3 years ago

Impact of position of electron withdrawing cyano groups on nonlinear optical properties of centrosymmetric donor-π-acceptor system

Impact of position of electron withdrawing cyano groups on nonlinear optical properties of centrosymmetric donor-π-acceptor system
Karin Zojer, Jin Sun Park, Ran Hee Kim, Jean-Luc Brédas, Kwang-Sup Lee
Two symmetrically substituted phenylenevinylene D-A-D′-A-D type siblings, (2Z,2′Z)-2,2′-(2,5-dimethoxy-1,4-phenylene)bis(3-(4-(dimethylamino)phenyl)acrylonitrile) (-dscn) and (2Z,2′Z)-3,3′-(2,5-dimethoxy-1,4-phenylene)bis(2-(4-(dimethylamino)phenyl)acrylonitrile) (-dscn), are prepared. We investigate the effect of different but symmetrical location of these cyano groups in vinylene bridges on the 1-photon and 2-photon absorption behaviors. We report that the closeness of CN group on the vinyl group to the central phenyl ring in -dscn induces an intramolecular geometric distortion between the central phenyl ring and vinylene group, preventing the effective π-conjugation length in ground and excited states. Thus, the transition energy that is observed in 1-photon absorption and fluorescence is larger in -dscn than in -dscn. This leads to a different intramolecular charge distribution, as a result of which the linear and nonlinear optical properties strongly depend on the position of acceptors. These results are theoretically unraveled in terms of charge transfer pathways, charge distribution, and charge distribution differences on transition. In the 3-state model, the 2-photon absorption efficiency of the centrosymmetric chromophore is dependent on the effective π-conjugation length in ground and excited states as well as the extent of charge transfer on transitions. The change of position of cyano group on the vinyl group to the central phenyl ring pronouncedly induces an intramolecular geometric distortion differences between the central phenyl ring and vinylene group as well as the transition density on transition.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/qua.25441

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