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Three-branched dendritic dipolar nonlinear optical chromophores, more than three times a single-strand chromophore?
Department of Chemie, University of Hamburg.
Department of Chemie, University of Hamburg.
Department of Chemie, University of Hamburg.
Department of Chemie, University of Hamburg.
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2008 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 47, 14751-14761 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2008. Vol. 112, no 47, 14751-14761 p.
Keyword [en]
Dendrimers; Numerical analysis; Ab initio; Computational predictions; Dendritic architectures; Future researches; Hyperpolarizability; Limiting cases; New series; Nlo activities; Nonlinear optical chromophores; Nonlinear optical responses; Nonpolar solutions; Numerical calculations; Semiempirical; Structural changes; Chromophores
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6972DOI: 10.1021/jp802369cISI: 000261056400010Scopus ID: 2-s2.0-57449109538OAI: oai:DiVA.org:kth-6972DiVA: diva2:11837
Note
QC 20100820. Tidigare titel: Three-branched dendritic NLOphores, more than three times a single-strand chromophore? Titel ändrad och uppdaterad från Submitted till Published 20100820.Available from: 2007-04-16 Created: 2007-04-16 Last updated: 2012-03-21Bibliographically approved
In thesis
1. Theoretical Design of Molecular Photonic Materials
Open this publication in new window or tab >>Theoretical Design of Molecular Photonic Materials
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents a theoretical study on optical properties of molecular materials. Special emphasis has been put on the influence of solvent environment, nuclear vibrations, and aggregation effects on molecular properties like linear and nonlinear polarizabilities, one- and two-photon absorption probabilities. All calculations have been performed by means of time independent and dependent quantum chemical methods at the Hartree-Fock and density functional theory levels. Solvation models that include both long range and short range interactions have been employed for calculations of optical properties of molecules in solutions. Pure vibrational and zero-point vibrationally averaged contributions have been taken into account for linear and nonlinear polarizabilities. The linear coupling model is applied to simulate vibronic profiles of optical absorption spectra. The computational strategies described in this thesis are very useful for the design of efficient molecular photonic materials.

More specifically, the nonmonotonic behavior of the solvatochromic shifts and the first hyperpolarizability of para-nitroaniline (pNA) with respect to the polarity of the solvents have been theoretically confirmed for the first time. The significant contributions of the hydrogen bonding on the electronic structures of pNA are revealed. Vibrational contributions to the linear and nonlinear polarizabilities of methanol, ethanol and propanol have been calculated both at the static limit and in dynamic optical processes. The importance of vibrational contributions to certain nonlinear optical processes have been demonstrated. A series of end-capped triply branched dendritic chromophores have been studied with the result that their second order nonlinear optical properties are found strongly dependent on the mutual orientations of the three chromophores, numbers of caps and the conjugation length of the chromophores. Several possible mechanisms for the origin of the Q-band splitting of aluminum phthalocyanine chloride have been examined. Calculated vibronic one-photon absorption profiles of two molecular systems are found to be in very good agreement with the corresponding experiments, allowing to provide proper assignments for different spectral features. Furthermore, effects of vibronic coupling in the nonradiative decay processes have been considered which helps to understand the aggregation enhanced luminescence of silole molecules. The study of molecular aggregation effects on two-photon absorption cross sections of octupolar molecules has highlighted the need to use a hybrid method that combines density functional response theory and molecular dynamics simulations for the design of molecular materials.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 52 p.
Series
Trita-TEC-PHD, ISSN 1653-4468
Keyword
Optical property, Molecular material, Solvent environment, Nuclear vibrations, Aggregation effect
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-4333 (URN)978-91-7178-619-7 (ISBN)
Public defence
2007-04-27, FA32, Roslagstullsbacken 21, AlbaNova University Center, Stockholm, 14:00
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Note
QC 20100820Available from: 2007-04-16 Created: 2007-04-16 Last updated: 2010-08-20Bibliographically approved

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