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Observation of the beta-phase in two short-chain oligofluorenes

Tsoi, W. C. T. ; Charas, A. ; Cadby, A. J. C. ; Khalil, G. K. ; Adawi, A. M. A. ; Iraqi, A. I. ; Hunt, B. H. ; Morgado, J. ; Lidzey, D. L.

Advanced Functional Materials Vol. 18, Nº 2, pp. 600 - 606, February, 2008.

ISSN (print): 1616-301X
ISSN (online):

Scimago Journal Ranking: 4,27 (in 2008)

Digital Object Identifier: 10.1002/adfm.200700530

The polymer poly(9,9-dioctylfluorene) (PF8) can be driven into a morphological form termed the -phase that has enhanced planarity and increased structural rigidity. We show that the -phase can be generated in two different fluorene oligomers; a fluorene pentamer, and a short (statistical) oligomer composed of chains having a maximum length of 19 monomer units. By comparing the energy of the zero-zero phonon line in fluorescence from the -phase oligomers with that in the PF8 polymer, we show that the electronic conjugation length of the -phase is (30 ± 12) monomer-units, a value consistent with the persistence length of the molecular chain.