Spectroscopic Investigation and Theoretical Modeling of Benzothiadiazole-Based Charge-Transfer Chromophores: From Solution to Nanoaggregates

Experimental and theoretical investigations are presented on four quadrupolar molecules constituted of a central electron-acceptor 2,1,3-benzothiadiazole conjugated at both sides with electron-donating thiophene (or 2,2'-bithiophene) substituted groups. Previous investigation of their physicochemical properties demonstrated that thermally induced self-organization might be achieved for one of them. In this study, we further explore the structure-properties relationships for these quadrupolar chromophores also examining their aggregation behavior in organic nanoparticles. Strong spectroscopic evidence of J-aggregates formation is obtained, favored by the presence of branched terminalt alkyl chains. The surprisingly low fluorescence quantum yield of these J-aggregates is rationalized within the essential-state model approach.