CA2664445A1 - Aromatic ether-containing spirofluorenexanthene monomers, methods for their preparation and polymerization thereof - Google Patents

Abstract

Novel aromatic ether-containing spirofluorenexanthene monomers (AE-SFX) are described along with processes for their preparation and their polymerization into corresponding aromatic ether-containing poly(spirofluorenesxanthenes) (AE-PSFX). These polymers exhibited stable blue-emission and therefore have application in polymer light-emitting devices.

Description

B&P Ref. 11157-196/PF
TITLE: AROMATIC ETHER-CONTAINING SPIROFLUORENEXANTHENE
MONOMERS, METHODS FOR THEIR PREPARATION AND
POLYMERIZATION THEREOF

FIELD OF THE DISCLOSURE
The present disclosure relates to aromatic-ether containing spirofluorenexanthene monomers and polymers derived therefrom. The present disclosure further relates to uses of the novel aromatic-ether containing poly(spirofluorenexanthenes) as materials for photoluminescence and electroluminescence in light emitting devices.
BACKGROUND OF THE DISCLOSURE
Luminescent organic materials have long been the focus of intense academic and industrial research and are currently being investigated in applications ranging from organic light-emitting diodes, organic photovoltaics, organic thin-film transistors, lasers and sensors. To meet these demands, high-molecular-weight blue-emitting poly(p-phenylene) (PPP) materials including, ladder-type PPPs, polyfluorenes (PF), polyindenofluorenes (PIFs), and polytetrahydrophenanthrene (PTHP) are being extensively studied.' Alkyl-substituted PFs are promising materials, in particular, the dioctyl-substituted polymer (polydioctylfluorene, PFO) is the "work-horse" material in this field.' While PF materials are strong candidates for optoelectronic applications, their spectral instability or their tendency to exhibit green emission upon thermal stress remains a significant challenge, and could limit the realization of their full potential.
The origin of PFs spectral instability has been attributed to morphological and/or oxidative instability, resulting in low-energy excimer or fluorenone-based emission respectively.2 A variety of approaches toward achieving color purity have appeared in the literature and include, but are not limited to, monomer purification,3 polymer blending ,4 nanoparticle doping 15 copolymerization, 10- 11 incorporation of sterically demanding groups,12 functionalization with thermally stable13-17 and spiro-moieties. 18-20 Spiro-containing materials, in which a common spa-hybridized atom links two orthogonally oriented n-systems, have been shown to stabilize blue-emission in low-molecular-weight spirobifluorene (SBF) compounds by blocking efficient crystallization from the amorphous state.21 This success has led to the incorporation of Spiro moieties into polymeric systems such as polyspirobifluorene22-29 (PSBF) and polyspiroanthracenefluorene18. 30, 31 (PSAF), resulting in increased spectral stability. In addition to PSBF and PSAF polymers, a new class of blue-emitting low-molecular-weight spirofluorenexanthene'9 (SFX) and high-molecular-weight poly(spirofluorenexanthene)20 (PSFX) materials, prepared through one-pot methodologies, have recently appeared in the literature. These xanthene-containing materials have only recently appeared due to a limited number of reports outlining their efficient synthesis. Consequently, detailed studies of SFX and PSFX material properties are limited.19 20 Xie et a!. reported a one-pot synthesis in which a one step condensation reaction of 2,7-dibromo-9-fluorenone in the presence of phenol and methanesulfonic acid at high temperatures (ca. 150 C) yielded spiro[fluorene-9,9'-xanthene], SFX.19 A low molecular-weight blue-emitting material prepared from SFX displayed good oxidative stability after annealing for 12 hours at 150 C. However, no high-molecular-weight polymers were reported. Consequently, it remains unknown if the oxidative stability of the low-molecular-weight material will be manifested in the polymer.19 In another recent report, Tseng et a!. were able to prepare alkyl-substituted high-molecular-weight poly[spiro(fluorene-9,9'-xanthene)], PSFX. They conducted a one-step condensation reaction of 2,7-dibromo-9-fluorenone with resorcinol in the presence of ZnCI2/HCI to prepare the monomer. Subsequent polymerization yielded polymers of limited solubility in common organic solvents.20 Thermal properties were investigated by thermogravimetric analysis (TGA) revealing 5 and 10 % weight losses of 411 and 433 C respectively. Thermal annealing studies conducted under a nitrogen environment showed no long wavelength emission. However, ambient studies were not reported, therefore, their oxidative stability is unknown.

