A Layered Red-Emitting Chromophoric Organic Salt

We have investigated a synthetic route as well as the molecular assembly and the optical properties of a novel π-conjugated system, namely, the anion (E)-3-(3-amino-2,4-dicyanophenyl)-1,1-dicyanoprop-2-en-1-ide, in the form of its tetrabutylammonium salt (1). Through the combined actions of directional hydrogen bonds and Coulombic interactions, a two-dimensional molecular topology is realized whereby the extended monolayers of the strongly chromophoric π-conjugated anions are spatially isolated by the tetrabutylammonium cations. The chromophoric properties of the anion originate from very intense low-energy π−π* absorptions, with a high oscillator strength, fexp = 0.84 at 468 nm. Further characteristic features are a S1 → S0 fluorescence emission not only in solution but also in the solid state at room temperature. The remarkable type of organization of the organic chromophores into a solid state sheet structure suppresses a possible quenching of a solid state emission and, quite interestingly, allows in principle probing of the photoexcited exciton states based on a defined molecular geometry.