Rigid-Rod Sensitizers bound to Semiconductor Nanoparticles
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1031-H09-50
Rigid-Rod Sensitizers bound to Semiconductor Nanoparticles Olena Taratula, and Elena Galoppini Chemistry Department, Rutgers University, 73 Warren Street, Newark, NJ, 07102 ABSTRACT A series of “rigid-rod” dyes with an organic chromophore (pyrene or coumarin) attached through an oligophenylenethynylene (OPE) rigid bridge, linear or branched, to an anchoring isopthalic acid unit (Ipa) were synthesized and studied for solar cells (DSSCs) applications. The new dyes were attached to metal oxide (MOn = TiO2, ZrO2 and ZnO) nanoparticles films via the two COOH binding groups on the Ipa unit to investigate their binding and photophysical properties at the semiconductor surface. FTIR-ATR spectra show that all dyes did bind to the metal oxide films through carboxylate bonds. Fluorescence emission on insulating ZrO2 films was employed to study aggregation of the organic rigid-rods. Studies of the pyrene rigid-rods in solar cells showed near quantitative conversation of absorbed photons into electricity. INTRODUCTION In DSSCs, a dye molecule is covalently attached to a nanostructured semiconductor oxide film. Upon light absorption, an electron is transferred from the excited dye to the semiconductor. Then the electron diffuses through the semiconductor nanoparticles to the electrode and the photoelectrochemical cycle is completed by electron donation to the oxidized dye (regeneration) by a redox system in the electrolyte [1]. The molecular design of novel photosensitizing chromophores is an important area of DSSCs research. N O
organic chromophore
O
OPE bridge
HOOC
COOH
n
Ipa anchoring unit
"rigid-rod" dyes
COOH
HOOC
1 (n = 0) 2 (n = 1)
n
HOOC
COOH
HOOC
COOH
4
3 N
HOOC
COOH
5 (n = 0) 6 (n = 1) 7 (n = 2)
O O COOH
py-1-COOH
COOH
coumarin 343
Figure 1. Organic rigid-rods with pyrene (1-4) and coumarin (5-7) described in this study, and references compounds.
Lately, organic sensitizers anchored through rigid linkers have been developed to study the interfacial electron injection [2]. Such models are used to control the distance between the chromophore and the semiconductor surface and tune the photophysical properties of the dyes, for instance, increasing extinction coefficients by extending the conjugation. In this paper we describe our recent studies of a series of organic rigid-rods (Figure 1). The properties of novel compounds 5-7 were compared to the pyrene series (1-4) that we had previously described [3, 4]. In particular, the influence of OPE bridge length and branching on photophysical and binding properties of rigid-rods was investigated. EXPERIMENT Pyrene-1-carboxylic acid, coumarin 343 and deoxycholic acid (DCA) were purchased from Aldrich. The synthesis of 1-4 [3, 4] and 5-7 [5] has been described. TiO2, ZrO2 and ZnO colloidal nanoparticle thin films were prepared by well-known sol-gel techniques [6, 7]. For binding studies, the colloidal films were cast onto cover glass slides, and fluorine-doped tin oxide (FTO) glass (7 Ω for sq.cm, Pilkington) was used for photoelectrochemica
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