Validity and possibility of photoconductivity-detected magnetic resonance (PCDMR) method as one of reaction-yield-detected magnetic resonance (RYDMR) methods Takashi Itoh, Akihito Matsuyama, Kiminori Maeda, Hisao Murai * Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan Received 4 July 2000; in ®nal form 14 November 2000 Abstract Fluorescence-detected magnetic resonance and photoconductivity-detected magnetic resonance are simultaneously applied to the system of a radical-ion pair formed in the photoinduced electron transfer reaction between pyrene and 1,3-dicyanobenzene. The former monitors the exciplex ¯uorescence via the singlet radical-ion pair, while the latter monitors free ionic radicals escaping from the radical-ion pair. Both spectra show good coincidence, which shows that the population of the singlet state is proportional to the total radical-ion pair one. The data obtained from the photoconductivity-detected magnetic resonance method suggest the faster quenching reaction of the triplet state of the radical-ion pair than that of the singlet state. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Radical pairs (RPs) are essential transient spe- cies that determine the subsequent reaction path- ways in photochemical systems. Since an RP is born in a pure quantum state and conserves its spin multiplicity, it provides important informa- tion about the reaction dynamics and mechanisms by way of the induction of electron spin polar- ization in free radicals and nuclear spin polariza- tion in products [1,2]. The transient RP is called a spin correlated radical pair (SCRP) which is de- tectable by EPR only when its existence time is long enough. When the RP is under the resonance magnetic ®eld of EPR, the rate of singlet±triplet spin conversion of the RP is in¯uenced by the microwave ®eld, which enables us to detect the EPR spectrum of the RP as the change in the chemical reaction yield. The reaction-yield-detect- ed magnetic resonance (RYDMR) methods are the detection of chemical reactions modulated by electromagnetic radiation in the RP. This method provides the spectrum of the RP and raises new problems about the spin dynamics in the RPs such as the eects of the exchange interaction, dipole± dipole interaction and dynamic motion [3,4]. Several dierent RYDMR methods have been re- ported, ¯uorescence-detected magnetic resonance (FDMR), transient absorption-detected magnetic resonance (ADMR), photoconductivity-detected magnetic resonance (PCDMR), and so on. An FDMR method has been used to obtain information about the spin dynamics of radical- 12 January 2001 Chemical Physics Letters 333 (2001) 242±247 www.elsevier.nl/locate/cplett * Corresponding author. Fax: +81-22-217-6570. E-mail address: murai@orgphys.chem.tohoku.ac.jp (H. Mu- rai). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 0 ) 0 1 3 6 1 - 0