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X-ray diffraction, UV-vis absorption and photoluminescence (PL) spectroscopyhave been used to study the well-known order-disorder transition (ODT) to thebeta phase in poly(9,9-(di n,n-octyl)fluorene)) (PF8) thin film samples throughcombination of time-dependent and temperature-dependent measurements. The ODTis well described by a simple Avrami picture of one-dimensional nucleation andgrowth but crystallization, on cooling, proceeds only after molecular-levelconformational relaxation to the so called beta phase. Rapid thermal quenchingis employed for PF8 studies of pure alpha phase samples while extendedlow-temperature annealing is used for improved beta phase formation. Lowtemperature PL studies reveal sharp Franck-Condon type emission bands and, inthe beta phase, two distinguishable vibronic sub-bands with energies ofapproximately 199 and 158 meV at 25 K. This improved molecular level structuralorder leads to a more complete analysis of the higher-order vibronic bands. Anet Huang-Rhys coupling parameter of just under 0.7 is typically observed butthe relative contributions by the two distinguishable vibronic sub-bandsexhibit an anomalous temperature dependence. The PL studies also identifystrongly correlated behavior between the relative beta phase 0-0 PL peakposition and peak width. This relationship is modeled under the assumption thatemission represents excitons in thermodynamic equilibrium from states at thebottom of a quasi-one-dimensional exciton band. The crystalline phase, asobserved in annealed thin-film samples, has scattering peaks which areincompatible with a simple hexagonal packing of the PF8 chains.Comment: Submitted to PRB, 12 files; 1 tex, 1 bbl, 10 eps figure

physical review. b, condensed matter

Structure, photophysics, and the order-disorder transition to the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>β</mml:mi></mml:math>phase in poly(9,9-(di-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi><mml:mo>,</mml:mo><mml:mi>n</mml:mi></mml:math>-octyl)fluorene)

Structure, photophysics, and the order-disorder transition to theβphase in poly(9,9-(di-n,n-octyl)fluorene)