Singlet molecular oxygen ( 'Ago2) has been created, by energy transfer, from a triplet-state photosensitizer in a variety of solid organic polymers. In independent time-resolved experiments, the phosphorescence of 'Ago2 and the absorbance of the sensitizer triplet state were monitored as a function of the sample temperature, matrix rigidity, and molecular composition. In more glassy samples, the time-dependent behavior of the ' Agoz phosphorescence signal is strikingly different from that observed in liquid analogues, exhibiting long decay times with non-first-order kinetics. As the polymer matrix is made leas glassy, however, either by an increase in temperature or by using copolymers or low molecular weight additives, the lAg02 phosphorescence signal appearance and disappearance rates increase, approaching rates observed in liquid solvent analogum. At this limit, the '$02 decay follows fmborder kinetics. The triplet sensitizer flash absorption data indicate that, in the glassy organic polymers, the time-dependent behavior of the 1$02 phosphorescence signal principally reflects that of its precursor. Deconvolution of the sensitizer decay from the experimentally observed (or manifest) 'Ago2 phosphorescence signal yields intrinsic 'Ago2 lifetimes which, to a first-order determination, are independent of temperature and matrix rigidity and are approximately equivalent in magnitude to those recorded in liquid-phase analogues. In this convolution integral, it is necessary to incorporate a model in which the 'Ago2 sensitizer exists in a distribution of nonequivalent sites in the polymer matrix.Data obtained from a perdeuterated polymer give an intrinsic 'Ago2. lifetime that is an order of magnitude longer compared with that obtained from a perprotiated analogue and indicate that a solid-phase matrix exerts control over the intrinsic rate of 'Ago2 deactivation in a way very similar to that in liquid-phase systems.

The quenching of singlet molecular oxygen ('AgOz) by 1,4-diazabicyclo [2.2.2] octane (DABCO), triphenylamine (TPA), and nickel(II) bis [diisopropyl dithiophosphate] (N) was studied in solid polystyrene (PS) and poly(methyl methacrylate) (PMMA). Quenching rate constants (kq) were determined by monitoring the time-resolved 1 8 2 phosphorescence as a function of quencher concentration in photosensitized experiments. For the efficient quencher N and the moderately efficient quencher DABCO, the rate constants determined in the polymers are smaller than those determined in liquid-phase analogs [fcq(PMMA) < feq(PS) < Aq(liquid)]. Moreover, the solids have a "leveling effect" on the N and DABCO rate constants, minimizing differences in kq that are quite pronounced in the liquid. These observations track a decrease in the oxygen diffusion coefficient [Dq(PMMA) < Dq(PS) < Do(liquid)] and are consistent with a quenching process in the polymer that is principally controlled by solute diffusion to form the 1Ag02~quencher encounter pair. For the poorer quencher TPA, however, where the rate of quenching is determined more by events in the 1Ag02quencher encounter pair than by solute diffusion, feq(PMMA) > fcq(PS) > ^(liquid). These data are consistent with an increase in the number of collisions between the quencher and xAgC>2 in the more rigid solvent cage of the solid polymer. Because differences between fcq(polymer) and Aq(liquid) will vary greatly as a function of the quencher efficiency, published attempts to define the role of1 AgC>2 in a mechanism of polymer degradation may need reinterpretation; specifically, the common practice of comparing values of feq(liquid) with parameters that reflect photodegradation in quencher-doped polymers may be misleading.

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A synthetic approach to grandisol is described. The route to the cyclobutane core relies on an efficient intramolecular [2+2] cyclo­addition that establishes the required cis-ring fusion at the adjacent side chains of the cyclobutane ring. Using a new two-step lithium/halide homologation procedure, norgrandisol was efficiently converted into grandisol. This new approach enables the synthesis of grandisol in five steps from commercially available starting material in 22% overall yield.