Localized versus Backbone Fluorescence in N-p-(Diarylboryl)phenyl-Substituted 2,7-and 3,6-Linked Polycarbazoles

The triarylborane acceptor in poly[9-((4-dimesitylboryl)-3,5-dimethylphenyl)-9H-carbazole]-3,6-diyl P2 has a strong impact on the optical properties of this 3,6-linked carbazole main chain polymer and results in an enhanced fluorescence quantum yield because of a low-lying fluorescent CT state. In contrast, the same acceptor substituent does not influence the optical properties of poly [9-((4-dimesitylboryl)-3,5-dimethylphenyl)-9H-carbazole]-2,7-diyl P1. In the latter polymer, the optical properties are governed by conjugation along the carbazole backbone. This interpretation is supported by comparison with poly[9-(4-(diphenylmethyl)-phenyl)-9H-carbazole]-2,7-diyl P3, which serves as a reference polymer. Synthesis and characterization by gel permeation chromatography, NMR spectroscopy, absorption, and fluorescence measurements in solution and solid state and cyclic voltammetric Measurements of the three polymers are presented.