Effect of electron withdrawing groups on near infrared absorption of quinaldine-based squaraine dyes

摘要

The quinaldinium salt possessing electron withdrawing (-COOEt) groups was condensed with squaric acid giving the quinaldine based symmetrical squaraine dye. Effect of electron withdrawing group on near infrared absorption of the squaraine dye has been studied. Results showed that electron withdrawing group shifts bathochromically the absorption wavelength of squaraine dye by 31 nm when compared with the unsubstituted dye. Computational studies were performed in order to understand the charge transfer and red shift and later have been attributed to the increased biradicaloid character.