SUMMARY OF THE DISCLOSURE
In an effort to prepare PFs with increased oxidative stability, and consequently increased spectral stability the introduction of aromatic-ethers (AE) at the 9,9' position was conducted. In an effort to prepare AE-containing PFs utilizing a methodology developed for preparing phenol substituted fluorenes33, it was discovered that combining 2,7-dibromo-9-fluoreneone with 1,3-diphenoxybenzene in the presence of methanesulfonic acid and a catalytic amount of 3-mercaptopropionic acid led directly to an AE-substituted SFX species 2,7-dibromo-spiro(fluorene-9,9'-(2'-phenoxyxanthene)).
Subsequent polymerization afforded an AE-substituted PSFX material, poly[spiro(fluorene-9',9'-xanthene)], possessing excellent solubility in common organic solvents and excellent thermal and oxidative stability.
Accordingly, the present disclosure includes novel aromatic ether-containing spirofluorenexanthene (AE-SFX) monomers of the Formula I:

X x I
on O
& (R)o wherein X is a polymerization-enabling leaving group;
R is simultaneously or independently selected from C1_6alkyl, fluoro-substituted-C1_6alkyl, -O-CI_6alkyl, fluoro-substituted-O-C1_6alkyl, aryl and fluoro-substituted-aryl; and ois0, 1,2,3,4or5.
There is also included in the present disclosure a method for the preparation of compounds of Formula I:

x x no 0 (R)o (I) wherein X is a polymerization-enabling leaving group;
R is simultaneously or independently selected from C1_6alkyl, fluoro-substituted-C1_6alkyl, -0-C1.6alkyl, fluoro-substituted-O-CI_6alkyl, aryl and fluoro-substituted-aryl; and ois0, 1,2,3,4 or 5, comprising:
(a) reacting a compound of the Formula II:

X_1Z x 0 (II) wherein X is a polymerization-enabling leaving group, with a compound of the Formula III:

a o o & (R)o (III), wherein R is simultaneously or independently selected from C1.6alkyl, fluoro-substituted-C1-6alkyl, -O-C1.6alkyl, fluoro-substituted-O-C1.6alkyl, aryl and fluoro-substituted-aryl; and ois0, 1, 2,3,4or5, in the presence of an acid under conditions to form the compound of the Formula I.
In a further embodiment of the present disclosure, there is included an aromatic-ether-containing poly(spirofluorenexanthene) (AE-PSFX) comprising repeating monomeric units of the Formula IV:

~ I I Nz~
O o (R)o wherein R is simultaneously or independently selected from C1.6alkyl, fluoro-substituted-C1_6alkyl, -O-C1.6alkyl, fluoro-substituted-O-C1.6alkyl, aryl and 5 fluoro-substituted-aryl; and o is 0, 1, 2, 3, 4 or 5.
It another embodiment of the present disclosure, there is included an AE-PSFX of the Formula V:

