1381967-98-1Relevant articles and documents
Exciton coupling effects in polymeric cis-indolenine squaraine dyes
Voelker, Sebastian F.,Lambert, Christoph
experimental part, p. 2541 - 2553 (2012/09/07)
Dicyanovinylene-substituted cis-indolenine squaraines were polymerized by a Ni-mediated Yamamoto homocoupling reaction. Preparative recycling GPC was used to obtain polymer fractions with different molecular weight distributions in order to investigate the influence of molecular weight on the optical properties. In this attempt, conjugated cyclic trimers could also be isolated that are, to the best of our knowledge, the first of their kind. These trimers and the squaraine polymers were investigated by cyclic voltammetry, absorption spectroscopy, and static and time-resolved fluorescence spectroscopy. While the trimers show multiple fluorescence bands with, for squaraines, an exceptional huge Stokes' shift, the polymers show broad absorption in the red to near infrared (NIR) region with narrow fluorescence and only the common minor Stokes' shift. The spectral features of the squaraines were interpreted to be caused by excitonic coupling. By comparison of experimental and computed (CNDO/S2 CIS) spectra detailed, structural models of the polymers were derived that consist of helix (H-aggregate behavior) and zigzag motifs (J-aggregate behavior).
