Structure−Property Relationships in Push−Pull Amino/Cyanovinyl End-Capped Oligothiophenes:  Quantum Chemical and Experimental Studies

A series of push−pull chromophores built around thiophene-based π-conjugating spacers and bearing various types of amino donors and cyanovinyl acceptors have been analyzed by means of UV−vis−NIR, IR, and Raman spectroscopic measurements in the solid state as well as in solution. The intramolecular charge transfer (ICT) of these π-conjugated systems has also been tested by analyzing the ability of the solute molecules to undergo shifts in their fluorescence emission maxima with increasing solvent polarity. These push−pull oligomers also display an attractive electrochemical behavior since they generate stable species both upon oxidation and reduction. Oxidation mainly involves changes in the electron-rich aminooligothienyl half-part of the molecule and leads to the formation of stable cations. On the other hand, reduction to radical anions and dianions is mainly cyanovinyl-centered but also affects the π-conjugated electron relay. Density functional theory (DFT) calculations have been carried out to help the assignment of the most relevant electronic and vibrational features and to derive useful information about the molecular structure of these NLO-phores.