(R')m~ (R')m n\
\ I I /
O

(R)o (V) wherein R1 is C1-6alkyl;
R is simultaneously or independently selected from C1.6alkyl, fluoro-substituted-C1_6alkyl, -O-C1.6alkyl, fluoro-substituted-O-C1_6alkyl, aryl and fluoro-substituted-aryl;
n is an integer between 1 and 10,000;
m is 0, 1, 2, 3, 4 or 5; and ois0, 1,2,3,4or5.
In yet another embodiment of the present disclosure, there is included a light-emitting solid state device comprising an AE-PSFX of the present disclosure.
Other features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the disclosure are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure will become apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosure will now be described in greater detail with reference to the following drawings in which:
Figure 1 shows an ORTEP drawing of I(a) (AE-SFX). Ellipsoid probability is 20 %.
Figure 2 shows UV-vis absorption and photoluminescence spectra ( X= 350 nm) of a toluene solution of V(a) (AE-PSFX).
Figure 3 shows TGA curves of V(a) (AE-PSFX) and PFO under a N2 atmosphere at a heating rate of 10 C/min.
Figure 4 shows PL spectra (XeX= 350 nm) of a film of V(a) (AE-PSFX) before (blue) and after annealing at 200 C for 20 h (red), 40 h (yellow), 60 h (black), and 80 h (green) under an argon atmosphere.
Figure 5 shows PL spectra of a film of V(a) (AE-PSFX) before (blue) and after annealing for 1 h (green), 2 h (yellow), and 3 h (red) at 150 C
under ambient conditions.
Figure 6 shows PL spectra (XX= 350 nm) of a PFO film before (blue) and after annealing for 20 minutes (green), 40 minutes (yellow), and 60 minutes (red) at 150 C under ambient conditions.
DETAILED DESCRIPTION OF THE DISCLOSURE
(I) DEFINITIONS
The term "C1_6alkyl" as used herein refers to straight or branched chain alkyl groups containing from one to six carbon atoms and includes, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, n-hexyl, isopentyl, and the like.
The term "aryl" as used herein means a monocyclic, bicyclic or tricyclic carbocyclic ring system and optionally a metal and includes phenyl, naphthyl, anthracenyl, 1,2-dihydronaphthyl, 1,2,3,4-tetrahydronaphthyl, fluorenyl, indanyl, indenyl, ferrocenyl, and the like.
In understanding the scope of the present disclosure, the term "comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives. Finally, terms of degree such as "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least 5% of the modified term if this deviation would not negate the meaning of the word it modifies.
(II) MONOMERS OF THE DISCLOSURE
The present disclosure includes novel AE-SFX monomers of the Formula I:

X Q / \ x Nz~
on 0 6:7,4 (R) 0 (I) wherein X is a polymerization-enabling leaving group;
R is simultaneously or independently selected from C1_6alkyl, fluoro-substituted-C1.6alkyl, -O-C1-6alkyl, fluoro-substituted-O-C1_6alkyl, aryl and fluoro-substituted-aryl; and o is 0, 1, 2, 3, 4 or 5.
In an embodiment of the disclosure, X is bromo.
In a further embodiment R is H.
The present disclosure relates to a method for the preparation of the monomers of Formula I. It has been found that reacting 2,7-dibromo-9-fluroeneone with 1,3-diphenoxybenzene in the presence of an acid and a catalyst leads directly to an AE-substituted spirofluorenexanthene (AE-SFX) compound.
Accordingly, there is also included in the present disclosure a process for the preparation of compounds of Formula I:

x no 0 6:1:4 (R)o (I) wherein X is a polymerization-enabling leaving group;
R is simultaneously or independently selected from C1_6alkyl, fluoro-substituted-C,_6alkyl, -O-C1_6alkyl, fluoro-substituted-O-CI_6alkyl, aryl and fluoro-substituted-aryl; and o is 0, 1, 2, 3, 4 or 5.
comprising:
(a) reacting a compound of the Formula II:

x x 0 (II) wherein X is a polymerization-enabling leaving group, with a compound of the Formula III:

C ~
o o / i (R)o (Ill), wherein R is simultaneously or independently selected from C1_6alkyl, fluoro-substituted-C1-6alkyl, -O-C1.6alkyl, fluoro-substituted-O-C1.6alkyl, aryl and fluoro-substituted-aryl; and ois0, 1, 2,3,4or5, in the presence of an acid and a catalyst under conditions to form the compound of the Formula I.
In an embodiment of the disclosure, the acid is a sulfonic acid, such as methane sulfonic acid and the catalyst is a mercapto acid, such as 3-mercapto-propionic acid.
In an embodiment of the disclosure, the conditions to form a compound of the Formula I comprise reacting the compounds of Formulae II and III in the presence of the acid and catalyst, suitably neat, at a temperature of about 40 C to about 100 C for about 12 hours to about 36 hours. In a further embodiment, the compound of Formula III is used in excess amounts, for example, in at least a 10 fold excess. In a further embodiment, the acid is used in excess amounts. In another embodiment the catalyst is used in catalytic amounts.

