The excitation of perchlorodiphenylmethyl radical (PDM) at 530 nm leads to the lowest excited doublet, DI ( 7 = 31 ns), from which emission is observed (a = 1 X f 0.0003). This state is quenched by electron donors and acceptors at a rate at or close to diffusion control and at much slower rates by oxygen and hydrogen atom donors. Fragmentation of PDM (ad = 0.06) occurs from a higher excited doublet (D", n 1 2) producing intermediates that are trapped by 0 2 , chlorine, or hydrogen donors, yielding products 1-6. Experimental evidence suggests a structure-photoreactivity correlation in the perchlorinated arylmethyl radicals in which the partitioning between photochemical cyclization or fragmentation depends on the twist angle between the appended phenyl rings.

Time-resolved electron paramagnetic resonance spectra of biradicals in solution with chain lengths of 3-8 carbon atoms are reported. Spin polarization arises from the spin-correlated radical pair (SCRP) mechanism and in some cases also from the triplet mechanism (TM). The observation of spectra at two magnetic fields, X-band (3375 G) and Q-band (12 500 G), provides qualitative estimates of the relative importance of each mechanism for a given biradical. The influence of several magnetic properties, such as the spin-spin coupling J, the dipolar coupling D, and the electron-nuclear hyperfine interactions aH, on the time dependence and spectral shape is discussed. The sign and magnitude of D in the precursor triplet state play a strong role in the degree of T M polarization observed in the biradical EPR spectrum. In the biradical, the ratio of J to the Zeeman energy and that of aH to J determine the sign and the magnitude of SCRP polarization. Molecular ,orbital calculations support the observation that the value of J is lowered by delocalization of electron density. The biradical also has a dipolar interaction, and it is shown how this term and the rotational orientation time 7c can contribute to spin relaxation. Observation of 1,4-bis(benzyl) and photoenol type biradicals was hindered by intermolecular reactions. The effects of conformational flexibility and tumbling on the polarization and relaxation mechanisms are discussed. The Closs biradical7 is a special case, with a triplet ground state and an encounter rate ken defined by a vibrational normal mode rather than a series of conformational jumps.

High-performance liquid chromatography (HPLC) methods for the determination of phenyl urea herbicides in water are described. The target compounds include chlortoluron, diuron, fluometuron, isoproturon, linuron, metobromuron, metoxuron, monuron, neburon, and siduron. Water was subjected to solid phase extraction (SPE) using either automated SPE with 47 mm C(18) Empore disks or on-line precolumn concentration. Herbicides were separated on a C(18) reversed phase column with an acetonitile-water gradient and were detected with either a diode array detector (DAD) or a postcolumn photolysis and derivatization (PPD) detector system. Photolysis converted the phenyl ureas to monoalkylamines that were derivatized to fluorescent isoindoles by reaction with o-phthalaldehyde and 2-mercaptoethanol. The DAD monitoring at 245 nm was linear over three decades with instrument detection limits of approximately 0.01 mg/L. SPE efficiency was between 48 and 70% in laboratory reagent water, but use of the internal standard quantitation method improved accuracy. High total dissolved solids and total organic carbon values in surface water improved recoveries relative to laboratory reagent water for all of the phenyl ureas. In Colorado River water spiked at 1 or 50 microg/L, mean recoveries ranged from 74 to 104%. Method detection limits (MDLs) ranged from 4 to 40 ng/L (parts per trillion) with the DAD instrument. PPD detection was highly specific but resulted in a slight loss in chromatographic efficiency and average MDLs approximately 5 times higher using a single set of detection conditions. The study indicates that methods based on SPE followed by HPLC with diode array or PPD detection have practical utility for trace analysis of phenyl ureas in drinking water or surface waters.

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