Push-pull olefinic           chromophores are systems characterized by  an         electron-withdrawing and an         electron-donating group  substituting each side of the double         bond. As a          consequence, the double bond is very polarized and the          rotational barrier is         lower than that of an ordinary olefin.  Such properies make         push-pull olefins interesting          candidates for molecular switches. In this work we investigate          push-pull quinodimethanes, which additionally have awakened considerable          interest as         candidates for second order NLO (non-linear  optics) materials.         Highly accurate         multiconfigurational  ab initio calculations show that no S0/S1 conical intersection exist for the cis-trans isomerization         in these         cases, only different S1/S2 degeneracies  at         twisted geometries around any of the two double bonds.  Quantum         wavepacket         propagations in reduced  dimensionality, comprising exclusively         the two         torsional  degrees of freedom, are employed to         investigate the          deactivation pathways through the conical intersections allowing for  interferences effects.         Additionally, ab         initio  surface-hoping molecular dynamics is used to inspect         which  additional         degrees of freedom are necessary to describe the  non-adiabatic         dynamics of         push-pull quinodimethanes more  realistically.

Conical intersections and         non-adiabatic dynamics in         push-pull quinodimethanes

244th National Meeting (2012)

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