Role of the Spacer in the Singlet-Singlet Energy Transfer Mechanism (Förster vs Dexter) in Cofacial Bisporphyrins

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• 作者：S&eacute ; bastien Faure ; Christine Stern ; Roger Guilard ; and Pierre D. Harvey
• 刊名：Journal of the American Chemical Society
• 出版年：2004
• 出版时间：February 4, 2004
• 年：2004
• 卷：126
• 期：4
• 页码：1253 - 1261
• 全文大小：244K
• 年卷期：v.126,no.4(February 4, 2004)
• ISSN：1520-5126

文摘

The cofacial bisporphyrins H₄DPS (DPS = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene), H₄DPO (DPO = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzofuran), H₄DPX (DPX = 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene), H₄DPA (DPA = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]anthracene), and H₄DPB (DPB = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene) have been monometalated by Zn(OAc)₂·2H₂O and by GaCl₃ to explore the singlet-singlet energytransfer from the photoexcited metal porphyrin center to the linked free base porphyrin. The spectroscopic(UV-vis and fluorescence) and photophysical properties (fluorescence lifetimes, mages/gifchars/tau.gif" BORDER=0 >_F, and quantum yields,mages/gifchars/Phi.gif" BORDER=0 >_F) have been investigated at 298 and 77 K in degassed 2-MeTHF for the donor-acceptor systems, (Zn)H₂DPS, (Zn)H₂DPO, (Zn)H₂DPA, (Zn)H₂DPX, and (Zn)H₂DPB, as well as for the bis-zinc complexes,(Zn)₂DPS, (Zn)₂DPO, (Zn)₂DPX, and (Zn)₂DPB, respectively, and the monoporphyrin derivatives, H₂P, (Zn)P,and (Ga-OMe)P (P^2- = 5-phenyl-2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrin-dianion). The singlet-singlet energy transfer rate constants (K_ET) were obtained using K_ET = (1/mages/gifchars/tau.gif" BORDER=0 >_F -1/mages/gifchars/tau.gif" BORDER=0 >_Fmages/entities/deg.gif">), where mages/gifchars/tau.gif" BORDER=0 >_Fmages/entities/deg.gif"> is thefluorescence lifetime of the corresponding bis-zinc(II) systems (or (Zn)P and (Ga-OMe)P) where no energytransfer occurs. The mages/gifchars/tau.gif" BORDER=0 >_F value for three bis-zinc(II) compounds varies from 1.69 to 2.01 ns and is 1.84 (at298 K) and 3.20 ns (at 77 K) for (Ga-OMe)P. In the donor-acceptor bismacrocycles, depending on thespacer and the temperature, the fluorescence lifetimes decrease down to 50-240 ps. The K_ET valuesrange from ~4 to ~21 (ns^-1) and have been analyzed considering both the Förster and the Dextermechanisms. Using the C_meso-C_meso distance parameters in the calculations, the Förster and Dextermechanisms operate for DPS and DPO, and for DPA, DPX, and DPB spacer systems, respectively. Thelimit distance where one mechanism dominates over the other is estimated to be around 5-6 Å.