Switching of emissive and NLO properties in push-pull chromophores with crescent PPV-like structuresElectronic supplementary information (ESI) available: Additional graphs and tables, copies of NMR spectra of newly synthesized compounds. CCDC 893805. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2cp43140h

• Main Authors: Coluccini, Carmine, Sharma, Arvind K, Caricato, Marco, Sironi, Angelo, Cariati, Elena, Righetto, Stefania, Tordin, Elisa, Botta, Chiara, Forni, Alessandra, Pasini, Dario
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp43140h

We report on a series of novel homologous push-pull compounds, in which identical donor (a dimethylamino) and acceptor (a malonate ester) functionalities endcap crescent PPV fragments, bearing, respectively, 1, 2 and 3 p -phenylenevinylene units in direct linear conjugation (compounds 7-9 ). The three compounds exhibit striking differences in their linear and nonlinear optical properties. The shorter compound 7 exhibits aggregation-induced emission with a strong luminescence in the solid state (blue emission, photoluminescence quantum yield 38%), and it is nonemissive in solution; the more extended conjugated systems 8 and 9 show classical aggregation-caused quenching in the solid state, while high quantum yield photoluminescence (21 and 93% in toluene) is restored in diluted solutions, through mechanisms involving intramolecular charge transfer in the excited states. EFISH measurements in solutions demonstrate a strong solvent and concentration dependence. As rationalized with the aid of molecular modelling, compounds 8 and, more markedly, 9 aggregate in stable centrosymmetric dimers in solution. Crescent PPV-like "push-pull" organic chromophores exhibit intriguing linear and nonlinear optical properties.