Solvent effects and energy transfer processes in luminescent composite

The combination of conjugated polymers and photochromic molecules can result in a composite, which can yield a new photoresponsive material. The efficiency of these materials is due to the process of energy transfer. In this work, the conjugated polymer poly (3-hexylthiophene-co-1,4-phenylene) (PTPh) was synthesized by Suzuki route and the photochromic molecule 4-aminoazobenzene (Azo), synthesized by diazonium salt coupling, were mixed forming a luminescent composite. This new material was obtained in four different solvents, in order to evaluate its influence. When the Azo is added in a solution of PTPh, it was observed a decrease of the emission spectra of the copolymer, indicating the suppression of PTPh due to Foster's energy transfer from PTPh to Azo. The larger energy transfer has been found in ethanol. Density Functional Theory (DFT) calculations have been performed for Azo, an oligomeric model for the PTPh and a complex formed by the Azo and the oligomeric model for PTPh, with two different functionals. Computational results indicate the occurrence of C-H-pi and N-H-S interactions in the optimized structure of PTPh/Azo complex. The LUMO orbital of the PTPh/Azo complex is mainly located in the Azo moiety, suggesting that Azo might receive energy from the polymer. Therefore, the joint computational-experimental study enables the understanding of the energy transfer that takes place in the PTPh/Azo systems.