(III) POLYMERS OF THE DISCLOSURE
The direct incorporation of AE functionality into SFX-containing materials from readily available starting materials has allowed for the preparation of a high-molecular-weight, room-temperature soluble, thermally stable material with good oxidative stability. This is the first report of a highly soluble PSFX material exhibiting excellent thermal and oxidative stability.
Accordingly, the present disclosure includes an aromatic-ether-containing poly(spirofluorenexanthene) (AE-PSFX) comprising repeating monomeric units of the Formula IV:

6-1-311 (R) (IV) wherein R is simultaneously or independently selected from C1.6alkyl, fluoro-substituted-C1_6alkyl, -O-C1.6alkyl, fluoro-substituted-O-C1 alkyl, aryl and fluoro-substituted-aryl; and o is 0, 1, 2, 3, 4 or 5.
5 It another embodiment of the present disclosure, there is included an AE-PSFX of the Formula V:

(R1)m\r\ \ ~j(R1)m n \ I I /
O O

(R)o (V) wherein R1 is C1_6alkyl;

10 R is simultaneously or independently selected from C1_6alkyl, fluoro-substituted-C1.6alkyl, -O-C1_6alkyl, fluoro-substituted-O-C1.6alkyl, aryl and fluoro-substituted-aryl;
n is an integer from 1 to 10,000;
m is 0, 1, 2, 3, 4 or 5; and o is 0, 1, 2, 3, 4 or 5.
In an embodiment of the R' is methyl or ethyl, suitably methyl and m is 1, 2 or 3, suitably 2. In a further embodiment of the disclosure, m is 2 and the 2 R1 groups are located at the 3 and 5 positions of the phenyl ring.
The value of n varies as desired to achieve desired properties such as solubility, processibility, formability and the like as would be known to a person skilled in the art. In an embodiment of the disclosure, the n is an integer that provides a weight average molecule weight (Mw) of about 100,000 to about 200,000.
In a further embodiment the polymers of Formula V are prepared by polymerizing the monomers of Formula I under Yamamoto coupling conditions (see ref. 35) initiated in a microwave reactor. It is appreciated that any end-capping agent can be used in the polymerization reaction. Such agents are known to those skilled in the art. In another embodiment the polymers of Formula V possess a mono-modal molecular weight distribution and a polydispersity index of greater than 1.0, for example between 2.0 and 5Ø
In a further embodiment of the disclosure, the AE-PSFX of the Formula V is:

