Structural and solvatochromic studies of a series of tricyanoquinodimethane-based zwitterions

The synthesis and characterization of three new solvatochromic tricyanoquinodimethane zwitterionic systems is reported. (Z)-{beta-[N-(1-Propyl)benzothiazolium-2-yl]-alpha-cyano-4-styryl}dicyanomethanide, C3H7(2)BT3CNQ, (Z)-{beta-[ N-(1-propyl)benzothiazolium-2-yl]-alpha-cyano-4-(2,3,5,6-tetrafluorostyryl)}dicyanomethanide, C3H7(2)BT3CNQF(4), and (Z)-{beta-[N-(1-butyl)benzoselenazolium-2-yl]-alpha-cyano-4-styryl}dicyanomethanide, C4H9(2)BS3CNQ, exhibit negative solvatochromism, consistent with a transition from an ionic ground state to a significantly less polar excited state. X-Ray crystallography measurements confirm the zwitterionic ground state of these novel T3CNQ-based chromophores. The solvatochromic properties of these compounds are compared to those of a series of related quinolinium/pyridinium adducts, and also with those of the Reichardt betaine dye.