1,1-Dicyano-4-[4-(diethylamino)phenyl]buta-1,3-dienes: Structure-Property Relationships

We report the synthesis and physical study of a series of 1,1-dicyano-4-[4-(diethylamino)phenyl]buta-1,3-dienes in which the number and position of additional CN substituents along the 1,1-dicyanobuta-1,3-dienyl fragment is systematically varied. While X-ray analysis provided unambiguous information about molecular geometries in the crystal, UV/Vis and electrochemical measurements, by cyclic voltammetry (CV) and rotating disk voltammetry (RDV), revealed that introduction of additional cyano groups in the C2- and C4-positions most affected the optical properties of these molecules in solution, in terms of intramolecular charge-transfer absorption energy and intensity. A comparison with structurally related chromophores indicates that the shift of the anilino donor from position 2/3 to 4 along the butadiene scaffold results in a remarkable bathochromic shift of the ICT absorption maxima, mainly due to the higher planarity in the present series. These findings are further corroborated by density functional theory calculations. Preliminary nonlinear optical (NLO) measurements confirm the promise of the new push-pull chromophores as third-order nonlinear-optical molecular materials.