Synthesis and characterization of new copolymers based on fluorenylidene-linked conjugated oligo(p-phenylene)s

Abstract

A group of alternating, thermally stable, fluorescent copolymers consisting of fluorenylidene‐linked conjugated oligo(p‐phenylene) segments is presented. The copolymers have been prepared by the palladium‐catalyzed Suzuki polycondensation method. Analogous model compounds have been also prepared. The copolymers obtained are found to be soluble and easily processable from conventional organic solvents such as chloroform and have been characterized by 1H and 13C NMR spectroscopy, FT‐IR spectroscopy and elemental analysis. The degree of polymerization has been estimated by gel permeation chromatography (GPC). The thermal properties of the copolymers have been characterized by differential scanning calorimetry (DSC). The results obtained by UV/VIS spectroscopy indicate that electronic properties can easily be tailored by a variation of the length and structure of the chromophore unit and are independent of the length of the polymer main chain.

New Polymers Based on Fluorenylidene-Linked Conjugated Oligo(p-phenylene)s

“…The 9,9-bis(4-bromophenyl)fluorene (2) [10] and 2,5-bis(alkoxy)-1,4-phenylene diboronic acids (8,9) [15] were prepared as described in literature. N N N , 15: ---, copolymer with only one alkoxy-substituted phenylene unit: [10] -. under nitrogen at -78 8C 2.5 equivalent amounts (32 mL, 51 mmol) of butyl lithium (1.6 m solution in hexane) were slowly added.…”

“…[10] The 9,9-bis(4-bromophenyl)fluorene (A 2 -type monomer) and various aromatic bis(boronic ester)s (B 2 -type monomers) were the key structures to realize this concept. In this work, in the synthesis of polymers, fluorenylidene-linked p-pentaphenyl repeating units with lateral substituents on the three middle phenylene rings were introduced in order to improve the processability of the polymers.…”

“…The dibromide 2 was prepared from the corresponding commercially available diamine 1 by a classical Sandmeyer procedure. [10] As shown in Scheme 1 the synthesis of the corresponding 1,3-propanediol diester of p-phenylene diboronic acid 3 can be achieved by a lithium-halogen exchange with two equivalents of butyllithium in diethyl ether at -78 8C followed by reaction with trimethyl borate and esterification with 1,3-propanediol. [15] Compound 3 was isolated in 37% yield.…”

“…By using comonomers containing three phenylene rings, which are all substituted with flexible side chains, it was possible to increase the solubility of the resulting copolymer compared to analogous copolymer with only one substituted phenylene unit described in our previous work. [10] The polymers were obtained by precipitation from methanol. The polymerizations resulted in yields of approximately 80%.…”

“…Recently, we showed the synthesis of new conjugated alternating copolymers containing oligo(p-phenylene) units of well-defined size and structure as isolated conjugated chromophores in the main chain. [10] The following factors were taken into account concerning the construction of the polymers: (i) the number of paralinked phenylene rings (the extended delocalization lengths of most fully conjugated polymers results in small electronic band gaps and red-shifted emission); (ii) the interruption of the conjugation by incorporating non-conjugated segments into the polymer main chain [11 -21] (the effective conjugation length can be controlled); (iii) the attachment of long and flexible side chains to the polymer backbone [22 -25] (the solubility is improved whereas the pconjugation of the chain can be severely disturbed by the enhanced twist angle inferred by the side groups); (iv) the substitution of the main chain with electron-donating substituents [25,26] (the electron density along the polymer backbone could be tuned in this fashion). We introduced the sp 3 -carbon atoms of the fluorene units in order to limit the extension of the delocalized p-electron system by interruption of the conjugation between oligo(p-phenylene) chromophores in the polymer backbone.…”