渠星宇 陳 偉 石茂虎 沈 珍＊,

(1南京大學化學化工學院，配位化學國家重點實驗室，南京210093)

(2晉中學院化學化工學院，晉中030600)

基于硼-二吡咯亞甲基二聚體的紅光三價鐵離子探針的合成與性質

渠星宇1,2陳 偉1石茂虎1沈 珍＊,1

(1南京大學化學化工學院，配位化學國家重點實驗室，南京210093)

(2晉中學院化學化工學院，晉中030600)

在硼-二吡咯亞甲基(BOIDPY)的β-β(2/6)位偶聯(lián)得到一種新型的紅光二聚體BODIPY熒光探針1，該探針可以發(fā)生高效的能量轉移，假-斯托克斯位移可以達到222 nm。探針1能夠專一性地識別三價鐵離子，不受其它常見金屬離子的干擾，可以作為檢測三價鐵離子的高選擇性的探針。

硼-二吡咯亞甲基染料；熒光探針；紅光；能量轉移；三價鐵離子

Boron-dipyrromethene(BODIPY,BODIPY core= 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)dyes have attracted increasing interests in the last decade for its remarkable photophysical properties,such as high extinctioncoefficient,highfluorescencequantum yields.Its structure can be easily modified to synthesis versatile dyes for practical applications[1],such as fluorescenceindicatorsforcations,anions,small molecules,reactiveoxygenspeciesandso on[2].However, the Stokes′shift of BODIPY is 5～20 nm and the emission wavelength around 500～560 nm limits its application in living cell imaging.To red shift the main BODIPY absorption band,several approa-ches have been explored,such as the substitution of aromatic or heteroaromatic groups at the 3-,5-and/or 1-,7-positions on the pyrrolemoieties[3],aromatic ring fusion[4],replacing the meso-carbon atom with an azaatom[5].Recently,Bard et al.[6]have reported an alternativewaytoredshiftthemainBODIPY absorption band by synthesizing the BODIPY dimersand trimers.

Ferric ion plays diverse and crucial roles in several biological processes.Particularly,ferric ion is an important element in enzymes,proteins,etc.The abnormal quantity of ferric ions may cause lots of disease and damage human health[7],including hepatites,cancer,etc.Owing to simplicity and high sensitivity,fluorescence is a powerful method to probe ions.Lots of highly selective and sensitive rhodaminebased chemosensors have been exploited for the detection of Fe3+ion[8].However,only a few BODIPY-based probes for Fe3+have been reported[9].Recently we have reported a BODIPY derivative with 5-(quinolin-2-yl)thiophen-2-yl(TQ)substituted at mesophenyl position that exhibits specific response to Fe3+[9b]. Herein,we extend this research by oxidative coupling BODIPY at the β-β(2/6)positions so that its absorbance and fluorescence bands are red shifted to the red region.The Fe3+-detection properties have been investigated by fluorescence titration spectroscopy.

1 Experimental

1.1 Reagents and instruments

Unless otherwise noted,all reagents or solvents were analytical reagents obtained from commercial suppliers and used without further purification.All air and moisture sensitive reactions were carried out under an argon atmosphere.Dry CH2Cl2was obtained by refluxing and distilling over CaH2under nitrogen. Triethylamine was obtained by simple distillation.

The1H NMR and13C NMR spectroscopic measurements were performed at 500 MHz(DRX-500),and 125 MHz(DRX-500),respectively on a Bruker 500 MHz spectrometer.Mass spectra were obtained with a Bruker Daltonics Autoflex IITMMALDI TOF MS spectrometer.Fluorescencespectralmeasurements werecarriedoutbyusingaHitachiF-4600 fluorescence spectrophotometer.Electronic absorption spectra were recorded with a Shimadzu UV-2550 spectrophotometer.

1.2 Procedures for metal ion sensing

Stock solutions of all sorts of metal ions(0.1 mol·L-1),such as Zn2+,Cu2+,Co2+,Fe3+,Ni2+,Hg2+, were prepared in deionized water.A stock solution of 1(10 μmol·L-1)was prepared in DMSO.In titration experiments,each time a 3 mL solution of 1(10 μmol ·L-1)was filled in a quartz optical cell of 1 cm optical path length,and the Fe3+stock solution was added into the quartz optical cell gradually by using a micropipet.In selectivity experiments,the test samples were prepared by adding appropriate amounts of metal ion stock solution into 3 mL solution of 1(10 μmol·L-1). During fluorescence measurements of 1,the excitation wavelength was 334 nm(for exciting the 2-(thiophen-2-yl)quinoline moiety)or 495 nm(for exciting BODIPY fluorophore)with the excitation slit of 5 nm and the emission slit of 10 nm.The emission spectra area of the measured compound 1 was obtained between 350～650 nm.

