medical Bioscience, Dong-A University, Busan 604-714, Korea *E-mail: jlee@donga.ac.kr Department of Chemical & Biochemical Engineering, Dongguk University, Seoul 100-715, Korea National Creative Research Initiative Center for Smart Supramolecules, and Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea. *E-mail: kkim@postech.ac.kr Received July 5, 2007

An azide group-containing conjugated ionic polymer was synthesized by the direct polymerization of 2-ethynylpyridine and 6-azidohexyl iodide at 60 °C in methanol without any additional initiator or catalyst. This reaction proceeded well in homogeneous manner to give a moderate yield of the polymer (yield: 71%). The initial light-brown solution of 2-ethynylpyridine and 6-azidohexyl iodide became a viscous dark-red solution as the polymerization proceeded. The FT-IR spectrum of the polymer did not show the acetylenic C C bond stretching (2110 cm −1 ) and acetylenic C–H bond stretching (3293 cm −1 ) frequencies of 2-ethynylpyridine. This polymer was completely soluble in water, methanol, DMF, and DMSO, and the polymer was found to be mostly amorphous. The photoluminescence (PL) spectra of poly[ N -(6-azidohexyl)-2-ethynylpyridinium iodide] showed that the photoluminescence peak is located at 596 nm, corresponding to a photon energy of 2.08 eV.

Several diblock dendrimers were synthesized by fusion between the propargyl functionalized Frechet-type polyether and the azide functionalized Tomalia- type PAMAM dendrons. This was based on the click chemistry protocol, the copper-catalyzed cycloaddition reaction between an alkyne and an azide. The diblock dendrimers were characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and mass spectra as well as GPC analysis.

A new convergent synthetic method for the synthesis of PAMAM dendrimers has been developed. The fusion between propargyl-functionalized PAMAM dendrons and azido-functionalized PAMAM dendrons via the Cu(I)-catalyzed Huisgen [2 + 3] dipolar cycloaddition reaction (click chemistry) of an alkyne and an azide leads to the formation of symmetric PAMAM dendrimers in high yields. Furthermore, the coupling reactions between the different generation dendrons afford the size-differentiated unsymmetrical PAMAM dendrimers.

General, fast, efficient, and inexpensive methods for the synthesis of poly (amido amine) (PAMAM) dendrimers having core diversities were elaborated. In all syntheses, the major step involved an inexpensive 1,3-dipolar cycloaddition reaction between an alkyne and an azide in the presence of Cu(I) species, which is known as the best example of click chemistry. The propargyl-functionalized PAMAM dendrons are obtained by the divergent approach using propargylamine as an alkyne-focal point. Three core building blocks, 1,3,5-tris(azidomethyl)benzene, N,N,N',N'-tetra(azidopropylamidoethyl)-1,2-diaminoethane, and 4,4'-(3,5-bis(azidopropyloxy)benzyloxy)bisphenyl, were designed and synthesized to serve as the azide functionalities for dendrimer growth via click reactions with the alkyne-dendrons. These three building blocks were employed together with the propargyl-functionalized PAMAM dendrons in a convergent strategy to synthesize three kinds of PAMAM dendrimers with different core units. This novel and pivotal strategy using an efficient click methodology provides the fast and efficient synthesis of the PAMAM dendrimers with the tailed made core units.

Cucurbituril (or cucurbit[6]uril, CB[6]), a macrocycle comprising six glycoluril units, has been employed in the construction of a wide variety of interlocked molecules, and rotaxane-based molecular machines and switches. The recent discovery of cucurbituril homologues containing a different number of glycoluril units has further widened the scope of cucurbituril chemistry. In terms of cavity size, CB[6], CB[7], and CB[8] are analogous to α-, β-, and γ-CD, respectively. CB homologues share characteristic features of CB[6], such as a hydrophobic cavity, and polar carbonyl groups surrounding the portals. Therefore their varying cavity and portal sizes lead to remarkable molecular recognition properties. CB[6] forms very stable complexes with protonated diaminoalkanes (NH3(CH2)nNH3 , n = 4-7, K > 10 M) and moderately stable complexes with protonated aromatic amines such as p-methylbenzylamine (K ~3 × 10 M). On the other hand, CB[7] forms complexes with larger guest molecules that are not included in CB[6]. For example, CB[7] forms a 1 : 1 complex with 2,6-bis(4,5-dihydro-1Himidazol-2-yl)naphthalene (BDIN). It binds protonated adamantylamine as well as the methyl viologen dication (N,N'-dimethyl-4,4'-bipyridinium, MV) in a 1 : 1 ratio. Neutral molecules such as ferrocene and carborane are easily encapsulated in CB[7] in aqueous solution. The cavity of CB[8] is large enough to include two BDIN molecules to form a 1 : 2 complex, or another large macrocycle, such as cyclen and cyclam. During the course of these works, we noticed that the binding modes between the CB homologues and their guest molecules are differentiated according to the size of the hydrophobic part of the guest molecules. Herein we report the different binding interactions of CB homologues with a simple guest molecule, the 1,4-xylylenediammonium derivative 1. Depending on the cavity size of the CB, complexation led to [2] or [3]pseudorotaxanes (Figure 1).

