Synthesis and Characterization of Monodisperse Oligofluorenes

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Abstract
An efficient synthesis of 9,9‐bis(2‐ethylhexyl)fluorene oligomers up to the heptamer is reported, with repetitive Suzuki and Yamamoto coupling reactions employed in the synthesis. The key steps for preparation of the essential intermediates include Pd‐catalyzed transformation of aryl bromides to aryl boronic esters (Miyaura reaction) and the application of the much higher reactivity of aryl boronic esters over aryl bromides in the Pd‐catalyzed cross‐coupling reaction with aryl diazonium salts. Variation of the UV/Vis absorption and photoluminescence characteristics with chain length is reported. Moreover, glass transition and liquid‐crystal characteristics of the oligomers are described and compared with those of the polymer.