Effective Shielding of Triplet Energy Transfer to Conjugated Polymer by Its Dense Side Chains from Phosphor Dopant for Highly Efficient Electrophosphorescence

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• 作者：Szu-Po Huang ; Tzu-Hao Jen ; Yen-Chun Chen ; An-En Hsiao ; Shu-Hui Yin ; Hsiang-Yun Chen ; Show-An Chen
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：April 9, 2008
• 年：2008
• 卷：130
• 期：14
• 页码：4699 - 4707
• 全文大小：585K
• 年卷期：v.130,no.14(April 9, 2008)
• ISSN：1520-5126

文摘

To examine the quenching of a triplet exciton by low triplet energy (E_T) polymer hosts with differentchain configurations for high E_T phosphor guests, the quenching rate constant measurements were carriedout and analyzed by the standard Stern-Volmer equation. We found that an effective shielding of tripletenergy transfer from a high E_T phosphor guest to a low E_T polymer host is possible upon introducing denseside chains to the polymer to block direct contact from the guest such that the possibility of Dexter energytransfer between them is reduced to a minimum. Together with energy level matching to allow chargetrapping on the guest, high device efficiency can be achieved. The extent of shielding for the systems ofphenylene-based conjugated structures from iridium complexes follows the sequence di-substituted (octoxylchain) in the para position (dC₈OPPP) is greater than monosubstituted (mC₈OPPP) and the PPPs withlonger side chains are much higher than a phenylene tetramer (P4) with two short methyl groups. Further,capping the dialkoxyl-susbstituents with a carbazole (Cz) moiety (CzPPP) provides enhanced extent ofshielding. Excellent device efficiency of 30 cd/A (8.25%) for a green electrophosphorescent device can beachieved with CzPPP as a host, which is higher than that of dC₈OPPP as host (15 cd/A). The efficiencyis higher than those of high E_T conjugated polymers, poly(3,6-carbazole) derivatives, as hosts (23 cd/A).This observation suggests a new route for molecular design of electroluminescent polymers as a host fora phosphorescent dopant.