Effect of metal salts in the optical properties of polydiacetylenes

Films of polydiacetylene (PDA)-containing polyesters with metal salts of Zn, Eu and Gd were prepared. Ultraviolet-visible (UV-VIS) absorption and photoluminescent (PL) spectra indicated that the presence of the metal salts induced a small shift of their maxima to higher and lower energies, respectively. PDAs films with an ester group in allylic position to the conjugated system presented two emission bands. The higher energy emission band was assigned to carbonyl emission and the lower energy emission band to self-trapped excitons (STE). Indeed, the inclusion of metal salts incremented the intensity relation between the higher and lower emission energy bands. On the other hand, Raman spectroscopy measurements performed in PDAs films derived of pentyn-1-ol indicated that the metal salts induced a slight statistical shift in the triple and double bond signals to higher energies. In this way, the intensity variations and band shifts detected by Raman, UV-VIS and PL spectroscopies showed that the presence of metal salts could have a remarkable influence on the energy levels of these PDAs. Nonlinear optical (NLO) third harmonic generation (THG) measurements were performed in order to verify this affirmation as well as the cubic NLO performance of these materials.