Electronic communication in tetrathiafulvalene (TTF)/C60 systems: toward molecular solar energy conversion materials?
ABSTRACT The covalent connection of the electron acceptor C 60 to p-quinonoid pi-extended tetrathiafulvalenes (exTTFs) has allowed for the preparation of new photo- and electroactive conjugates able to act as artificial photosynthetic systems and active molecular materials in organic photovoltaics. The gain of aromaticity undergone by the pi-extended TTF unit in the oxidation process results in highly stabilized radical ion pairs, namely, C 60 (*-)/exTTF (*+). Lifetimes for such charge-separated states, ranging from a few nanoseconds to hundreds of microseconds, have been achieved by rationally modifying the nature of the chemical spacers. These long-lived radical pairs are called to play an important role for the conversion of sunlight into chemical or electrical power.
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ABSTRACT: A series of triphenylamine-based aromatic cyano compounds have been synthesized as red-emitting fluorophores with large Stokes shifts in both solution (>100 nm in CHCl3) and solid state (>150 nm in film). Intramolecular charge transfer (ICT) properties of the synthesized compounds are examined using UV–Vis absorptions, photoluminescence measurements and solvatochromic studies. Our studies suggest that Stokes shifts of these compounds can be fine-tuned by manipulating the ICT strength between donor and acceptor with various electronic donating groups, and the largest Stokes shifts are typically associated with compounds that have the strong ICT characters. The observed spectroscopic properties of the compounds are consistent with theoretical calculations using density function theory (DFT) or time-dependent density function theory (TD-DFT). The calculations suggest that the ICT occurs from localized HOMO to localized LUMO with magnitudes of 60–80%. The relative quantum yields of these fluorophores in solution are various and highly solvent dependent. In solid state, the quantum yields of the compounds are significantly increased and some can reach to 0.40.Journal of Photochemistry and Photobiology A Chemistry 01/2013; 251:1–9. DOI:10.1016/j.jphotochem.2012.10.002 · 2.29 Impact Factor
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ABSTRACT: The synthesized benzothiadiazole-based series fluorophores as potential wavelength-shifting materials exhibit large Stokes shifts (>160 nm) with multiple broad absorbance bands from UV region to 600 nm and a strong fluorescence peak around 700 nm (in CHCl3). Intramolecular charge transfer (ICT) characters of the synthesized compounds are examined using UV–vis and photoluminescence solvatochromic shift measurements. Among the synthesized compounds, the fluorophores with asymmetrical structures exhibit larger Stokes shifts than those with symmetrical structures due to large dipole moment changes upon excitation. The fluorophores with electron-donating methoxyl groups attached to the triphenylamine donors are found to have strong ICT properties. Photophysical experimental results are supported by theoretical calculations using Density Function Theory (DFT) and Time Dependent Density Function Theory (TD-DFT) methods. Calculated frontier molecular orbitals (MOs) of ground states on these fluorophores showed an increase in ICT character up to 50% from HOMO to LUMO. Geometric optimization calculations of the excited state reveal that these fluorophores show a more planar structure for the excited state than the ground state, which allows more π–π* overlap and leads to larger Stokes shifts and higher quantum yields.Journal of Photochemistry and Photobiology A Chemistry 03/2012; 231(1):51–59. DOI:10.1016/j.jphotochem.2012.01.011 · 2.29 Impact Factor
Article: TTF-modified DNAChemistry 02/2008; 14(19):5732-6. DOI:10.1002/chem.200800505 · 5.70 Impact Factor