Synthesis and photochromic reactivity of macromolecules incorporating four dithienylethene units
Il Jung,a Hyunbong Choi,a Eunkyoung Kim,b Chai-Ho Lee,c Sang Ook Kang a,*
and Jaejung Ko a,*
a Department of Chemistry,Korea University,Jochiwon,Chungnam339-700,South Korea
b Department of Chemical Engineering,Yoni University134Sinchon-dong,Seodaemoon-gu,Seoul120-749,South Korea
c Department of Chemistry,Wonkwang University,Iksan,Jeonbuk570-749,South Korea
Received11August2005;revid21September2005;accepted22September2005
Available online25October2005
Abstract—Two macrocycles bearing four dithienylethene units were synthesized.Upon irradiation of the macrocycles5and6with ultraviolet light,only one or two photo-induced cyclization reaction occurs.Each isomers were isolated and analyzed by1H NMR spectrum. The quantum yield of5and6are0.58and0.64,
respectively.The high value is due to the prence of enforced antiparallel conformation in the macrocycles5and6.
q2005Elvier Ltd.All rights rerved.
1.Introduction
The conformationally rigid and shape-persistent supra-molecules of nanometer size have attracted much interest becau of their potential in host–guest systems,1fluor-escence ion nsor,2lf-aggregation,3organometallic coordination,4and liquid crystal.5The design of geo-metrically well-defined supramolecules will play an important role becau the incorporation of orientation-ally-controlled functional units into molecules can be utilized as the encoding of information.6The combination of the lf-asmbly and photochromic unit promis to be uful in optical technological devices.7Photochromic1,2-diarylethene is very suitable for this purpo,due to the remarkable thermal stability and high fatigue resistance.8 The open-ring isomer of diarylethene has two confor-mations—antiparallel and parallel—in equal amounts.The conrotatory cyclization can proceed only from the anti-parallel conformation.Therefore,the cyclization quantum yield cannot exceed50%in solution.To achieve high quantum yield,it is required to increa the population of the a
ntiparallel conformers.Thus,diarylethene—backbone photochromic polymer,9multi-dithienylethene arrays,10and diarylethene in the crystal lattice11showed a high cyclization quantum yield due to the geometrical restriction. In a recent development,new dithienylethene bad mono-and multi-substituted phthalocyanine and tetraazaporphyrin hybrids have been introduced in the form of a macrocyclic photochromic system.12We envisioned that the strategic placement of diarylethene units within a macrocyclic framework would achieve high quantum yield becau the macromolecule has the enforced antiparallel conformation of the diarylethene units.We now describe(i)the synthesis of macromolecules having diarylethene units;(ii)their photochromic reactivities;(iii)the isolation of photo-cyclized products.
2.Results and discussion
Our strategy for the synthesis of macrocycles is to incorporate the diarylethene units within a macrocyclic framework.New macromolecules5and6are conveniently synthesized in four steps from the1,2-bis[2-methyl-5-bromo-3-thienyl]perfluorocyclopentene.The palladium-catalyzed cross-coupling of1,3-diethynylbenzene with1 afforded2in53%yield.The Sonogashira coupling of2with 2.2equiv of trimethylsilylacetylene followed by basic hydrolysis yielded4.Our synthesis of macrocycles5and 6was prepared by the cross-coupling reaction of2with4 and coupling reaction13of t
he dialkyne4with trans-Pt(PEt3)2Cl2,respectively(Scheme1).Spectroscopic data for5is completely consistent with its propod structures. Four resonances at2.07,2.06,1.96,and1.95ppm in the1H NMR spectrum and two peaks at15.6and14.5ppm in13C NMR spectrum of5for the methyl group are obrved.
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The
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Tetrahedron61(2005)12256–12263
0040–4020/$-e front matter q2005Elvier Ltd.All rights rerved.
Keywords:Photoswitch;Macrocycle;Diarylethene;High quantum yield.
