Photochromic and Fluorescent Properties of a Diarylethene Dimer
Kyoko Yagi and Masahiro IrieÃ
Department of Chemistry and Biochemistry,Graduate School of Engineering,Kyushu University, Hakozaki6-10-1,Higashi-ku,Fukuoka812-8581
(Received May28,2003;CL-030467)
A diarylethene dimer connected with a diyne1(O–O)was synthesized.Upon irradiation with350-nm light the colorless hexane solution of1(O–O)changed to a dark-blue solution, in which absorption maximum was observed at574nm.The color is due to the formation of the isomer having one closed-ring form1(O–C).1(O–C)emitted redfluorescence at 720nm and the intensity reversibly changed along with the pho-tochromic reaction.
Photochromic compounds have attracted much attention because of their potential ability for photonics devices,such as optical memory media and photo-optical switches.1–4Among various types of photochromic compounds,diarylethene deriva-tives are the most promising compounds for the application be-cause of their thermally irreversible and fatigue resistant photo-chromic performance.5,6U
pon irradiation with UV light the open-ring form isomer converts to the closed-ring one,which has a well-separated absorption band in the visible wavelength region.
Although many diarylethene derivatives have been report-ed,compounds which exhibitfluorescent emission from the closed-ring isomer are very rare.7–10An example is1,2-bis(2-methyl-1-benzothiophen-3-yl)hexafluorocyclopentene deriva-tive,which gives very weakfluorescence from the closed-ring isomer.8,11Fluorescent photochromic compounds,which rever-sibly change thefluorescence intensity along with the photo-chromic reaction,are useful for optical memory media12as well asfluorescent probes.
In this study,we have prepared a diarylethene dimer1(O–O)connected with a diyne and studied the photochromic as well asfluorescent properties.1(O–O)was synthesized from1-(2-methylbenzothiophen-3-yl)-2-(2,4-dimethyl-5-trimethylsilyl-ethynylthiophen-3-yl)hexafluorocyclopentene(2)by a one-pot procedure.132was deprotected by KOH and then homo-cou-pling reaction in THF under Cu(II)catalysis gave1(O–O).Col-orless amorphous1(O–O)was obtained with86%
yield.
3
1: O-O
Figure1shows the absorption spectral change of1(O–O) (3:2Â10À5M)in hexane by photoirradiation.Upon irradiation with350-nm light an absorption band around570nm increased and reached the photostationary state.The color of the solution changed from colorless to dark-blue,in which absorption max-imum was observed at574nm.When the dark-blue solution was irradiated with visible light( >550nm),the spectrum re-turned back to the original one with retention of the isosbestic points at298,320,and374nm.
The photoirradiated sample was analyzed with high per-formance liquid chromatography(HPLC,silicagel column,Wa-kosil5SIL,eluent hexane/ethyl acetate(99:1)).When moni-tored at the isosbestic point of320nm,two peaks were observed.When the monitoring wavelength was shifted to 574nm,at which wavelength only the closed-ring isomer ab-sorbs,only one peak was observed in the HPLC chart.Diaryl-ethenes have two conformations,with two aryl rings in anti-par-allel(ap)and parallel(p)conformation.14The methyl protons of the O–O dimer showed simple ten signals.14The ratio of con-formers were ap-ap:ap-p:p-p=1:2:1.The spectrum of the iso-lated colored dimer showed complex seven signals,as shown in Figure2.15In the NMR spectrum there existed a characteristic signal at1.98ppm assigned to one of the methyl protons of the open-ring form and characteristic signals2.04ppm assigned to two methyl protons of the closed-ring form.The ratio of the two signals was1:2,which indicates that the colored isomer is an O–C dimer having both open-ring form O and closed-ring form C.The colored isomer was identified as O–C by1H NMR. The isomer in which both diarylethenes are in the closed-ring form(C–C)was not detected.Even after prolonged irradiation any other photoproduct was not discerned.The absence of the isomer having two closed-ring form isomer in the
photoirradiat-Figure1.Absorption spectral change of1in hexane (3:2Â10À5M)by photoirradiation:O–O(solid line),1in the photostationary state under irradiation with350-nm light (dotted line),and O–C(broken line).
