No abstract

High cis content (81-99%) cis-transoidal polyphenylacetylene (PPA) jacketed with amphiphilic self-assembling dendrons, poly[(3,4-3,5)mG2-4EBn] with m = 8, 10, 12, 14, 16, and (S)-3,7-dimethyloctyl, were synthesized by Rh(C triple bond CPh)(nbd)(PPh(3))(2) (nbd = 2,5-norbornadiene)/N,N-(dimethylamino)pyridine (DMAP) catalyzed polymerization of macromonomers. The resulting cylindrical PPAs self-organize into hexagonal columnar lattices with intracolumnar order (Phi(h)(io)) and without (Phi(h)). The polymers with m = 12, 14, and 16 exhibit also a hexagonal columnar crystal phase (Phi(h,k)). The reversible Phi(h,k)-to-Phi(h)(io)-to- Phi(h) phase transition in these dendronized PPAs was analyzed by a combination of differential scanning calorimetry and small and wide-angle X-ray diffraction experiments performed on powder and oriented fibers. In the Phi(h,k) and Phi(h)(io) phases, the dendronized PPAs form helical porous columns. The helical pore disappears in the Phi(h) phase. This change is accompanied by a decrease of the external column diameter that is induced by stretching of the polymer backbone along the axis of the cylinder. The helix sense of the porous PPA is selected by homochiral alkyl dendritic tails. This transition is generated by an unprecedented conversion of the PPA backbone from the cis-cisoidal conformation in the Phi(h,k) and Phi(h)(io) phases to the cis-transoidal conformation in the Phi(h) phase. Under the same conditions, the pristine cis-PPA undergoes cis-trans isomerization and irreversible intramolecular 6pi electrocyclization of 1,3-cis,5-hexatriene sequences followed by chain cleavage. These processes are eliminated in the dendronized cis-PPA below its decomposition temperature.

The synthesis of 2‐ethynyl‐9‐substituted carbazole and 3‐ethynyl‐9‐substituted carbazole monomers containing first‐generation chiral and achiral dendritic (i.e., minidendritic) substituents, 2‐ethynyl‐9‐[3,4,5‐tris(dodecan‐1‐yloxy)benzyl]carbazole (2ECz), 3‐ethynyl‐9‐[3,4,5‐tris(dodecan‐1‐yloxy)benzyl]carbazole (3ECz), 2‐ethynyl‐9‐{3,4,5‐tris[(S)‐2‐methylbutan‐1‐yloxy]benzyl}carbazole (2ECz*), and 3‐ethynyl‐9‐{3,4,5‐tris[(S)‐2‐methylbutan‐1‐yloxy]benzyl}carbazole (3ECz*), is presented. All monomers were polymerized and copolymerized by stereospecific polymerization to produce cis‐transoidal soluble stereoisomers. A structural analysis of poly(2ECz), poly(2ECz*), poly(3ECz), poly(3ECz*), poly(2ECz*‐co‐2ECz), and poly(3ECz*‐co‐3ECz) by a combination of techniques, including 1H NMR, ultraviolet–visible, and circular dichroism spectroscopy, thermal optical polarized microscopy, and X‐ray diffraction experiments, demonstrated that these polymers had a helical conformation that produced cylindrical macromolecules exhibiting chiral and achiral nematic phases. Individual chains of these cylindrical macromolecules were visualized by atomic force microscopy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3509–3533, 2002

