The Synthesis and Glass-Forming Properties of Phthalocyanine-Containing Poly(aryl ether) Dendrimers

Abstract

The synthesis, structural characterisation and properties of a number of phthalocyanine-containing dendrimers are described. Peripheral substitution of phthalocyanine (Pc) with four poly(aryl ether) dendritic wedges (1st, 2nd or 3rd generation) produces materials whose properties are dominated both by the columnar self-association of the Pc core and by the glass-forming character of the dendritic substituents. Asymmetric Pcs containing a single poly(aryl ether) dendron display a columnar mesophase, the structure of which can be frozen into an anisotropic glass at room temperature. Placing the dendritic wedges at the axial sites of silicon phthalocyanine prohibits self-association and gives materials from which can be fabricated robust, isotropic solid solutions of Pc with high glass transition temperatures. A single crystal X-ray diffraction analysis of one of these compounds illustrates the ability of the axial dendrons to prevent cofacial aggregation in the solid state.

Solution and Thin‐Film Aggregation Studies of Octasubstituted Dendritic Phthalocyanines

“…The increase of peripheral dendron size decreases the ability of the Pc to aggregate. When compared to previous reports, octasubstituted second‐generation Pc 3b shows less thin‐film aggregation than a tetrasubstituted third‐generation Pc prepared by McKeown and coworkers 22 . Tetrasubstituted second‐generation dendrimer 9 exhibited a similarly split Q‐band, indicating an intermediate level of aggregation in this sample.…”

“…To compare the effect of four versus eight dendritic substituents on Pc aggregation, 22,23 we prepared tetrasubstituted dendritic phthalocyanine 9 (). Unsubstituted second‐generation dendron bromide was allowed to react with an excess of hydroquinone ( 5 , 4 equiv) along with potassium carbonate (10 equiv) and 18‐crown‐6 (0.2 equiv) in refluxing acetone.…”

“…Tetrasubstituted second‐generation dendrimer 9 exhibited a similarly split Q‐band, indicating an intermediate level of aggregation in this sample. Interestingly, a completely analogous dendritic Pc lacking the hydroquinone linker was reported to be aggregated in the condensed phase, 22 suggesting that the presence of the linker seems to prevent full aggregation of the Pc. In contrast, third‐generation 3c exhibited a complete lack of aggregation in the solid state as shown by the presence of a Q‐band, similar to that seen in dilute solution absorption spectra (Fig.…”

“…McKeown and coworkers, 20–24 Ng and coworkers, 25–28 Kobayashi and coworkers, 29,30 and Kasuga and coworkers 31,32 have studied the placement of bulky groups along the periphery of Pc chromophores or as axial substituents. Four peripheral dendritic substituents, unless coupled with electrostatic repulsion, 25,26,29,30 are ineffective at preventing Pc self‐association, even up to third‐generation dendrimers 20–24 . Axial dendritic substituents attached to the central atom of a SiPc effectively prevented aggregation 23,24 .…”

Novel water‐soluble metallophthalocyanines supported on cotton fabric

“…Alkyl, alkoxy and alkylthio chains or bulky groups are bonded to peripheral and axial sites of phthalocyanines to strongly enhance their solubility [4][5][6][7][8][9][10]. Alkyl, alkoxy and alkylthio chains or bulky groups are bonded to peripheral and axial sites of phthalocyanines to strongly enhance their solubility [4][5][6][7][8][9][10].…”