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>A timehyphen;resolved EPR study of shorthyphen;lived triplet states: Host and temperature dependences of triplet properties of phthalazine
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A timehyphen;resolved EPR study of shorthyphen;lived triplet states: Host and temperature dependences of triplet properties of phthalazine
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机译：A timehyphen;resolved EPR study of shorthyphen;lived triplet states: Host and temperature dependences of triplet properties of phthalazine
The triplet properties of phthalazine are investigated by means of the timehyphen;resolved EPR technique with laser excitation in various hosts over a wide range of temperature. The host and temperature dependences are interpreted satisfactorily in terms of the vibronic mixing between the3npgr;ast; and3pgr;pgr;ast; states. From the host dependences of the EPR parameters the zfs of the pure3npgr;ast; state of phthalazine is deduced to beXn=0.027 cmminus;1,Yn=minus;0.058 cmminus;1, andZn=0.031 cmminus;1. The fraction of the3npgr;ast; character of theT1state is estimated to be sim;0percnt; in ethanol, benzoic acid (BAC), and 1, 4hyphen;dichlorobenzene (DCB), 14percnt; in 1, 2, 4, 5hyphen;tetrachlorobenzene (TCB), 60percnt; in biphenyl (BP), and 84percnt; in durene. The temperature dependences of the zfs, linewidth, phosphorescence spectrum, and lifetime are investigated and the results are explained using a continuum model. From the simulation of the temperature dependence of the triplet lifetime in the DCB host the decay rate constant of the second excited triplet (3npgr;ast;) state is estimated to be 2.5times;104sminus;1. A drastic increase of the decay rate at higher temperatures suggests the presence of a higher3npgr;ast; state with a decay rate constant of sim;106sminus;1. Possible causes for the lack of phosphorescence and fast radiationless decay are also discussed.
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