TY - JOUR
T1 - On the g-value shift and intersystem crossing in photo-excited radical-triplet systems
AU - Iwasaki, Y.
AU - Katano, K.
AU - Ohba, Y.
AU - Karasawa, Satoru
AU - Koga, N.
AU - Yamauchi, Seigo
PY - 2003/1/1
Y1 - 2003/1/1
N2 - The electron paramagnetic resonance (EPR) signals of photoexcited quartet (Q1) states for zinc(II) tetra-tert-butyl-phthalocyanine (ZnPc) ligated by 3- and 4-(N-nitronyl-nitroxide) pyridine radicals (3-NOPy, 4-NOPy) were observed in toluene solution at room temperature by means of X-band (9.4 GHz) time-resolved EPR (TREPR) spectroscopy. The g values of Q1 in the ZnPc-3-NOPy and ZnPc-4-NOPy complexes were found to be g = 2.0025 and g = 2.0036, respectively. The obtained g value (2.0036) for ZnPc-4-NOPy is in good agreement with the value (g = 2.0037) of the Q1 state calculated under the strong-exchange limit. The g value (2.0025) is just an average of the Q1 and D1 (g = 2.0013) states for ZnPc-3-NOPy. The g value of Q1 for zinc(II) meso-tetraphenylporphine (ZnTPP) ligated by 3-NOPy showed a slight shift (g = 2.0027) at X-band and no shift (g = 2.0031) at W-band from the calculated g value (g = 2.0031) (J. Fujisawa, Y. Iwasaki, Y. Ohba, S. Yamauchi, K. Koga, S. Karasawa, M. Fuhs, K. Möbius, S. Weber, Appl. Magn. Reson. 21, 483-493, 2001). These changes in the g value were found to originate from an averaging of the TREPR spectra over the Q1 and photoexcited doublet (D1) states via a fast intersystem crossing (ISC) process. The ISC rates between these two states were estimated by means of numerical calculations with the modified Bloch equations as 1.2 · 108 and 6 · 107 s-1 for the ZnTPP-3-NOPy complex at the X- and W-bands, respectively. The lower limit of the ISC rate was obtained as 109 s-1 for the ZnPc-3-NOPy complex and the higher limit was found to be 3.1 · 108 s-1 for the ZnPc-4-NOPy complex.
AB - The electron paramagnetic resonance (EPR) signals of photoexcited quartet (Q1) states for zinc(II) tetra-tert-butyl-phthalocyanine (ZnPc) ligated by 3- and 4-(N-nitronyl-nitroxide) pyridine radicals (3-NOPy, 4-NOPy) were observed in toluene solution at room temperature by means of X-band (9.4 GHz) time-resolved EPR (TREPR) spectroscopy. The g values of Q1 in the ZnPc-3-NOPy and ZnPc-4-NOPy complexes were found to be g = 2.0025 and g = 2.0036, respectively. The obtained g value (2.0036) for ZnPc-4-NOPy is in good agreement with the value (g = 2.0037) of the Q1 state calculated under the strong-exchange limit. The g value (2.0025) is just an average of the Q1 and D1 (g = 2.0013) states for ZnPc-3-NOPy. The g value of Q1 for zinc(II) meso-tetraphenylporphine (ZnTPP) ligated by 3-NOPy showed a slight shift (g = 2.0027) at X-band and no shift (g = 2.0031) at W-band from the calculated g value (g = 2.0031) (J. Fujisawa, Y. Iwasaki, Y. Ohba, S. Yamauchi, K. Koga, S. Karasawa, M. Fuhs, K. Möbius, S. Weber, Appl. Magn. Reson. 21, 483-493, 2001). These changes in the g value were found to originate from an averaging of the TREPR spectra over the Q1 and photoexcited doublet (D1) states via a fast intersystem crossing (ISC) process. The ISC rates between these two states were estimated by means of numerical calculations with the modified Bloch equations as 1.2 · 108 and 6 · 107 s-1 for the ZnTPP-3-NOPy complex at the X- and W-bands, respectively. The lower limit of the ISC rate was obtained as 109 s-1 for the ZnPc-3-NOPy complex and the higher limit was found to be 3.1 · 108 s-1 for the ZnPc-4-NOPy complex.
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U2 - 10.1007/BF03166628
DO - 10.1007/BF03166628
M3 - Article
AN - SCOPUS:0037262599
VL - 23
SP - 377
EP - 391
JO - Applied Magnetic Resonance
JF - Applied Magnetic Resonance
SN - 0937-9347
IS - 3-4
ER -