Solvent effects on the intrinsic enhancement factors of the triplet exciplex generated by photoinduced electron transfer reaction between eosin Y and duroquinone

Abstract

The spin dynamics of the duroquinone anion radical (DQ · ¡ ) generated by photoinduced electron transfer reactions from triplet eosin Y ( 3 EY 2¡ ) to DQ have been studied by using transient absorption and pulsed EPR spectroscopy. Unusual net-absorptive electron spin polarization plus net-emissive polarization were observed, suggesting the production of the triplet exciplex or contact radical pair as the reaction intermediate. The kinetic parameters and intrinsic enhancement factors of the electron spin polarization were determined in various alcoholic solvents. The net-absorptive electron spin polarization was also observed in ethanol± water mixed solvents. The solvent e ects on the radical yield are analysed on the basis of a stochastic Liouville equation established for the magnetic ®eld e ects on the radical yield. The zero-®eld splitting constants of the triplet exciplex are estimated from the solvent viscosity dependence of the enhancement factors due to spin±orbit coupling induced depopulation of the reaction intermediate.

Spin dynamics and zero-field splitting constants of the triplet exciplex generated by photoinduced electron transfer reaction between erythrosin B and duroquinone

“…The assignment of EB ÅÀ and DQ ÅÀ is confirmed by the quenching reaction of EB ÅÀ by triethanolamine (TEOA) [22,24] [25]. The / esc value of 0.40 determined in the present system is smaller than the value (0.54) in the EY 2À -DQ system [22].…”

“…The / esc value of 0.40 determined in the present system is smaller than the value (0.54) in the EY 2À -DQ system [22]. A similar spectral change was also observed in MeOH, 1-PrOH and 1-BuOH but significant solvent effects on / esc were obtained.…”

“…Nanosecond transient absorption spectra were measured by using a multichannel analyzer (Diode array: Princeton Instruments, IRY-700) controlled with a personal computer as described previously [22]. A Holographic Notch-plus TM filter (Kaiser Optical System, HNPF-532) was used to protect the detector from the strong laser light.…”

“…The kinetic parameters and intrinsic enhancement factors obtained by FT-EPR spectroscopy are summarized in Table 1 Tables 1 and 2 against solvent viscosity (g). The data for the EY 2À -DQ system [22] are also shown for comparison.…”

“…The unusual net-A polarization is attributable to sublevel selective intersystem crossing (ISC) from the triplet exciplex or contact radical pair to the singlet ground state. Furthermore, in a recent Letter, we reported that the radical yield and intrinsic enhancement factor of the electron spin polarization for the eosin Y (EY 2À )-duroquinone (DQ) system depend on the solvent viscosity (g) [22]. The ZFS parameters of the triplet exciplex intermediate were determined from the correlation between the enhancement factors of the electron spin polarization and g.…”