title: Temperature dependence of charge separation and recombination in porphyrin oligomer-fullerene donor-acceptor systems.
abstract: Electron-transfer reactions are fundamental to many practical devices, but because of their complexity, it is often very difficult to interpret measurements done on the complete device. Therefore, studies of model systems are crucial. Here the rates of charge separation and recombination in donor-acceptor systems consisting of a series of butadiyne-linked porphyrin oligomers (n = 1-4, 6) appended to C(60) were investigated. At room temperature, excitation of the porphyrin oligomer led to fast (5-25 ps) electron transfer to C(60) followed by slower (200-650 ps) recombination. The temperature dependence of the charge-separation reaction revealed a complex process for the longer oligomers, in which a combination of (i) direct charge separation and (ii) migration of excitation energy along the oligomer followed by charge separation explained the observed fluorescence decay kinetics. The energy migration is controlled by the temperature-dependent conformational dynamics of the longer oligomers and thereby limits the quantum yield for charge separation. Charge recombination was also studied as a function of temperature through measurements of femtosecond transient absorption. The temperature dependence of the electron-transfer reactions could be successfully modeled using the Marcus equation through optimization of the electronic coupling (V) and the reorganization energy (λ). For the charge-separation rate, all of the donor-acceptor systems could be successfully described by a common electronic coupling, supporting a model in which energy migration is followed by charge separation. In this respect, the C(60)-appended porphyrin oligomers are suitable model systems for practical charge-separation devices such as bulk-heterojunction solar cells, where conformational disorder strongly influences the electron-transfer reactions and performance of the device.
authors: Physical Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, Kemivägen 3, 412 96 Göteborg, Sweden.
authors: Axel
authors: A
authors: Kahnt
authors: Joakim
authors: J
authors: Kärnbratt
authors: Louisa J
authors: LJ
authors: Esdaile
authors: Marie
authors: M
authors: Hutin
authors: Katsutoshi
authors: K
authors: Sawada
authors: Harry L
authors: HL
authors: Anderson
authors: Bo
authors: B
authors: Albinsson
references: Annu Rev Cell Biol. 1991;7:1-23
references: 1809346
references: Chemphyschem. 2005 Apr;6(4):732-43
references: 15881590
references: Angew Chem Int Ed Engl. 2006 Dec 4;45(47):7979-82
references: 17083140
references: Photochem Photobiol Sci. 2003 Mar;2(3):251-8
references: 12713225
references: J Phys Chem B. 2005 Jan 20;109(2):716-23
references: 16866432
references: J Phys Chem A. 2008 May 15;112(19):4410-4
references: 18422290
references: ChemSusChem. 2008;1(1-2):97-102
references: 18605671
references: Chem Commun (Camb). 2009 Sep 7;(33):4913-28
references: 19668806
references: Dalton Trans. 2009 May 28;(20):3880-9
references: 19440585
references: Chem Rev. 1998 Nov 5;98(7):2527-2548
references: 11848970
references: Chemistry. 2008;14(12):3765-75
references: 18297668
references: J Am Chem Soc. 2007 Apr 11;129(14):4291-7
references: 17362004
references: Chem Commun (Camb). 2008 Oct 28;(40):4867-74
references: 18931725
references: J Am Chem Soc. 2008 Aug 6;130(31):10171-8
references: 18613666
references: Photochem Photobiol Sci. 2007 Jun;6(6):675-82
references: 17549270
references: J Am Chem Soc. 2005 Jul 13;127(27):9710-20
references: 15998075
references: Phys Chem Chem Phys. 2007 Mar 28;9(12):1400-20
references: 17356749
references: J Phys Chem A. 2008 May 8;112(18):4215-23
references: 18402483
references: Annu Rev Biophys Bioeng. 1973;2:131-56
references: 4583652
references: Chem Commun (Camb). 2010 Oct 14;46(38):7090-108
references: 20835465
references: J Phys Chem B. 2007 Jun 21;111(24):6829-38
references: 17489628
references: J Phys Chem A. 2006 Jan 12;110(1):319-26
references: 16392871
references: Proc Natl Acad Sci U S A. 2003 Feb 4;100(3):946-51
references: 12538865
references: Chem Commun (Camb). 2011 Jan 14;47(2):606-10
references: 20871887
references: Chemistry. 2007;13(26):7385-94
references: 17582819
references: ACS Nano. 2010 Nov 23;4(11):6697-706
references: 21028793
references: Eur J Biochem. 1990 Jan 26;187(2):283-305
references: 2404762
references: J Phys Chem A. 2009 May 21;113(20):5846-54
references: 19402685
references: Chem Soc Rev. 2006 May;35(5):471-87
references: 16636729
references: Angew Chem Int Ed Engl. 2004 Sep 27;43(38):4985-7
references: 15317017