Highly Photoluminescent Nonconjugated Polymers for Single-Layer Light Emitting Diodes Zachariah A. Page, † Chien-Yang Chiu, † Benjaporn Narupai, †,‡ David S. Laitar, § Sukrit Mukhopadhyay, § Anatoliy Sokolov, § Zachary M. Hudson, † Raghida Bou Zerdan, † Alaina J. McGrath, † John W. Kramer, § Bryan E. Barton, § and Craig J. Hawker* ,†,‡ † Materials Research Laboratory and ‡ Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States § The Dow Chemical Company, Midland, Michigan 48674, United States * S Supporting Information ABSTRACT: The design, synthesis, and characterization of solution-processable polymers for organic light emitting diode (OLED) applications are presented. Theoretical calculations were employed to identify a carbazole-pyrimidine based building block as an optimized host material for the emissive layer of an idealized OLED stack. Efficient, free radical homopolymerization and copolymerization with a novel methacrylate-based heteroleptic iridium(III) complex leads to a library of nonconjugated polymers with pendant semi- conductors. Optoelectronic characterization reveals impressive photoluminescence quantum yield (PLQY) values exceeding 80% and single-layer OLEDs show optimal performance for copolymers containing 6 mol % of iridium comonomer dopant. KEYWORDS: polymer, photoluminescence quantum yield, phosphorescence, iridium, organic light emitting diode S ince the discovery of electroluminescence in polymeric systems by University of Cambridge researchers, significant efforts have been devoted to the design and synthesis of polymer semiconductors for organic light emitting diode (OLED) applications. 1 This is driven by the identification of OLEDs as a promising solution to the challenge of energy efficient flat panel displays and solid state lighting. 2-6 Although OLEDs constructed from vacuum-deposited small molecule semiconductors currently provide the most efficient devices, polymeric materials offer distinct advantages for commercial manufacturing. These advantages include improved device stability, flexibility, and solution processability that open up large-area and low-cost fabrication techniques (e.g., spin- coating, inkjet printing, roll-to-roll, etc.). From a materials design and efficiency viewpoint, phosphorescent heavy metal complexes are traditionally added to these organic systems as they significantly increase the efficiency of singlet-to-triplet intersystem crossing (ISC) resulting in high emission efficiency from both excited states, which is critical given the generation of a 1:3 singlet:triplet under electrical bias. 7 In selecting a phosphorescent building block, iridium(III) complexes outperform other heavy-metal phosphors due to their impressive photoluminescence quantum yield (PLQY), stability, short triplet state lifetimes, and spectral tunability from blue to near-infrared. 8-13 To suppress concentration quenching and triplet-triplet annihilation, these complexes are tradition- ally added as guests (dopants/emitters) into a host polymer matrix. However, physical blending of semiconducting polymer hosts with Ir III small molecules can lead to poor device lifetimes due to phase separation and subsequent aggregate-induced quenching. 14 Alternatively, covalently binding Ir III to a polymer improves device longevity and provides a one-component emissive material that reduces the complexity associated with simultaneous materials processing, though at the expense of synthetic complexity and building block choice. 15-24 In this report we describe the synthesis of readily available building blocks for high performance, single-layer OLEDs based on a simple comonomer strategy. Design principles for these nonconjugated OLED systems starts with an analysis of energy levels, since they dictate the mechanism by which energy transfer occurs along with emission color. Triplet energy back transfer (from emitter to host) via Dexter transfer has been identified as a common shortcoming among OLEDs. Utilizing a host with a large T 1 (>T 1 of the emitter) 25 or spatially separating the emitter from the host through a nonconjugated spacer are two common methods to reduce energy back transfer. 26 In addition to the relative T 1 energy Received: December 15, 2016 Article pubs.acs.org/journal/apchd5 © XXXX American Chemical Society A DOI: 10.1021/acsphotonics.6b00994 ACS Photonics XXXX, XXX, XXX-XXX