Beads on a Chain (BoC) Polymers with Model Dendronized Beads. Copolymerization of [(4-NH2C6H4SiO1.5)6(IPhSiO1.5)2] and [(4-CH3OC6H4SiO1.5)6(IPhSiO1.5)2] with 1,4-Diethynylbenzene (DEB) Gives Through-Chain, Extended 3-D Conjugation in the Excited State That Is an Average of the Corresponding Homopolymers

The general objectives of the work reported here and in accompanying papers are to identify optimal tools for the synthesis of silsesquioxane (SQ)-based BoC oligomers and polymers, especially those that show 3-D, through-chain (cage) conjugation in the excited state. Here we first examine the utility of polymerizing (p-IPhSiO1.5)(8) with divinylbenzene (DVB) using Heck catalytic cross-coupling as baseline systems for BoCs with model dendrons. Thereafter, we functionalize the remaining IPh groups by cross-coupling with 4-MeOC6H4CH=CH2 or 4-NH2C6H4CH=CH2. As an alternate approach, we first functionalize (p-IPhSiO1.5)(8) with 4-MeOC6H4CH=CH2 or 4-NH2C6H4CH=CH2 by catalytic cross-coupling such that only an average of two iodophenyls remain and then polymerized with DVB or 1,4-diethynylbenzne (DEB). This latter approach permits synthesis of copolymers as demonstrated using 1:1 mixtures of the two SQs with R = NH2 or OMe. Here we assess the utility of two different routes to conjugated BoC polymers. Investigation of the UV-vis absorption and emission properties of these BoCs indicates the DVB polymers exhibit no emission red-shifts because a significant portion of the DVB used is the 1,3-isomer. However, the DEB polymers reveal nm red-shifts and charge transfer (CT) behavior, suggesting electronic interactions between SQ cages through the conjugated, bridging moieties. DEB copolymers with R = NH2- and MeO- stilbene functional groups on the cages show red-shifts intermediate between the red-shifts of the simple homopolymers, rather than independent emissions from both units as would obtain with a physical mixture again supporting electronic communication along the polymer chains and through the cages via the conjugated linkers.