Thiophene-Based Conjugated Polymers with Photolabile Solubilizing Side Chains

Abstract

This paper describes a series of thiophene-based conjugated polymers that become insoluble upon irradiation with ultraviolet light. Stille or Suzuki reactions of appropriately substituted 2,5-bromothiophene derivatives yielded terthiophene and polythiophene derivatives with either o-nitrobenzyl (ONB) ester or ONB ether photolabile side chains with n-octyl substituents. Light-induced cleavage of these ONB side chains with ultraviolet light at 365 nm cleaves the octyl chains responsible for solubilization of the polymers away from the conjugated main chains, rendering them insoluble. Consistent with the accepted mechanism of ONB photolysis, those structural modifications that would yield a more stable benzylic radical methyl substitution on the benzylic position, replacement of the ester with an ether, or bothyielded more efficient photolyses as determined by (i) quantum yields of photolysis of ONB-substituted terthiophenes, and (ii) the percentage of polymer that persists in UV-irradiated thin films upon rinsing with chloroform. These polymers behave as negative-tone photoresists, enabling both direct photopatterning of conjugated polymers, and fabrication of multilayer conjugated polymer films by irradiating with UV light after each spin-casting step. Although hole-mobility values of these polymers in thin film transistors were only ∼10 −5 cm 2 V −1 s −1 , photolysis and rinsing did not cause significant degradation in performance.

Formal preparation of regioregular and alternating thiophene–thiophene copolymers bearing different substituents

“…We have also engaged in the design of the side chain of polythiophenes, and several functionalities have been successfully introduced [12][13][14]. We further focused on the copolymerization of thiophene, employing differently substituted thiophene monomers, with which several copolymerizations are plausible, giving thiophene-thiophene copolymers of random (statistical) [15], gradient [16,17], block [18,19], alternating [20][21][22][23], etc. [24,25] makeup.…”

Stimuli-responsive side chains for new function from conjugated materials

“…[45] We therefore prepared terthiophene oligomers (Figure 5a) and analogous polymers that vary in the structure of ONB leaving group-as either carboxylic acids or phenols, and the substitution in the benzylic positions-either as methylenes or methines. [46] The trend of quantum yield of photolyses of the terthiophene derivatives in chloroform, determined using 1 H NMR spectroscopy and chemical actinometry, followed the expected trend ( Figure 5). Note that these quantum yields are corrected for the competitive absorbance of the conjugated backbone and reflect the efficiency of photolysis only taking into consideration those photons absorbed by the ONB group.…”

Aqueous Processing for Printed Organic Electronics: Conjugated Polymers with Multistage Cleavable Side Chains

“…o -Nitrobenzyl groups have been commonly used by polymer chemists to create controlled cleavage points, 19 and have recently been used by the Thomas group to create UV patternable polythiophene photoresists. 20 In combination, these reactive functionalities provide the organic soluble P(T3-MS)-O with the ability to transition to an aqueous soluble polyelectrolyte, P(T3-MS)-PE, and then transition to an insoluble polymer P(T3-MS)-I following UV irradiation.…”