Synthesis of Novel Poly(tetramethyl-2,7-silpyrenylenesiloxane) and Its Thermal and Optical Properties

Abstract

KEY WORDS: Pyrene / Poly(tetramethylsilarylenesiloxane) / Heat-Resistant Polymer / Photoluminescence / Pyrene has been well-known to exhibit the good fluorescence property 1 and the unique emission based on its excited dimer in the fluorescence spectrum of the solution at a relatively high concentration (ca. 10 À3 mol/L) and/or of the solid state. Thus, various pyrene derivatives have been used for the emission moiety as an emitting fluorescence probe for biological analyst, electronics and photonics materials such as organic light-emitting diodes (OLEDs) and organic transistor, and so on.2 In addition, the incorporation of silyl substituents onto aromatic species has been reported to result in the high fluorescence quantum yield as well as in the red-shift of maximum absorption wavelength.3 If the silyl substituent is incorporated onto pyrene, the development of the highly efficient fluorophore is presumably promised. On the other hand, polysiloxanes having fluorophore moiety in the main chain have been reported to be obtained as oil products up to now. 4 Thus, the use of polysiloxane derivatives as polymeric OLED materials seems to be inadequate because of their low glass transition temperature (T g ) 5,6 inducing the formation of aggregates, even though the other properties of polysiloxanes such as good thermostability and stability against atomic oxygen 5,6 seem to be appropriate for the polymeric OLED materials. One of the methods for raising T g is incorporation of bulky and rigid moieties into the main chain.7 For example, the T g of poly(dimethylsiloxane) has been reported to be À123 C; 5 however, those of a series of poly(tetramethylsilarylenesiloxane) derivatives to be in the range from À52C to 156 C depending on the arylene moiety introduced. 7-9From these points of view, we report here the synthesis of poly-(tetramethyl-2,7-silpyrenylenesiloxane) (P1) via solution polycondensation of 2,7-bis(dimethylhydroxysilyl)pyrene (M1), as shown in Scheme 1. M1 was prepared by the hydrolysis of 2,7-bis(dimethylsilyl)pyrene (2), which had been obtained by the lithiation reaction of 2,7-dibromopyrene (1) 10 at À78 C followed by the addition of chlorodimethylsilane. M1 underwent polycondensation in chlorobenzene under reflux for 12 h to afford P1. The reaction solution was poured into acetone to isolate P1 as yellow precipitates. The structure of P1 was confirmed by 1 H and 13 C NMR spectroscopy, where each signal was consistently assigned ( Figure S1).P1 is soluble in common organic solvents such as tetrahydrofuran (THF), chloroform, and toluene. The number-average molecular weight (M n ) and the polydispersity index (M w =M n ) of P1 were estimated to be 43000 and 1.38, respectively, by the measurement of size-exclusion chromatography (SEC) of P1 in tetrahydrofuran (THF) eluent using polystyrene standards. The SEC profile of P1 indicated that the obtained polymer was unimodal and that the low-molecular-weight species as a cyclic dimer or trimer were almost completely removed by reprecipitation in acetone.The ther...

Synthesis and properties of poly(tetramethyl-1,6-silpyrenylenesiloxane) derivative with phenyl groups on pyrenylene moiety

“…On the other hand, poly(tetramethylsilarylenesiloxane)s where the aromatic moieties are introduced into the main chain of PDMS have been reported to exhibit the excellent thermostability as well as PDMS and the T g depending on the arylene moieties introduced. Thus, we have reported the synthesis of poly(tetramethylsilarylenesiloxane) derivatives having various aromatic moieties as arylene moieties [2][3][4][5][6]. It has been also reported that these derivatives show bathochromic and hyperchromic effects in the absorption spectra [5,6] by the silyl groups introduced onto aromatic moieties owing to the r*-p* interaction between silyl and aromatic moieties [7][8][9][10][11][12].…”

“…Thus, we have reported the synthesis of poly(tetramethylsilarylenesiloxane) derivatives having various aromatic moieties as arylene moieties [2][3][4][5][6]. It has been also reported that these derivatives show bathochromic and hyperchromic effects in the absorption spectra [5,6] by the silyl groups introduced onto aromatic moieties owing to the r*-p* interaction between silyl and aromatic moieties [7][8][9][10][11][12]. On the other hand, pyrene is one of interesting compounds because it shows excimer emission in the fluorescence spectra at the high concentration and/or in the solid state [13][14][15][16].…”

Synthesis and characterization of poly(tetramethylsilarylenesiloxane) derivatives bearing diphenylfluorene or diphenyldibenzosilole moieties

“…The hyperchromic effects result from the enhancement of the transition moment based on the increase in the dipole moments of the HOMO and LUMO states owing to the s-p conjugation in the HOMO and the s*-p* conjugation in the LUMO. [12][13][14][15][16][17] On the other hand, the 0-0 electronic transition was observed at around 316 nm in the case of silyl-substituted diphenylfluorene derivatives (5, M1 and P1), as shown in Figure 5a, whereas it was observed at around 324 nm in the case of silyl-substituted diphenyldibenzosilole derivatives (6, M2, and P2), as shown in Figure 5b. This bathochromic shift would be due to the stabilization of the LUMO state through s*-p* conjugation induced by the replacement of the C-9 carbon in fluorene by silicon.…”

“…[12][13][14][15][16][17] The bathochromic effect has been known to be induced by lowering the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states because of destabilization of the HOMO state through s-p conjugation and stabilization of the LUMO state through s*-p* conjugation. The hyperchromic effects result from the enhancement of the transition moment based on the increase in the dipole moments of the HOMO and LUMO states owing to the s-p conjugation in the HOMO and the s*-p* conjugation in the LUMO.…”

“…[12][13][14][15][16][17] Kitamura et al 18 reported a polysiloxane having fluorenyl moiety in the main chain; however, the obtained polysiloxane derivative was an oil product owing to the extremely low glass transition temperature (T g ). Thus, the use of polysiloxane derivatives as polymeric OLED materials seems to be inadequate because of their extremely low T g, 19,20 which allows the formation of aggregates and/or interchain excimers to induce the decline of the color stability of light emission.…”