Formation of Macrocycles in the Synthesis of Poly( N ‐(2‐ethylhexyl)carbazol‐3,6‐diyl)

A series of polymerizations of 3,6‐dibromo‐9‐(2‐ethylhexyl)carbazole was carried out in different monomer concentrations using standard Yamamoto reaction conditions. It was found that the molecular weight of the resulting poly( N ‐(2‐ethylhexyl)carbazol‐3,6‐diyl) strongly depends on the monomer concentration in the reaction mixture. Matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) measurements confirmed the formation of low‐molar‐mass cyclic oligomers of the 3,6‐disubstituted carbazole. In this paper we describe, for the first time, the formation of large amounts of a cyclic tetramer and of higher macrocycles in the synthesis of poly( N ‐alkyl‐3,6‐carbazoles) by the Yamamoto method. This seems to be a limiting factor in the synthesis of high molecular weight poly( N ‐alkyl‐3,6‐carbazole)s. The optical, thermal, and electrochemical properties of poly( N ‐(2‐ethylhexyl)carbazol‐3,6‐diyl) have been investigated. Poly( N ‐(2‐ethylhexyl)carbazol‐3,6‐diyl) is thermally stable, with 5% weight loss at 460 °C in nitrogen. The polymer exhibits a weak blue fluorescence with a maximum at 425 nm. Poly( N ‐(2‐ethylhexyl)carbazol‐3,6‐diyl) is electrochemically stable, its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are −5.0 and −1.6 eV, respectively.