Electronic Structure of Bis(4‐dimethylaminophenyl)squaraine

Abstract

AbstractThe structural and electronic features of bis(4‐dimethylaminophenyl)squaraine (1) has been studied using density functional BLYP/ cc‐pVTZ level of theory. The quinoid character of 1 is correlated to the partial double bond character of C‐NMe2 (1.379 Å) and C−O (1.236 Å) bonds which leads to accumulation of positive charge on NMe2 groups and negative charge on carbonyl oxygen. Further, the diagonal C1 C3 (2.086 Å) and C2 C4 (2.116 Å) distances of the squaric ring indicated a 1,3 type C−C orbital interaction. Molecular electrostatic potential (MESP) topographical analysis confirmed the charge separated quadrupolar nature of 1. The MESP minimum, Vmin located at the carbonyl oxygen, −62.5 kcal/mol, confirmed its highly electron rich character arising from the quinoid structure. The electronic structure of 1 revealed from MESP confirmed its quadrupolar nature and suggested the location of positive charge on NMe2 groups. The typically used chemical structure drawing of 1 showing +2 charge on the squaraine ring is inaccurate and misleading. The solvatochromic behaviour of 1 can be attributed to its quadrupolar electronic structure wherein the electron rich carbonyl groups provide room for noncovalent interactions with multiple solvent molecules.