The synthetic strategy for the convergent synthesis of emissive poly(amido amine) (PAMAM) dendrimers having the core chromophore via the copper-catalyzed 1,3-dipolar cycloaddition reaction between alkyne and azide was described. 2,7-Diazido-9H-fluorene, designed and synthesized to serve as the core in dendrimer, was stitched with the propargyl-functionalized PAMAM dendrons by the click chemistry leading to the formation of fluorescent PAMAM dendrimers in high yields. The absorption and emission of the dendrimers were investigated. Their photophysical studies indicated that 2,7-diazido-9H-fluorene showed no fluorescence due to the quenching effect from the electron-rich α-nitrogen of the azido group but the dendrimers fluoresced due to the elimination of the quenching through the formation of the triazole ring.

Department of Chemistry and Department of Medical Bioscience, Dong-A University, Busan 604-714, Korea *E-mail: jlee@donga.ac.kr Department of Chemical & Biochemical Engineering, Dongguk University, Seoul 100-715, Korea National Creative Research Initiative Center for Smart Supramolecules, and Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea. *E-mail: kkim@postech.ac.kr Received July 5, 2007

Polyamines derivatives including putrescine, spermidine and spermine derivatives and their unsymmetrical derivatives have received a great deal of attention from synthetic organic chemists 1 because of their potential use in biological activities and their presence in a number of siderophores and other natural products. 2 The protonated polyamines can interact with nucleic acids, proteins, and phospholipids. 3

E-mail: shjin@pusan.ac.krReceived July 17, 2011, Accepted July 29, 2011Key Words : Alkyne, Coupling reaction, Dendrimer, Sonogashira reactionDendrimers, which are prepared by repetition of a givenset of reactions using either divergent or convergent strate-gies, are highly branched and regular macromolecules withwell-defined structures and have served as functional objectsin nanotechnology and nanoscience.

we are fascinated to develop the new click chemistry for the construction of dendri-mers using oxidative homocoupling reaction of the terminal acetylene. In this paper, we report a feasible route to synthesize the symmetric Frechet type dendrimers from Frechet type dendrons containing alkyne moiety at their focal point by oxida-tive homocoupling of terminal alkyne. Because dendrimers contain three distinct structural parts that are the core, end-groups, and branched units connecting core and periphery, we became interested in the synthesis of self-emissive dendrimer with a fluorescent probe in core region. A relatively few applications using the alkynyl-dendron in dendrimer synthesis have been reported. The palladium-cataly-zed coupling of terminal acetylenes to aromatic bromides or iodides in basic amines have been well known since 1975.

A new ionic conjugated polyacetylene with 3rd generation dendritic benzyl moieties was easily prepared by the activated polymerization of 2-ethynylpyridine by using 3rd generation dendritic benzyl bromide. The chemical structure of polymer was characterized by various instrumental methods to have the ionic conjugated polymer system bearing 3rd generation dendritic benzyl moieties. The photoluminescence spectra of polymer showed that the photoluminescence peak is located at 516 nm, corresponding to a photon energy of 2.41 eV. The cyclovoltamograms of this polymer exhibited reversible electrochemical behaviors between the doping and undoping peaks. The kinetics of the redox process of this polymer was found that it is almost controlled by the diffusion process from the experiment of the oxidation current density of polymer versus the scan rate.

The convergent synthetic strategy for the poly(benzyl ether) dendrimers having the tetraethyleneoxide at core via the copper-catalyzed 1,3-dipolar cycloaddition reaction between alkyne and azide was described. Tetraethyleneglycol diazide, designed to serve as the core in dendrimer, was stitched with the alkyne-functionalized poly(benzyl ether) dendrons by the click chemistry leading to the formation of triblock dendritic polymers in high yields. The absorption and emission of the dendrimers were investigated. The structure of the dendrimers was characterized with 1H NMR, 13C NMR, and IR spectroscopies, mass spectra, and gel-permeation chromatography.