*Corresponding authors.Tel.:C82418601337;fax:C82418675396;
e-mail:jko@korea.ac.kr
临朐全羊mass spectrum of 5showed a molecular ion at m /z 1760.Compound 6was characterized by 1H,13C,and 31P NMR,mass spectroscopy,and elemental analysis.The initial indication of the macromolecule 6stemmed for the obrvation of an ion in the mass spectrum at m /z 2637.Three peaks in the 1H NMR spectrum (1.96,1.95,and 1.85ppm)and four peaks at 16.5,15.1,9.7,and 8.7ppm in the 13C NMR spectrum of 6proved that a macrocycle is formed in 6.The 31P NMR spectrum of 6shows a singlet at 5.84ppm with a small coupling constant of 1J PtP (2348Hz),which is consistent with the trans configuration of 6.
13
Scheme 1.Reagents and conditions:(i)1,3-diethynylbenzene,Pd(PPh 3)4,CuI in NEt 3;(ii)Me 3SiC ^C
H,Pd(PPh 3)4,CuI in NEt 3;(iii)KOH in MeOH and THF,then H 2O;(iv)2C 4,Pd(PPh 3)2Cl 2,P(o -tolyl)3,CuI in NEt 3;(v)4,trans -Pt(PEt 3)2Cl 2,CuCl in Et 2
NH.
Figure 1.Absorption spectral change of 3in chloroform upon irradiation with 325nm light (---).Total irradiation periods are 0,10,20,30,40,50,60,70,80,I.Jung et al./Tetrahedron 61(2005)12256–1226312257
Figure1shows a typical absorption spectral change of3in chloroform upon ultraviolet light irradiation.Irradiation of chloroform solution of3at325nm light resulted in an immediate increa in the absorption intensity at600nm. After visible light irradiation(l O532nm)for6h,the colored solution was completely bleached.In thefirst120s of irradiation,an absorption band centered at600nm grows in as3is converted from the colourless-open form3(OO)to the blue-clod form3(CO).The prence of an isosbestic point at334nm indicates that3(OO)is cleanly converted to a cond unique photocyclized product.The clod-ring isomer3(CO)was isolated from the blue colored solution by HPLC.The photogenerated ring-clod form3(CO)was stable at room temperature.Figure2shows the1H NMR spectrum of methyl protons of3in CDCl3before photoirradiation and in the ring-clod form,respectively. In the1H NMR spectrum of3(OO),two methyl resonances were obrved at1.83and1.80ppm.In the blue isomer3 (CO),one distinct new band was appeared at2.16ppm, together with two singlets at1.93and1.88ppm,which are slightly down-field shifted to tho of3(OO).The integral ratio of the two signals was1:1,which indicates that the colored isomer is a C–dimer.Another key feature in the1H NMR spectrum of3(CO)is the prence of four thienyl signals at7.24,7.22,6.47,and6.41ppm.The two new resonances at6.47and6.41ppm are significantly up-field shifted as would be expected for the ring-clod isomer.Such an up-field shift was obrved in covalently linked double1,2-dithienylethenes.10a The dissymmetric nature of the photogenerated pro
灵泽duct indicates that only one of the thienyl units has cyclized to form3(CO)(Scheme2).The fluorescence band of3(OO)(l Z420nm)shows a substantial spectral overlap with the absorption band of3 (CO),and the Fo¨rster excitation energy transfer can take place from the photogenerated3(OO)to the colored form3 (CO).Accordingly,the cyclization reaction of another open-ring form cannot take place.A similar result has been obrved in the thienylethene dimer.10
Figure3shows the absorption spectral change of the macromolecule5in chloroform by photoirradiation.Upon irradiation with325nm light,the colourless solution of the open-ring isomer5(OOOO)with the absorption maximum at313nm turned blue,in which characteristic absorption maximum was obrved at602nm.Upon visible (l O532nm)light irradiation,the blue color was completely bleached.
The photogenerated products were analyzed with HPLC chromatograph(silica gel column,eluent:hexane/ethyl acetate4:1).When monitored at the isosbestic point of 338nm,three peaks were obrved.Thefirst peak isomer had the absorption maximum at610nm,while the absorption maximum of the cond peak isomer was
shifted
Figure2.1H NMR methyl signals of(a)the3(OO)dimer;and(b)the3(CO)dimer.