Novel chelators, i.e., 4-(2-pyridyl)-1,2,3-triazole derivatives, were synthesized by means of Cu(I)-catalyzed 1,3-dipolar cycloaddition and used to prepare luminescent Re(I) complexes [ReCl(CO)(3)(Bn-pyta)], [ReCl(CO)(3)(AcGlc-pyta)] and [ReCl(CO)(3)(Glc-pyta)] (Bn-pyta = 1-benzyl-4-(2-pyridyl)-1,2,3-triazole, AcGlc-pyta = 2-(4-(2-pyridyl)-1,2,3-triazol-1-yl)ethyl 2,3,4,6-tetra-O-acetyl-beta-d-glucopyranoside, Glc-pyta = 2-(4-(2-pyridyl)-1,2,3-triazol-1-yl)ethyl beta-d-glucopyranoside). X-Ray crystallography of Bn-pyta and Glc-pyta indicated an azocompound-like structure while the 1,2,4-triazole isomer has an azine character. [ReCl(CO)(3)(Bn-pyta)] crystallized in the monoclinic system with space group P2(1)/n. Bn-pyta ligand coordinates with the nitrogen atoms of the 2-pyridyl group and the 3-position of 1,2,3-triazole ring, which is a very similar coordinating fashion to that of the 2,2'-bipyridine derivative. The glucoconjugated Re(I) complexes [ReCl(CO)(3)(AcGlc-pyta)] and [ReCl(CO)(3)(Glc-pyta)] hardly crystallized, and were analyzed by applying extended X-ray absorption fine structure (EXAFS) analysis. The EXAFS analyses suggested that the glucoconjugation at the 1-position of the 1,2,3-triazole makes no influence to the coordinating fashion of 4-(2-pyridyl)-1,2,3-triazole. [ReCl(CO)(3)(Bn-pyta)] showed a blue-shifted maximum absorption (333 nm, 3.97 x 10(3) M(-1) cm(-1)) compared with [ReCl(CO)(3)(bpy)] (371 nm, 3.35 x 10(3) M(-1) cm(-1)). These absorptions were clearly assigned to be the mixed metal-ligand-to-ligand charge transfer (MLLCT) on the basis of time-dependent density functional theory calculation. The luminescence spectrum of [ReCl(CO)(3)(Bn-pyta)] also showed this blue-shifted feature when compared with that of [ReCl(CO)(3)(bpy)]. The luminescence lifetime of [ReCl(CO)(3)(Bn-pyta)] was determined to be 8.90 mus in 2-methyltetrahydrofuran at 77 K, which is longer than that of [ReCl(CO)(3)(bpy)] (3.17 micros). The blue-shifted electronic absorption and elongated luminescence lifetime of [ReCl(CO)(3)(Bn-pyta)] suggested that 4-(2-pyridyl)-1,2,3-triazole functions as an electron-rich bidentate chelator.

A library of eleven high cis-content cis-transoidal polyphenylacetylenes (PPAs) dendronized with self-assembling dendrons was prepared from a library of fifteen convergently synthesized macromonomers. Using [Rh(C triple bond CPh)(nbd)(PPh(3))(2)] (nbd=2,5-norbornadiene) in the presence of 10 equiv of N,N-dimethylaminopyridine, predictive control over molecular weight and narrow molecular weight distribution are obtained. The PPA backbone serves as a helical scaffold for the self-assembling dendrons. The dendron primary structure dictates the diameter of the cylindrical PPAs in bulk, both in the self-organized hexagonal columnar (Phi(h)) lattice determined by X-ray diffraction (XRD) and in monolayers on highly ordered pyrolytic graphite (HOPG) and mica visualized by atomic force microscopy (AFM). Thermal and bulk phase characteristics of the cylindrical PPAs reinforces the generality that flexible polymer backbones adopt a helical conformation within the cylindrical macromolecules generated by polymers jacketed with self-assembling dendrons.