/ \ \ / \ /

6 (Va) wherein n is an integer between 1 and 10,000.
In an embodiment of the disclosure the AE-PSFX are homopolymers.
In a further embodiment the AE-PSFX are copolymerized with other monomers. Usually copolymerization is used to reduce the cost of materials by reducing the fluorene content. Representative comonomeric materials include olefin units such as ethylene, propylene and the like, aromatic units such as styrene and the like and ester units. If comonomeric units are present, the leaving groups X, are selected to accommodate the additional comonomers in the polymerization. The relative weight proportion of the comonomeric units will range from 100:0 (for pure polyfluorene homopolymer) to aboit 10:90 for a highly diluted material.
Compound V(a), shown above, exhibited greater thermal stability, with 5 and 10 % weight loss values of 536 and 577 C respectively, in comparison to PFO, with 5 and 10 % weight loss values of 404 and 420 C respectively, indicating AE moieties substantially improve the thermal and oxidative stability of PFs.
Thermal annealing of a film of compound V(a) for 20, 40, 60 and 80 hours in an argon filled glove-box demonstrated its spectral stability. As expected, thermal processing leads to small spectral variations in the region of 400-500 nm. The stable blue-emission and the absence of a green emission band after prolonged heating highlights the stability of V(a) to excimer formation. Identical thermal stresses were applied to PFO so as to directly compare the two materials. A film of PFO subjected to the same conditions clearly illustrates its spectral instability; exhibiting an increase in intensity at - 550 nm which we attribute to excimer formation (Figure 5).36, Therefore, thermal annealing under an argon atmosphere demonstrates the improved spectral stability of the AE-PSFX polymers of the present disclosure in contrast to PFO.
To investigate the oxidative stability of the AE-PSFX polymers of the present disclosure when thermally stressed, a drop-coated film of V(a) was heated on a hot plate at 150 C, under ambient conditions, for predetermined periods of time, and followed the evolution of its photoluminescence spectra.
As illustrated in Figure 5, V(a) continued to display a strong blue-emission after three hours of annealing, and a substantially smaller increase in green-emission at - 550 nm in contrast to PFO (Figure 6). Of particular note and for comparison purposes, the present V(a) shows a weak green emission after 1 hour whereas PFO shows an intense green emission (ca. 550 nm) after only minutes of annealing.
In yet another embodiment of the present disclosure, there is included 20 a light-emitting solid state device comprising an aromatic-ether containing poly(spirofluorenexanthene) of the present disclosure, i.e. an an AE-PSFX
comprising repeating monomeric units of the Formula IV or an AE-PSFX of the Formula V. In an embodiment, the light-emitting solid state device is configured as a light-emitting diode or a light-emitting electrochemical cell.
The following non-limiting examples are illustrative of the present disclosure:
EXAMPLES
General Information:
Chemicals: All reagents and solvents were purchased from commercial sources and used without further purification unless specified, concentrated HCI (EMD); Ni(COD)2 98% (Strem); 2,7-dibromofluorene (Alfa Aesar); DMF
and acetic anhydride (Caledon); diethylether, methanol, acetone, and ethyl acetate (Fisher); Chromium(VI) oxide 99.9 %, toluene, 1,3-diphenoxybenzene 99 +%, 5-bromo-m-xylene 97 %, 1,5-cyclooctadiene > 99 % (COD) freeze/pumped thawed three times and 2,2-dipyridyl (BPY) > 99 % dried on Schlenk line for 16hrs (Aldrich); 2,7-dibromofluorene-9-one was prepared according to literature procedures.`
