Tuning the Behavior of a Hydrotalcite-Supported Sulfonated Bithiophene from Aggregation-Caused Quenching to Efficient Monomer Luminescence

Abstract

The synthesis, electronic spectral, and photophysical properties of a new bithiophene derivative, (2,2′- bithiophene)-3,5,5′-trisulfonic acid, α2-SO3H, were investigated in organic or aqueous solution, in neat oil form, and in the solid state by cointercalation with different amounts of the surfactant 1- heptanesulfonate (HS) into a layered double hydroxide (LDH). In solution the fluorescence quantum yield (ϕF) of α2-SO3H increases by 1 order of magnitude when compared to the unsubstituted bithiophene (α2) counterpart. However, the most dramatic change is obtained when α2-SO3H is incorporated with HS into a Zn,Al-LDH, where values of ϕF up to 58% are obtained in comparison with values of 4% for neat α2-SO3H (as an oil) and 2% for an LDH containing only α2-SO3H. In the solid state (LDH), in addition to the monomeric form of α2-SO3H, H- and other types of aggregates are present, which are found to be dependent on the percentage HS content. Time-resolved fluorescence studies further rationalize this behavior with single and double exponential decays mirroring the contributions of monomers and aggregates. The study validates a strategy of increasing fluorescence in the solid state by introduction of electrodonating groups and isolation of the α2-SO3H units within the LDH structure with an appropriate surfactant (HS).