Single molecule spectroscopy of oligofluorenes: how molecular length influences polymorphism

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• 作者：Enrico Da?Como ; Esther Scheler ; Peter Strohriegl ; John M. Lupton and Jochen Feldmann
• 关键词：PACS 78.55.Kz ; 78.66.Qn
• 刊名：Applied Physics A: Materials Science & Processing
• 出版年：2009
• 出版时间：April, 2009
• 年：2009
• 卷：95
• 期：1
• 页码：61-66
• 全文大小：483.8 KB

文摘

Polyfluorene represents a unique model to study the influence of intramolecular conformation on the electronic properties of chromophores with an extended π-conjugation. According to the degree of planarity between the adjacent repeat units the electronic and optical properties can change substantially. This peculiar spectroscopic behavior has been described by identifying different phases, namely the glassy, the γ- and the β-phase. Here, we present low-temperature single-molecule spectroscopy of a series of oligofluorenes differing in the number of monomeric units, in order to gain information on the influence of chain length on the polymorphism. By monitoring the energy of the 0-0 transition we have classified single molecules belonging to the different phases. We demonstrate that a large number of molecules start to form the β-phase only when more than 9 repeat units constitute the molecular chain. The implications for the control of morphology in polyfluorene thin films are discussed.