Procedures: 'H-NMR and 13C-NMR spectra of AE-PSFX were recorded on a Varian Inova 500 (500 MHz and 125 MHz respectively) spectrometer and 1H-NMR and 73C-NMR spectra of AE-SFX were recorded on a Varian Inova 400 (400 MHz and 100 MHz respectively) spectrometer. Elemental analysis was performed using a Carlo Erba CHNS-O EA1108 elemental analyzer.
Photoluminescence (PL) spectra were obtained using a Varian Cary Eclipse Fluorescence Spectrophotometer. Low and high resolution mass spectrometry was performed with an Applied Biosystems Voyager Elite MALDI-TOF system and a Kratos Analytical MS-50 electron impact instrument respectively. TGA analysis was performed on a Perkin Elmer Pyris 1 at a heating rate of 10 C/min. GPC was performed on an Agilent 1100 series system equipped with a Waters Styragel HR 4E column. X-ray crystallographic data for AE-SFX were collected on a Bruker PLATFORM/SMART 1000 CCD diffractometer and graphite-monochromated A(Mo Ka) radiation (A = 0.71073 A).
Example 1: 2, 7-Dibromospiro[fluorene-9, 9 -(2'-phenoxyxanthene] AE-SFX 1(a) 2,7-dibromofluorenone (1.13 g, 3.34 mmol) and 1,3-diphenoxybenzene (8.77 g, 33.4 mmol) were added to a 100 mL round bottom flask and heated to 65 C. 3-mercaptopropionic acid (0.0140 g, 0.1 mmol), dissolved in 5 mL of methanesulfonic acid, was added to the yellow/orange melt. The resulting suspension was heated for 20 hours before being poured into distilled water (150 mL) giving an orange precipitate. The precipitate was transferred to a mortar and pestle, ground to a fine powder under water, collected over a Buchner funnel, washed with distilled water (200 mL) and allowed to dry. The dried precipitate was isolated from excess 1,3-diphenoxybenzene by stirring a suspension of precipitate / 100 % ethanol (200 mL) for two hours. The ethanol was decanted and the precipitate resuspended in 100 % ethanol (200 mL) and stirred for an additional hour. The precipitate was collected over a Buchner funnel and washed with 100 % ethanol (100 mL) resulting in a white powder (1.46 g, 52 %). 1H-NMR (400 MHz, CDCI3): 6 7.63 (d, J = 8.1 Hz, 2 H); 7.51 (dd, J = 8.1, 1.7 Hz, 2 H); 7.38 (m, 2 H); 7.29 (d, J = 1.7 Hz, 2 H);
7.21 (m, 2 H); 7.16 (m, 1 H); 7.09 (m, 2 H); 6.83 (m, 2 H); 6.50 (dd, J = 8.7, 2.7 Hz, 1 H); 6.40 (dd, J = 7.8, 1.5 Hz, 1 H); 6.33 (d, J = 8.8 Hz, 1 H) . 13C-NMR (100 MHz, CDCI3): 6 157.92, 156.55, 156.05, 151.85, 150.91, 137.48, 131.33, 129.83, 129.00, 128.83, 128.64, 127.79, 123.99, 123.67, 123.02, 122.42, 121.38, 119.79, 117.25, 117.04, 113.93, 106.14, 54.00. HRMS Calcd for C31H18Br2O2: 581.96533. Found: 581.96570. Anal. Calcd. For C31H18Br2O2:
C, 63.94; H, 3.12. Found: C, 64.23; H, 3.08.
Example 2: Poly[spiro(fluorene-9, 9' (2'-phenoxyxanthene)] AE-PSFX V(a) Ni(COD)2 (0.145 g, 0.529 mmol), BPY (0.083 g, 0.529 mmol), COD (0.06 mL, 0.529 mmol) was dissolved in a DMF (3.3 mL) / toluene (7.0 mL) solution resulting in an opaque purple solution. The solution was heated at 80 C
under an argon atmosphere for 30 minutes and subsequently transferred by cannula to a shlenck flask containing AE-SFX (0.200 g, 0.343 mmol). The dark red solution was maintained at 80 C for 72 hours at which time 5-bromo-m-xylene (0.05 mL, 0.283 mmol) was added and allowed to react for a further 24 hours. The purple slurry was poured into methanol (140 mL) resulting in a gray-colored solid suspended in an opaque pale-blue solution.
The solid underwent a soxhlet wash with acetone for 10 hours and a toluene soxhlet extraction for 8 hours before removing the toluene under reduced pressure resulting in a yellow film (82.0 %). 1H-NMR (500 MHz, CDCI3): 6 7.77 (m, 2 H); 7.52 (m, 2 H); 7.46-7.31 (m, 6 H); 7.28-7.13 (m, 4 H); 7.13-7.00 (m, 3 H); 6.93-6.73 (m, 3 H); 6.59-6.33 (m, 4 H). 13C-NMR (125 MHz, CDC13):
b 157.57, 156.32, 156.03, 152.17, 151.29, 141.16, 138.50, 129.85, 129.15, 128.14, 127.21, 124.79, 124.06, 123.89, 123.64, 120.25, 119.77, 119.37, 119.07, 116.83, 113.89, 106.05, 54.15.

