Origin of Strong Chiroptical Activities in Films of Nonafluorenes with a Varying Extent of Pendant Chirality

Yanhou Geng, Anita Trajkovska, Sean W. Culligan, Jane J. Ou, Huang-Ming Chen, Dimitris Katsis, Shaw H. Chen*

*Corresponding author for this work

Research output: Contribution to journalArticle

122 Scopus citations

Abstract

Novel nonafluorenes with a varying extent of pendant chirality were synthesized for an investigation of the origins of chiroptical activities in neat films. Thermal annealing of 4-μm-thick sandwiched films and of 90-nm-thick spin-cast films, all on surface-treated substrates, produced monodomain glassy films characterized as a right-handed cholesteric stack with a helical pitch length ranging from 180 to 534 nm and from 252 to 1151 nm, respectively. The observed strong circular dichroism (CD) and ge as functions of helical pitch length in single-substrate monodomain glassy cholesteric films were quantitatively interpreted with a circularly polarized fluorescence theory accounting for light absorption, emission, and propagation in a cholesteric stack. Although intertwined molecular helices were likely to be present, cholesteric stacking of rodlike molecules seemed to be the predominant contributor to the strong chiroptical activities. All the cholesteric stacks comprising a polydomain glassy film on an untreated substrate were found to contribute to CD and ge largely to the same extent as in a monodomain film. A circularly polarized blue organic light-emitting diode containing a nonafluorene film resulted in a ge of 0.35 with a luminance yield of 0.94 cd/A at 20 mA/cm2, the best performance to date.

Original languageEnglish
Pages (from-to)14032-14038
Number of pages7
JournalJournal of the American Chemical Society
Volume125
Issue number46
DOIs
StatePublished - 19 Nov 2003

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