CopyrightÓ2003The Chemical Society of Japan
ed dimer agrees to the results observed in other dimers so far reported.16,17Excited energy transfer from the open-to the closed-ring isomers is considered to prohibit the formation of C–C dimer.The cyclization quantum yield of the dimer was measured to be 0.36.The conversion of the dimer to 1(O–C)in the photostationary state reached 0.88.
Figure 3shows the fluorescence spectra of dimer 1(O–O and O–C)and 2(R =Si(CH 3)3)in hexane by irradiation with 313-nm light at room temperature.Although 2a gives fluores-cence at 410nm,any fluorescence was not observed from 1(O–O)by excitation at 313nm.Upon irradiation with 313-nm light both 2a and 1(O–O)converted to the closed-ring isomers,2b and 1(O–C).The closed-ring isomers 1(O–C)gave red fluo-rescence at 720nm by excitation at 574nm,while any fluores-cence was not detected from 2b .The excitation spectrum of the red fluorescence agreed to the absorption spectrum of 1(O–C).
This result indicates that the fluorescence at 720nm is due to the closed-ring isomer 1(O–C).The fluorescence intensity changed upon alternate irradiation with UV and visible light.The fluo-rescence spectral change of the red fluorescence observed at longer wavelength can be potentially applicable to fluores-cence-readout optical memory.18
The present work was supported by Grant-in-Aids for Sci-entific Research on Priority Areas (Optomechatronics for Gen-erating Nanostructures,12131211).
References and Notes
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8M.-S.Kim,T.Kawai,and M.Irie,Chem.Lett.,2001,702.9T.Kawai,M.-S.Kim,T.Sasaki,and M.Irie,Opt.Mater.,
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11T.Utsumi,T.Kawai,M.Hamaguchi,K.Yoshino,and M.
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13M.Takeshita,C.Choi,and M.Irie,J.Chem.Soc.,Chem.
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14Selected data for 1(O–O):colorless amorphous;UV–vis
(hexane) max (");264(35300),290(29000),298(29000),324(22500),347(22800),371(17200);1H NMR (400MHz,CDCl 3,TMS) 1.92(s,1.5H),1.96(s,1.5H),2.10(s,1.5H),2.13(s,1.5H),2.21(s,1.5H),2.24(s,1.5H),2.35(s,3H),2.37(s,3H),2.41(s,1.5H),2.43(s,1.5H),7.50–7.80(m,8H);MS m =z 910(M þ);Anal.Calcd C 44H 26F 12S 4:C,58.01;H,2.88%;Found.C,58.33;H,3.07%.
15Selected data for 1(O–C):blue amorphous;UV–vis (hex-ane) max (");256(29200),298(28600),350(22700),391(13200),574(15500);1H NMR (400MHz,CDCl 3,TMS) 1.98(s,1.5H),2.04–2.08(m,6H),2.13–2.18(m,4.5),2.28(s,1.5H),2.39(s,3H),2.46(s,1.5H),7.20–7.57(m,8H);FAB-HRMS Calcd C 44H 26F 12S 4:m =z 910.0726;Found.m =z 910.0707(M þ).
16A.Peters and N.R.Branda,Adv.Mater.Opt.Electron.,10,
245(2000).
17T.K aieda,S.K obatake,H.Miyasaka,M.Murakami,N.
Iwai,Y.Nagata,A.Itaya,and M.Irie,J.Am.Chem.Soc.,124,2015(2002).
18T.Tsujioka and M.Irie,Appl.Opt.,37,4419
(1998).
Figure 2.1H NMR methyl signals of the
O–C.reactive materials studies
Figure 3.Absorption spectrum of 1(O–O),fluores-cence and excitation spectra of 1(O–C)and fluores-cence spectrum of 2a in hexane at room temperature.
Published on the web (Advance View)August 18,2003;DOI 10.1246/cl.2003.848

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