Electronic Structure of Bis(4-dimethylaminophenyl)squaraine

摘要

The 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 A)and C-O(1.236 A)bonds which leads to accumulation of positive charge on NMe2 groups and negative charge on carbonyl oxygen.Further,the diagonal C1 C3(2.086 A)and C2 C4(2.116 A)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,V_(min)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.