Cyclobutadienes polymers

Bunz et al. explored the possibility of doping PPE chains covalently with small amounts of fluorescence-quenching cyclobutadiene complexes, in order to endow their optical properties to the base polymer, PPE [80]. Due to their extensive experience of cyclobutadiene complexes in polymer synthesis [81], the authors prepared several polymers PAE-CoCpl-5 (Table 4) containing different contents of CoCp complexes. The quantum yields were determined by simple comparison of the intensities of the emitted light to that of a standard... 

Co-free PAE). In PAE-CoCpl, the fluorescence quantum yield is only 18% of that observed for Co-free PAE, even though the quencher substitutes less than 0.1% of the aryleneethynylene units. The fluorescence in solution disappeared in PAE-CoCp4, where every fifth unit is a cyclobutadiene complex. The mechanism by which this quenching occurs is via the cobalt-centered MLCT states [82,83], conferred onto the polymer by the presence of cyclobutadiene complexes. Even in the solid state the polymers PAE-CoCpl-2 are nonemissive. It was therefore shown that incorporation of CpCo-stabilized cyclobutadiene complexes into PPEs even in small amounts leads to an efficient quenching of fluorescence in solution and in the solid state. Quenching occurs by inter- and intramolecular energy transfer [84]. 

The stabilization of iminoboranes can yield five different tj ies of products cyclodimers (1,3,2,4-diazadiboretidines, Di), cyclotrimers (borazines, Tr), bicyclotrimers (Dewar borazines, Tr ), cyclotetramers (octahydro-l,3,5,7-tetraza-2,4,6,8-tetraborocines, Te), and polymers (polyiminoboranes, Po) these substances are isoelectronic with cyclobutadienes, benzenes, Dewar benzenes, cyclooctatetraenes, and polyalkynes, respectively, which are all known to be products of the thermodynamic stabilization of alkynes. 

CoCp unit C-C bond activation, 7, 80 CoCp unit CH activation, 7, 79 in ethylene polymerization, 7, 81 substituted ligands, 7, 71 synthetic applications, 7, 74 with )4-cyclobutadiene applications, 7, 66 new ligand preparation, 7, 70 with )4-(cyclobutadiene) ligands, 7, 59 dendrimeric cobaltocenium derivatives, 7, 88 with fullerenes, 7, 51 HP-NMR and HP-IR studies, 1, 488 with rj -hydrocarbyl units, 7, 8 immobilized, as polymer support, 12, 681 kinetic studies, 1, 520 with )3-ligands, 7, 56 with metallaboranes, 3, 158 overview, 7, 1-119... 

Other chromophores were also investigated this way, example includes cyclobutadiene based doped polymer, of about 8 pm V 1 d33 nonlinearity with about 10 wt % loading, for green 532 nm generation and poled pNAn-PVA for blue 443 nm generation, in this case below the 480 nm cut-off wavelength of the material [36,37]. 

The iron phenanthroline derivative in Scheme 9 is a source of cyclobutadiene which can be trapped by maleanil. Both reactants bound to a polymer give, when oxidized, the polymeric adduct shown. By methaminolysis a derivative is formed, proving that cyclobutadiene is a free-existing intermediate in this reaction (74). 

Altmann, M. Enkelmann, V. Bunz, U.H.F. Synthesis and characterization of a novel cyclobutadiene-octatetrayne polymer. Chem. Ber. 1996, 129, 269-273. 

Bunz and co-workers reported the preparation of polymers containing cyclopentadienyl-cobalt moieties coordinated to cyclobutadiene rings, using diethylnyl and dipropynyl cyclobu-... 

The thermal reaction of cobalt polymers 148 with isocyanates at 120 °C leads to 2-pyridone-containing polymers 149 339 Yeii characterized, yellow polyesters 150 that contain skeletal (cyclobutadiene)cobalt moieties in the main... 

---