I.Jung et al./Tetrahedron61(2005)12256–12263
12258
狼的组词to 602nm.The three isomers were isolated and analyzed by 1
H NMR.Figure 4shows the 1H NMR spectra of methyl protons of 5in CDCl 3before photoirradiation and in the ring-clod forms.The methyl protons of the first peak isomer show ven resonances at 2.18,2.16,2.07,2.05,1.96,1.94,and 1.92ppm.The first two signals at 2.18and 2.16ppm are assigned to the methyl protons of the clod-ring form.Other five signals are ascribed to the open-ring form.A
characteristic feature in the 1H NMR spectrum includes four singlets at 7.17,7.13,7.09,and 6.48ppm in the region of thienyl protons.The new signal at 6.48ppm is assigned to the proton of clod-ring thienyl unit.This indicates that the first peak isomer is due to the isomer having one clod-ring form 5(COOO)(Scheme 3).The methyl protons of the cond peak isomer show five resonances at 2.17,2.07,2.05,1.97,and 1.95ppm.The signal at 2.17ppm is assigned to the protons of the clod-ring form.The integral ratio of a signal at 2.17ppm
with
Figure 3.Absorption spectra of 5(OOOO)(—),5(COOO)(–$–$–),and 5(COCO)(---)in the photostaionary state under irradiation with 325nm light,and fluorescence spectrum of 5(OOOO)(—)in
chloroform.
Figure 4.1H NMR methyl signals of the (a)5(OOOO);(b)5(COOO);and (c)5
(COCO).
I.Jung et al./Tetrahedron 61(2005)12256–1226312259
other signals is approximately 1:1.In addition,there are four distinct bands at 7.13,7.09,6.72,and 6.52ppm in the thienyl region,in which the signals at 6.72and 6.52ppm is assigned to the clod-ring thienyl units.This indicates that two clod-ring form units are included in the macro-molecule 5(COCO).The methyl protons of the third peak isomer are identical to tho of the open-ring form isomer 5(OOOO).Excitation of 5(OOOO)at 315nm results in light emission with a maximum at 430nm.Due to the spectral overlap of the fluorescence peak of 5(OOOO)and
absorption peak of 5(COCO),followed by the Fo备胎攻略
¨rster excitation energy transfer,the cond peak isomer has the 5(COCO)form.Such excited energy transfer is considered to prohibit the formation of further clod-ring form (Scheme 4).
Figure 5shows the absorption spectra of 6in chloroform before photoirradiation and in the photostationary state under irradiation with 325nm light.Irradiation of chloro-form solution of 6at 325nm light resulted in an immediate increa in the absorption intensity at 628nm.The absorption maximum shifts to longer wavelength by
26nm in comparison with 5.Upon exposure of the dark blue solution to the visible light (l O 532nm)for 3min,the colored solution was completely bleached.In the photo-stationary state,88%of 6is converted into the clod form.The clod-ring isomer 6(COCO)is stable and isolated from the blue colored solution by HPLC.Figure 6shows the 1
H NMR spectra of methyl protons of 6in CDCl 3before photoirradiation and in the ring-clod form.Before photoirradiation,three resonances are obrved at 1.96,1.95,and 1.85ppm.In the ring-clod form,one new resonance appears at 2.14ppm along with a decrea of the intensity of the three resonances.The strong one resonance at 2.14ppm is assigned to the methyl protons of the clod form.No side reaction was detected from the 1H NMR spectra.
The quantum yield of this macromolecules 5and 6are measured using 1,2-bis(2-methyl-3-thienyl)perfluorocyclo-pentene (TF 6)as a reference.14The cyclization quantum yield of 5from the all open-ring form 5(OOOO)to the 5(COOO)isomer and form 5(COOO)to the 5(COCO)isomer was determined to be 0.33and 0.25,
respectively.
Scheme 4.The photochromic reactivity of 6正在营业
钱塘江大潮怎么形成的.
Figure 5.Absorption spectral change of 6in chloroform upon irradiation with 325nm light.Total irradiation periods are 0,10,20,30,40,50,60,70,80,90,I.Jung et al./Tetrahedron 61(2005)12256–12263
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