OBSERVATION OF BROAD EPR-SPECTRA OF TRANSIENT FREE-RADICALS BY FT-EPR

Application of electron spin echo Fourier transform EPR (ESE-FT-EPR) t o photo-induced chemical reactions is presented. Main purpose of this study is to observe broad EPR spectra of free radicals having very sho rt T2 by means of the ESE-FT-EPR technique. Details of the experiment al procedures are described. In ESE experiments design of the resonato r is important to obtain sufficient spectral bandwidth because of use of multiple pulses which decreases the bandwidth. We designed and cons tructed Loop-Gap-Resonators (LGR) for light irradiation experiments an d their specifications were examined. The phase cycling method is esse ntial to obtain pure ESE signals and proper time resolution by elimina ting-unwanted FID signals which result from imperfect pulse angles. We applied this technique to observe the photo-induced electron transfer reaction between tetraphenylporphinato zinc(II) (ZnTPP) and duroquino ne (DQ) in an ethanol solution, and successfully observed the time res olved EPR spectra of the both Zn(TPP) cation and DQ anion radicals by ESE-FT-EPR of the Hahn echo. The half-height full-width of envelope of EPR spectrum of Zn(TPP)+, which is never observed in ordinary FT-EPR, is about 16 MHz. Specificity of spectra and the time resolution are c ompared among the ESE-FT-, FT- and cw-Time-Resolved-EPR (cw-TREPR) tec hniques.