Results and Discussion for Examples I and 2:

(a) Synthesis and characterization of AE-SFX 1(a). As illustrated in Scheme 1, reacting 2,7-dibromofluorene-9-one34 with a 10-fold excess of 1,3-diphenoxybenzene allowed for the preparation of AE-SFX. After isolating a 5 white powder, suitable single crystals were grown for single-crystal X-ray diffraction (Figure 1). Of particular note, the orthogonal disposition of the fluorene and xanthene ring systems, along with the asymmetry generated by the lone aromatic-ether group, should lead to increased solubility of the polymer. The structure was also confirmed with 1H NMR and 13C NMR
10 spectroscopy. The aromatic hydrogen and carbon atoms were readily assigned by analysis of the 1H and 13C NMR spectra as well as 2D NMR
experiments, including 1H-1H correlation spectroscopy ('H-COSY) and long range (HMBC) and short-range (HMQC) 1H-13C hetero-nuclear correlation spectroscopy. In addition, high resolution mass spectrometric data and 15 elemental analysis support the structure.
Scheme 1:

Cr03 Br Br Br acetic anhydride Br O
1,3-diphenoxybenzene methanesuifonic acid 3-mercaptopropionic acid 65 C for 20 hrs Me me NI(COD)2 Br Br \ \ / n \ DMF I Toluene -112 Me Me 80 C for 72 hrs O 0 5-bromo-m-xylene O O
80 C for 24 hrs AE-PSFX
AE-SFX
82% 52%
Mõ = 34 000 Mrõ=147000 n = 80-348 (b) Synthesis and Characterization of AE-PSFX V(a). Subsequent polymerization of AE-SFX under Yamamoto coupling conditions35 produced blue-emitting poly[spiro(fluorene-9,9'-(2'-phenoxyxanthene)] AE-PSFX
polymers, as shown in Scheme 1. In contrast to other reports of PSFX
materials19, 20, AE-PSFX is very soluble at room temperature in common organic solvents such as chloroform, toluene, and THE. Gel-permeation chromatography (GPC) of AE-PSFX shows a mono-modal molecular weight distribution with a number average molecular weight (Mn) of 34 000 and weight average molecular weight (Mw) of 147 000. This corresponds to Mn and Mw degree of polymerizations of approximately 80 and 348 respectively and a polydispersity index (PDI) of 4.3. The high polydispersity may play a role in the observation of increased solubility in common organic solvents.
The polymer was also characterized by 1H NMR and 13C NMR spectroscopy.
(c) Optical and Thermal/Oxidative properties of AE-PSFX V(a) (i) UV-vis absorption and photoluminescence of AE-PSFX V(a). The absorption and photoluminescence (PL) spectra of a 0.0005 % w/v toluene solution of AE-PSFX V(a) are consistent with PF type materials; the absorption maximum and the 0-0 PL vibronic transition occur at 396 nm and 419 nm respectively (Figure 2).
(ii) Thermal stability of AE-PSFX V(a). The thermal stability of AE-PSFX V(a) was investigated by TGA under a nitrogen atmosphere at a heating rate of 10 C/min, as shown in Figure 3. AE-PSFX V(a) exhibits greater thermal stability, with 5 and 10 % weight loss values of 536 and 577 C respectively, in comparison to PFO, with 5 and 10 % weight loss values of 404 and 420 C
respectively.
(iii) Photoluminescence stability of AE-PSFX V(a) under thermal stress. To investigate the spectral stability of AE-PSFX when thermally stressed, studies were conducted in an argon filled glove-box and followed the evolution of its photoluminescence spectra when heated to 200 C. Figure 4 illustrates the normalized PL spectra of an AE-PSFX V(a) film drop-coated from a 0.5 % w/v toluene solution onto a quartz disc. Thermal annealing of the film for 20, 40, 60 and 80 hours in an argon filled glove-box demonstrates its spectral stability. As expected, thermal processing leads to small spectral variations in the region of 400-500 nm. The stable blue-emission and the absence of a green emission band after prolonged heating highlights the stability of AE-PSFX V(a) to excimer formation. Identical thermal stresses were applied to PFO so as to directly compare the two materials. A film of PFO subjected to the same conditions clearly illustrates its spectral instability; exhibiting an increase in intensity at - 550 nm which we attribute to excimer formation (Figure 5).36. 37 Therefore, thermal annealing under an argon atmosphere demonstrates the improved spectral stability of AE-PSFX V(a) in contrast to PFO.
(iv) Photoluminescence stability of AE-PSFX V(a) under thermal oxidative stress.
To investigate the oxidative stability of AE-PSFX V(a) when thermally stressed, a drop-coated film of AE-PSFX V(a) was heated on a hot plate at 150 C, under ambient conditions, for predetermined periods of time, and followed the evolution of its photoluminescence spectra. As illustrated in Figure 5, AE-PSFX V(a) continued to display a strong blue-emission after three hours of annealing, and a substantially smaller increase in green-emission at - 550 nm in contrast to PFO (Figure 6). Based upon the present observation that no green emission arises upon thermal stressing in inert atmosphere (vide supra), it is proposed that this spectral change does not arise solely from excimer formation, and that an as-of-yet unidentified oxidized species gives rise to this emission. Of particular note and for comparison purposes, the present AE-PSFX V(a) shows a weak green emission after 1 hour whereas PFO shows an intense green emission (ca. 550 nm) after only 20 minutes of annealing.
While the present disclosure has been described with reference to what are presently considered to be the preferred examples, it is to be understood that the disclosure is not limited to the disclosed examples. To the contrary, the disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

