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- Heck, J., et al.
(författare)
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Structure-property relationship in organometallic compounds regarding SHG
- 2007
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Ingår i: Linear and Nonlinear Optics of Organic Materials VII. - : SPIE - International Society for Optical Engineering. - 9780819468017 ; , s. R6530-R6530
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Konferensbidrag (refereegranskat)abstract
- Structure-property relationships based on experimental as well as theoretical results will be elucidated. For this purpose different dipolar organometallic compounds were synthesized and characterized. The alteration of the donor and acceptor termini in mono- and dinuclear sesquifulvalene complexes results in spectroscopic and even structural modifications. The structural and 1H NMR spectroscopic changes correlate with the experimentally obtained first hyperpolarizability. The potent electron-donating (D) group [(CpFeCO)2(μ-CO)(μ-C=CH-)] is combined with different electron-accepting units (A), yielding the push-pull complexes [(CpFeCO) 2(μ-CO)(μ-C=CH-CH=A)]. The extent of electron derealization within the π-bridge connecting the donor D and the acceptor A can be monitored by means of 1H NMR spectroscopy. A correlation between the 3J(Hβ-Hγ) coupling constants and the first hyperpolarizability is found, which very much resembles the dependence of the first hyperpolarizability on the bond length alternation. In order to elucidate the dependence of the NLO response on the conformation of triply branched NLOphores, a new series of dendritic D-π-A structures has been synthesized. A combined approach of experiments and computational predictions was applied both on the dendrimers and on the corresponding single-strand chromophores. These results demonstrate that theoretical calculations are able to reproduce experimental results and show the tendency of the effects due to structural changes.
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- Holtmann, J., et al.
(författare)
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Three-branched dendritic dipolar nonlinear optical chromophores, more than three times a single-strand chromophore?
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:47, s. 14751-14761
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Tidskriftsartikel (refereegranskat)abstract
- To elucidate the dependence of the nonlinear optical (NLO) response on the conformation of triply branched derivatives, a new series of D-pi-A dendrimers has been synthesized. A combined approach of experiments (UV-vis and EOA measurements) and computational predictions (semiempirical and ab initio) was applied both on the dendrimers and on the corresponding single-strand chromophores. It has been shown that depending on the surrounding media the NLO activity of a flexible dendrimer can be very different. Two limiting cases are proposed: (i) the dendrimer resembles a solution of the corresponding single-strand chromophores with about 3-fold concentration, where the hyperpolarizability is the sum of the effect of three noninteracting single-strand subunits ("independent chromophores" limit); (ii) the dendrimers show nearly parallel or helical alignments of the single-strand subunits. Because of this change of conformation the NLO activity can be enhanced up to nine times the value of the "independent chromophores" limit and, thus, are more than a single strand chromophore. Conformers of dendrimers with interacting single-strand chromophores have been identified experimentally in nonpolar solutions by the EOA spectroscopy and possible structures have been revealed by numerical calculations, which could moreover show the tendency of the effects on the hyperpolarizability due to structural changes of the flexible dendritic architecture. Implications for future research developments are given to implement the "more than three times" concept.
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