Poly(9,9-dioctylfluorene) (PFO) adopts a particular type of conformation in dilute solutions of the poor solvent methylcyclohexane (MCH) below 273 K, which is revealed by the appearance of a red-shifted absorption peak at 437-438 nm. The formation of this ordered conformation depends on the temperature but is independent of polymer concentration over the range studied (3-25 µg/mL). On the basis of absorption, steadystate, and time-resolved fluorescence data, the new absorption peak at 437-438 nm is assigned to a highly ordered conformation of PFO chains, analogous to the so-called -phase first identified in PFO films. From the study of PFO solutions in MCH as a function of temperature, we conclude that these ordered segments ( -conformation) coexist with less ordered domains in the same chain. When the ordered domains are present, they act as efficient energy traps and the fluorescence from the disordered regions is quenched. The transition between the disordered and the ordered PFO conformations is adequately described by a mechanism that involves two steps: a first, essentially intramolecular, one from a relatively disordered (R) to an ordered conformation ( ), followed by aggregation of chains containing -conformation into anisotropic ordered domains. From the temperature dependence of the 437-438 nm peak intensity, the transition temperature T ) 261 K, enthalpy ∆H ) -18.0 kcal mol -1 , and entropy ∆S ) -68.4 cal K -1 mol -1 were obtained. The formation of the -conformation domains were also followed as a function of time at 260 K. The rate constants at 260 K were determined, showing an order of magnitude around 10 -3 s -1 (k Rf ) 5.9 × 10 -4 s -1 ; k fR ) 9 × 10 -4 s -1 ; k agg ) 2.3 × 10 -3 M -1 s -1 ; k diss ) 4.4 × 10 -4 s -1 ). This small magnitude explains the long times required for a "complete" conversion to the -conformation.

The discrete coagulation-fragmentation equations are a model for the kinetics of cluster growth in which clusters can coagulate via binary interactions to form larger clusters or fragment to form smaller ones. The assumptions made on the fragmentation coefficients have the physical interpretation that surface effects are important. Our results on the asymptotic behavior of solutions generalize the corresponding results of Ball, Carr, and Penrose for the Becket-Doting equation.

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Water quenches the fluorescence of methyl 9-anthroate with a rate constant showing little dependence on solvent viscosity or polarity. In dioxane, at 20 OC the value of the rate constant is 9.6 X lo6 M-' s-l , a nd the activation energy found for the process is 14.1 kJ mol-'. The quenching process is entropy-controlled and is likely to involve a hydrogen-bonded complex as an intermediate. Since the fluorescence lifetime of methyl 9-anthroate does not depend on the solvent properties other than its hydrogen-bonding ability, the concentration of nearby water can be estimated directly. Values of 3, 54, and 14 M were obtained for the solubilization site of methyl 9-anthroate in micelles of Triton X-100, sodium dodecyl sulfate (SDS), and dodecyltrimethylammonium chloride (DTAC), respectively. From the ring current effect of the anthroate group on the 'H NMR chemical shifts of the surfactant protons, it is concluded that the anthroate fluorescent probe is preferentially located in the surface region of the SDS and DTAC micelles; however, in Triton X-100, it resides in the micelle interior near the phenoxy groups of the surfactant molecule.