High‐Triplet‐Energy Poly(9,9′‐bis(2‐ethylhexyl)‐3,6‐fluorene) as Host for Blue and Green Phosphorescent Complexes

Abstract

During the last two decades, organic and polymer lightemitting devices (OLEDs/PLEDs) have been the subject of intense academic and industrial research because of their potential applications in full-color flat-panel displays and solid-state lighting. [1][2][3] Recently, phosphorescent PLEDs, in which heavy metal complexes (such as Ir and Pt complexes) are doped into appropriate polymer host materials, have attracted increasing interest owing to the possible full utilization of both singlet and triplet excitons combined with solution processability.[4] Many studies [5] have shown that in order to realize high device efficiency, in phosphorescent PLEDs, the triplet energy state (E T ) of the polymer host should be located at higher energy than that of the guest complexes. Otherwise, triplet excitons on the guest could undergo back-transfer to the triplet state of the host, and as a result the host polymer would become a luminescence quencher of triplet emitters.[6] Since most conjugated polymers have a low-lying triplet state, so far only red-phosphorescent PLEDs with a conjugated polymer as the host have shown high device efficiency. [7] For green-and blue-light-emitting triplet emitters [8] with typically a higher triplet state than that of conjugated polymers, [9] the devices with the conjugated polymer host are poor. Therefore for green-and blue-light-emitting triplet devices, typically nonconjugated poly(vinylcarbazole) (PVK) has been used as the polymer host, since PVK has a relatively high triplet energy state (2.5 eV).[5c] Since PVK is a nonconjugated polymer with high resistivity, typically, the operating voltage of these devices is relatively high. Therefore in order to obtain phosphorescent PLEDs with high efficiency and low power consumption, it is crucially important to develop a wide-bandgap conjugated polymer host with high-lying triplet energy state.The most widely used polymer hosts for fluorescent guest dyes are poly(2,7-fluorene)s and their derivatives, owing to their wide bandgap, high photoluminescence (PL) quantum efficiency, and excellent conductivity.[10] However, many authors have reported that poly(2,7-fluorene)s are not a good host for blue-and green-light-emitting triplet complexes because of their low-lying triplet energy state (2.15-2.3 eV).[5b,5d,6a] Surprisingly, despite poly(2,7-fluorene)s having been investigated for many years, there have been almost no reports on a fluorene homopolymer with fluorene units linked at the 3,6 position. As poly(3,6-carbazole)s [8,11] and poly(3,6-silafluorene)s [12] show higher triplet energy levels than their 2,7-counterparts, we thought it of interest to synthesize poly(3,6-fluorene)s and investigate their photophysical properties. The group of van Dijken and Brunner reported a 3,6-spirofluorene copolymer and oligomers with carbazole. [8a,13] Recently, Mo et al. [14] reported synthesis of poly(3,6-fluorene) by Ni-catalyzed coupling, but their polymer showed a strange and extremely broad PL spectra in the film and neither detailed photophysical p...

Ladder Polysiloxanes for Optoelectronic Applications

“…13, the turn-on voltage of device is 5.8 V, which is lower than that of reported polymer host materials. The device reaches the maximum brightness of 883 cd/m 2 at 13 V and shows a maximum luminous efficiency of 8.7 cd/A or the maximum power efficiency of 3.1 lm/W, which is superior to that of the reported polymer host (9,9 ' -bis(2-ethylhexyl)-3,6-fuorene) (Wu et al, 2008) and PVK, (Kido et al, 1993) even comparable to the small molecule host 4,4 ' -bis(9-carbazolyl)biphenyl (CBP). (Hu et al, 2009) The external quantum of the device is 4.6% ph/el, which is best blue light polymer host for FIrpic reported so far.…”

Synthesis and optoelectronic properties of chemically modified bi-fluorenylidenes

“…2 Their attraction to chemists, physicists and engineers originates not only from the already established high incident-photon-to-current conversion efficiencies and low-cost production but also from the scientific interest in their operational principles. 3 The fabrication of high-performance DSSCs requires the development of efficient organic dyes, whose molecular structures are optimized to provide sufficient light-harvesting features, good electronic communication between the dye and the conduction or valence band of the semiconductor, and a controlled molecular orientation on the semiconductor surface. 4 Due to the almost infinite synthetic versatility and the high potential in molecular design, precise control of the photophysical and electrochemical properties may be achieved by the modification of the chromophore skeleton or the introduction of substituents.…”

A high triplet-energy polymer: synthesis and photo-physical properties of a π-stacked vinyl polymer having a xanthone moiety in the side chain

“…Existing host materials include carbazole derivative, [8][9][10][11][12][13][14] triphenylamine derivatives, 15 triazine derivatives, 16,17 and polyfluorenes. 18,19 However, xanthone-based polymers have not been explored as a triplet host while xanthone has a T 1 energy (3.21 eV) 20, 21 which is higher than that of bluephosphorescent iridium bis [(4,6-difluorophenyl)pyridinato-N,C 2 ]picolinate (FIrpic: T 1 2.65 eV). 9 Herein, we report the synthesis and properties of poly(xanthon-3-yl methacrylate) (poly(XOMA)) and poly(xanthon-3-yl methacrylate-co-methyl methacrylate) (poly(XOMA-co-MMA)) as well as xanthon-3-yl acetate (XA) as a model compound of monomeric unit (Chart 1).…”