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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 g/mL). On the basis of absorption, steady-state, 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 () 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-1mol-1were 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 10-3s-1(k→ 5.9 × 10-4s-1; k→ 9 × 10-4s-1; kagg 2.3 × 10-3M-1s-1; kdiss 4.4 × 10-4s-1). This small magnitude explains the long times required for a “complete” conversion to the -conformation.

The functionalized flavylium salt 6-hexyl-7-hydroxy-4-methyflavylium chloride (HHMF) was employed to probe some of the fundamental features of proton transfer reactions at the surface of anionic sodium dodecyl sulfate (SDS) and cationic hexadecyltrimethylammonium chloride (CTAC) micelles. In contrast to most ordinary flavylium salts, HHMF is insoluble in water, but readily incorporates into SDS and CTAC micelles. In the ground state, the rate constant for deprotonation of the acid form (AH+) of HHMF decreases 100-fold upon going from CTAC (kd = 3.0 × 106 s-1) to SDS (kd = 1.4 × 104 s-1), consistent with the presence of an activation barrier for proton transfer in the ground state and reflecting, respectively, stabilization or destabilization of the AH+ cation by the micelle. Reprotonation of A is diffusion-controlled in both micelles (kp(SDS) = (2.1 × 1011)[H+]aq s-1 and kp(CTAC) = (3.7 × 108)[H+]aq s-1), the difference reflecting the rate of proton entry into the micelles. In the excited singlet state, the rate constants for deprotonation of the AH+* form of HHMF are similar in the two micelles (2.4 × 1010 s-1), consistent with activationless proton transfer. Reprotonation of the excited A* is dominated by fast geminate recombination of the photogenerated (A*−H+) pair at the micelle surface (krec(SDS) = 6.1 × 109 s-1 and krec(CTAC) = 3.4 × 1010 s-1) and the net efficiencies of geminate recombination are quite similar in SDS (0.89) and CTAC (0.86).