Synthesis, Photo- and Electro- Optical Properties of Luminescent Pi-conjugated Polymers

摘要

The focus of this work is the synthesis, structure, and luminescent properties of n-conjugated polymers. The polymer properties may be tailored with various functional groups, resulting in an increase of emission efficiency and colour tunability. These polymers are important since polymer light emitting diodes (PLEDs) may be used in the production of next generation displays. For this reason, it is important understand the structure-property relationships of luminescent n-conjugated polymers, and their spatial controlled deposition. Three classes of luminescent n-conjugated polymers are investigated herein - poly(3-alkylthiophene)~ (P~ATs), poly(phenyleneviny1ene) (PPVs), and poly(fluorene-co-thiophene) (PFTs). Their structure-property relationships were studied by post-functionalization and host-guest type methodologies. Post-functionalization - via electrophilic aromatic substitution - of P3AT and PPV was efficient, and provided a precise method to control the effective conjugation length. Further post-functionalization of the P3AT system via Pdcatalyzed cross coupling proved effective for obtaining a plethora of 3,4- disubstituted P3ATs. It was found that sterically encumbered groups increased the luminescence efficiency by increasing the interlayer distance between the polymer chains. Alternating poly(fluorene-co-thiophene)~ were prepared with 2,5-, 2,4- and 3,4-thiophene linkages. The type of thiophene linkage had a dramatic effect on the emission colour - from UV emitting to green - while little effect was observed for the emission efficiency. Since the strong spectral overlap between the emission of the 3,4-linked PFT with the absorption of 2,5-linked PFT, and the molecular similarity, host-guest systems via blending and copolymerization was investigated. In an effort to obtain high energy emission, a PFT with 2,7-linked fluorene as the guest in a 3,4-linked PFT host were also investigated. Tetrahydropyan (THP) bearing conjugated polymers have proven useful for obtaining spatial controlled deposition. Since these polymers are important for high resolution displays, the photo-physics of these polymers were investigated. Two classes of THP-containing conjugated polymers were studied; namely, P3ATs and PFTs. For P3ATs, it was found that shorter alkyl chain spacers enhanced the emission efficiency and tuned the emission colour. Upon thermolytic cleavage of the THP group, the luminescence efficiency decreased dramatically. Since PFTs are inherently more luminescent than P3ATs, PFTs bearing THP-groups were also investigated.