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ABSTRACT: Synthetic strategies and basic molecular principles were investigated in order to achieve chromophores absorbing light in the far red or even near infrared region. Therefore, a comprehensive series of new squaraine dyes were synthesized and characterized. Beside monomeric unsymmetrical and symmetrical squaraine dyes, also squaraine dye dimers and oligomers bridged with phenylene, fluorene, iso-octyloxy phenylene and tetrafluoro phenylene moieties or directly coupled via condensation reaction were obtained. The influence of the various molecular dye structures to their absorption properties was studied with UV-vis measurements supported by theoretical investigations applying Kiprianov’s theory of coupled dyes. With regard to Meyer’s theory of the limiting values, the effective number of repeating units for dye series for the highest possible absorption maximum was determined. Observed trends and limiting values for electrochemical potentials and electrical band gaps of the dyes are in agreement with the UV-vis investigations. Finally, calculated molecular structures and frontier orbitals of dimers verify the results of the optophysical and electrochemical studies.
Dyes and Pigments 01/2012; · 3.13 Impact Factor
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ABSTRACT: An optimized unsymmetrical squaraine dye 5-carboxy-2-[[3-[(2,3-dihydro-1, 1-dimethyl-3-ethyl-1H-benzo[e]indol-2-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-3,3-dimethyl-1-octyl-3H-indolium (SQ02) with carboxylic acid as anchoring group is synthesized for dye-sensitized solar cells (DSCs). Although the pi-framework of SQ02 is insignificantly extended compared to its antecessor squaraine dye SQ01, photophysical measurements show that the new sensitizer has a much higher overall conversion efficiency eta of 5.40% which is improved by 20% when compared to SQ01. UV-vis spectroscopy, cyclic voltammetry and time dependent density functional theory calculations are accomplished to rationalize the higher conversion efficiency of SQ02. A smaller optical band gap including a higher molar absorption coefficient leads to improved light harvesting of the solar cell and a broadened photocurrent spectrum. Furthermore, all excited state orbitals relevant for the pi-pi* transition in SQ02 are delocalized over the carboxylic acid anchoring group, ensuring a strong electronic coupling to the conduction band of TiO2 and hence a fast electron transfer.
Advanced Functional Materials 01/2009; 19:2720-2727. · 10.18 Impact Factor
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William Kylberg,
Ying Zhang,
Arthur Aebersold,
Fernando Araujo Castro,
Thomas Geiger,
Jakob Heier, Simon Kuster,
Chang-Qi Ma,
Peter Bäuerle,
Frank Nüesch,
Jean-Nicolas Tisserant,
Roland Hany
Organic Electronics 13(7):1204 - 1212. · 4.05 Impact Factor
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ABSTRACT: A fully conjugated unsymmetrical dimeric squaraine dye was synthesized. The synthetic key step for this dye, a selective Knoevenagel type condensation of end groups to the core moiety, allows the incorporation of a carboxylic acid function essentially for the strong coupling to the titanium dioxide (TiO2) surface. Moreover, the dimer exhibit outstanding optical properties such as absorption maximum in the NIR region with a huge molar absorption coefficient. The solvatochromic effects were also studied. Furthermore the electrochemical properties were determined with cyclic voltammetry. The reduction potential is just high enough to allow an efficient photo induced charge injection into the conduction band of the TiO2 semiconductor and the oxidation potential lies about 300 mV below the potential of the iodide / triiodide redox couple providing a good regeneration driving force. From electron density distribution calculations of the optimized BSQ01 structure we could see the directional charge displacement from the solvent exposed side in the HOMO to the carboxyl anchor group in the LUMO. The dimer was immobilised on TiO2 nanoparticles and a first dye sensitized solar cell was made as a proof-of-concept. (C) 2010 Elsevier Ltd. All rights reserved.