Self-organization of individual dendronized poly(phenylacetylene) (PPA) macromolecules on highly oriented pyrolytic graphite (HOPG) is revealed by atomic force microscopy (AFM). The dendronized PPA is composed of amphiphilic, self-assembling dendrons. Individual macromolecules are imaged as oblate cylindrical objects whose relative orientation in the first layer adsorbed to the HOPG reflects underlying lattice symmetry. This is due to epitaxial adsorption of the peripheral alkyl tails. Thermal annealing results in large domains of uniformly oriented dendronized PPAs (i.e., 2D nematic order) due to intermolecular interactions. Periodicity within domains and between layers is dictated by the height and width of the oblate cylindrical PPA. A further consequence of epitaxy is that at the HOPG interface the PPA backbone adopts a more extended conformation than the helical cis−cisoidal conformation of the internally ordered hexagonal columnar ( ) phase found in bulk. Well-ordered domains of cylindrical helical dendronized PPAs offer the potential to exploit single-handed helical chirality at the HOPG surface.

5,10,15,20-Tetrakis(4-(2,3,4,6-tetra-O-acetyl-beta-d-glucopyranosylthio)-2,3,5,6-tetrafluorophenyl)porphyrin 2a and its Zn(II), Pd(II), and Pt(II) complexes 2b, 2c, and 2d were prepared in excellent yields by nucleophilic substitution of the corresponding free-base porphyrin and metalloporphyrins with acetyl 2,3,4,6-tetra-O-acetyl-1-thio-beta-d-glucopyranoside. Deprotection of 2a, 2b, 2c, and 2d by alkaline hydrolysis afforded the corresponding S-glucosylated porphyrin 3a and its metal complexes 3b, 3c, and 3d. The structures and purity of all new photosensitizers were confirmed by elemental analysis and (1)H, (13)C, and (19)F NMR, UV-vis, and steady-state luminescence spectroscopy. The relative efficiency of singlet oxygen ((1)O(2)) production increased in the order of free-base fluoroporphyrins (2a and 3a) < Zn(II) complexes (2b and 3b) < Pd(II) complexes (2c and 3c), which can be explained in terms of the heavy-atom effect, while the (1)O(2)-producing efficiency of Pt(II) complexes (2d and 3d) were exceptionally low. In vitro photocytotoxicity of these eight S-glucosylated photosensitizers was examined in HeLa cells. Although all protected photosensitizers 2a, 2b, 2c, and 2d showed no photocytotoxicity, the photosensitizers 3a, 3b, and 3c exerted potent photocytotoxicity. These results clearly indicated that the sugar moieties of 3a, 3b, and 3c act as not only water-solubility-enhancing functionalities but also cellular-uptake-enhancing elements. Photocytotoxicity testing of 3a, 3b, and 3c in the presence of reactive oxygen species inhibitors suggested that (1)O(2) is the major mediator of cell death. Hence, the Zn(II) and Pd(II) complexes 3b and 3c are promising photosensitizers having cellular uptake-facilitating units (sugar moieties) and enhanced (1)O(2) generation due to the heavy-atom effect.

Introduction of a heavy atom into photosensitizers generally facilitates intersystem crossing and improves the quantum yield (Phi(Delta)) of singlet oxygen ((1)O(2)), which is a key species in photodynamic therapy (PDT). However, little information is available about the physiological importance of this heavy-atom effect. The aim of this study is to examine the heavy-atom effect in simple metallochlorins in vitro at the cellular level. 1,3-Dipolar cycloaddition of azomethine ylide to 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato palladium(II) and platinum(II) afforded metallochlorins 4b and 4c in yields of 17.1 and 12.9%, respectively. The Phi(Delta) values increased in the order of 4a (0.28) < 4b (0.89) < 4c (0.92) in C(6)D(6). The photocytotoxicity of 4a, 4b, and 4c was evaluated in HeLa cells at a light dose of 16 J x cm(-2) with lambda > 500 nm and increased in the order of 4a < 4b < 4c at the concentration of 0.5 microM. The photocytotoxicity of 4b and 4c was significantly inhibited by addition of sodium azide, but not D-mannitol, suggesting that (1)O(2) is the major species causing cell death. Our results clearly indicate that 4b and 4c act as efficient (1)O(2) generators due to the heavy-atom effect in a cellular microenvironment as well as in nonphysiological media.