Chemically and Photochemically Stable Conjugated Poly(oxadiazole) Derivatives:  A Comparison with Polythiophenes and Poly(p-phenyleneethynylenes)

We have designed and synthesized highly stable conjugated poly(oxadiazoles) derivatives (PO1 and PO2). The oxadiazole-containing conjugated polymers have a strong photoluminescent property and are completely soluble in organic solvents. PO1 and two commonly used conjugated polymers, PPE and P3HT, were tested under strong acidic condition and strong UV irradiation condition to investigate their chemical and photochemical stability. PO1 turned out to be intact through the harsh treatments while the two control polymers were severely damaged in their conjugated backbone and lost their emissive property. Protonation of the oxadiazole unit of PO1 by acids induced backbone planarization of PO1, resulting in emission color change from blue to green. Reversible color change by adding and removing trifluoroacetic acid (TFA) to PO1 and latent fluorescent patterning by using a photoacid generator and UV irradiation through a photomask were demonstrated. The results provide a design principle to develop highly stable conjugated polymers for various applications where photobleaching and oxidation are a common challenging problem.