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Claims (13)

1. An aromatic ether-containing spirofluorenexanthene (SFX) monomer of the Formula I:

wherein X is a polymerization-enabling leaving group;
R is simultaneously or independently selected from C1-6alkyl, fluoro-substituted-C1-6alkyl, -O-C1-6alkyl, fluoro-substituted-O-C1-6alkyl, aryl and fluoro-substituted-aryl; and o is 0, 1, 2, 3, 4 or 5.

2. The monomer according to claim 1, wherein X is bromo.

3. A method for preparing the monomers according to claim 1 or 2, comprising:
(a) reacting a compound of the Formula II:
wherein X is a polymerization-enabling leaving group, with a compound of the Formula III:

wherein R is simultaneously or independently selected from C1-6alkyl, fluoro-substituted-C1-6alkyl, -O-C1-6alkyl, fluoro-substituted-O-C1-6alkyl, aryl and fluoro-substituted-aryl; and o is 0, 1, 2, 3, 4 or 5, in the presence of an acid under conditions to form the compound of the Formula I.

4. The method according to claim 3, wherein the acid is a sulfonic acid and the catalyst is a mercapto acid.

5. The method according to claim 3 or 4, wherein the conditions to form a compound of the Formula I comprise reacting the compounds of Formula II
and III in the presence of the acid and catalyst, suitably neat, at a temperature of about 40 °C to about 100 °C for about 12 hours to about 36 hours.

6. The method according to any one of claims 3-5, wherein the compound of Formula III is used in excess amounts and the acid is used in excess amounts.

7. An aromatic-ether-containing poly(spirofluorenexanthene) (AE-PSFX) comprising repeating monomeric units of the Formula IV:

wherein R is simultaneously or independently selected from C1-6alkyl, fluoro-substituted-C1-6alkyl, -O-C1-6alkyl, fluoro-substituted-O-C1-6alkyl, aryl and fluoro-substituted-aryl; and o is 0, 1, 2, 3, 4 or 5.

8. An AE-PSFX of the Formula V:

wherein R1 is C1-6alkyl;
R is simultaneously or independently selected from C1-6alkyl, fluoro-substituted-C1-6alkyl, -O-C1-6alkyl, fluoro-substituted-O-C1-6alkyl, aryl and fluoro-substituted-aryl;
n is an integer from 1 to 10,000;
m is 0, 1, 2, 3, 4 or 5; and o is 0, 1, 2, 3, 4 or 5.

9. The AE-PSFX according to claim 8, wherein R1 is methyl or ethyl, and m is 1, 2 or 3.

10. The AE-PSFX according to claim 9, wherein m is 2 and the 2 R1 groups are located at the 3 and 5 positions of the phenyl ring.

11. The AE-PSFX according to claim 8, wherein the AE-PSFX of the Formula V is:

wherein is an integer between 1 and 10,000.

12. A light-emitting solid state device comprising an AE-PSFX comprising repeating monomeric units of the Formula IV according to 7 or an AE-PSFX of the Formula V according to any one of claims 8-11.

13. The light-emitting solid state device according to claim 12, configured as a light-emitting diode or a light-emitting electrochemical cell.