1.3 Synthesis of BODIPY dimer 1

Scheme 1Synthetic procedure for the preparation of BODIPY dimer 1

The synthesis of BODIPY dimer 1 is outlined in Scheme 1.The starting material 3 was prepared according to a published procedure(yield 45%)[9b]. The BODIPY monomer 2 was prepared through the trifluoroacetic acid catalyzed condensation reaction of 5-(quinolin-2-yl)thiophene-2-carbaldehydewith2,4-dimethyl-pyrrole in 60%yield[9b].The target BODIPY dimer 1 was produced by the self coupling reaction of2 according to the following procedure:2(0.22 mmol, 100 mg)and FeCl3(0.55 mmol,152 mg)were mixed in 30 mL CH2Cl2.The mixture was stirred for 30 min atambienttemperature.Thenthereactionwas quenched with CH3OH and washed with water,dried over anhydrous sodium sulfate,and concentrated at reduced pressure.The crude products were purified by silica-gel column chromatography using CH2Cl2as the eluent to afford the red powder 1.Yield:9.9%,1H NMR(CDCl3,500 MHz):8.17(d,J=15 Hz,2H),8.06 (d,J=15 Hz,2H),7.84～7.71(m,8H),7.53(t,J=10 Hz,2H),7.06(m,2H),6.04(d,J=10 Hz,2H),5.69(s, 1H),4.08(s,2H),2.57(s,9H),1.76(d,12H);13C NMR(CDCl3,125 MHz):157.3,156.8,156.3,156.1, 151.5,148.1,147.8,144.3,143.4,143.2,140.1, 137.9,137.5,136.8,134.3,133.4,132.7,132.2, 131.9,130.1,129.3,129.1,128.9,127.5,127.4, 126.7,126.4,125.7,122.0,121.5,119.9,117.2,29.7, 23.3,14.7,14.1,11.7.MALDI-TOF MS:m/z:912.7 (M+)

2 Results and discussion

B3LYP geometry optimizations is carried out with 6-31G(d)basis sets to determine the configuration of 1.The structure of 1 is similar to the previously reported alkyl substituted BODIPYs.Both 2-(thiophen -2-yl)quinoline moiety and the indacene plane of 1 are nearly planar,also the torsion angle between the two planes are 83.86°.The two BODIPY monomeric units of dimers 1 are not orthogonal with the torsion angle being 67.7°.

Fig.1 Geometry optimization of 1 at the B3LYP/6-31G(d) level[10]

2.1 Spectroscopic properties of 1 and 2

The UV/Vis absorption and fluorescence spectra of 1 and 2 in CH2Cl2are shown in Fig.2 .The absorption maxima of 2 is centered at approximately 514 nm, while the absorption of 1 is red shifted to 536 nm due to the formation of dimeric structure through the(2/6) positions coupling.The shoulder at 505 nm of 1 is attributed to the molecular C-C frame vibration,which is typical of BODIPY dyes.The weaker absorption band in the 300～400 nm region of 1 is attributed to the transition from 2-(thiophen-2-yl)quinoline moiety[2c]. Exciting 2-(thiophen-2-yl)quinoline moiety in compound 1 at 334 nm,both the emission band for 2-(thiophen-2-yl)quinoline(TQ)moiety at 386 nm and the emission typical for BODIPY fluorophore at 556 nm are observed.These results indicate that energy transfer partially occurs at compound 1 from TQ moiety to the BODIPY acceptor.

Fig.2 Absorption(solid line)and fluorescence(dash line) spectra of 1(10 μmol·L-1)and 2(10 μmol·L-1)in CH2Cl2solvent(λex=334 nm)

2.2 Detective property of 1

Exciting at 334 nm,the fluorescence intensity of 1 at 386 nm and 556 nm are significantly quenched upon the addition of Fe3+,since specific chelating property of the 2-(thiophen-2-yl)quinoline and the Fe3+ion[9b].The fluorescence spectrum of 1 is almost not influenced by the addition of 100 equiv.of other metal ions such as Co2+,Cu2+,Ni2+,Zn2+,and a little decreased by the addition of 100 equiv.of Hg2+,suggesting that compound 1 has high selectivity toward Fe3+(Fig.3 ).

Fig.3 Fluorescence spectra of 10 μmol·L-11 upon addition of different metal ions(100 equiv. Co2+,Cu2+,Ni2+,Zn2+,Hg2+,Fe3+)in DMSO solution

Fig.4 Top:changes in the fluorescence spectrum of 1 (10 μmol·L-1in DMSO)as a function of Fe3+concentration;Bottom:the changes of emission intensity of 1(10 μmol·L-1in DMSO)at 556 nm as a function of CFe3+/C1excited at 334 nm and 495 nm

The coordination of dimer 1 with Fe3+is investigated by spectrophotometric titration in DMSO,as shown in Fig.4 .When exciting at 334 nm,the fluorescence intensity of 1 at 386 nm and 556 nm graduallydecreaseduponadditionofincreasing amount of Fe3+(0～100 equiv.of Fe3+).However,exciting at 495 nm,the fluorescence intensity of 1 at 556 nm is almost unaffected.The results further indicate that the coordination of the 2-(thiophen-2-yl)quinoline to Fe3+inhibits the energy transfer from 2-(thiophen-2-yl) quinoline to the BODIPY,which is the main reason for the fluorescence quenching.

In summary,we have designed a red-visible BODIPY dimer containing 2-(thiophen-2-yl)quinoline substitunent at meso position which shows specific binding with Fe3+in DMSO solution.The high selectivity of 1 toward Fe3+with significant fluorescence quenching may have applications as Fe3+indicator in aqueous media.

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Synthesis and Properties of Red fluorescent Probe for Fe3+Based on Boron-Dipyrromethene Dimer

QU Xing-Yu1,2CHEN Wei1SHI Mao-Hu1SHEN Zhen＊,1
(1State Key Laboratory of Coordination Chemistry,School of Chemistry and Chemical Engineering,Nanjing University,Nanjing 210093,China)
(2College of Chemistry and Chemical Engineering,Jinzhong University,Jinzhong,Shanxi 030600,China)

A red fluorescence boron-dipyrromethene(BODIPY,BODIPY core=4,4-difluoro-4-bora-3a,4a-diaza-sindacene)dimer 1,which is linked through β-β(2/6)position from a coupling reaction,exhibits efficient energy transfer with 222 nm pseudo Stokes′shift.The BODIPY dimer 1 shows high selectivity and sensitivity towards Fewhen the ion co-exsists with common interfering metal ions and it may be used as an indicator for Fe3+.

Boron-dipyrromethene(BODIPY)dyes;fluorescent sensor;red visible;energy transfer;Fe3+

A

1001-4861(2015)03-0580-05

10.11862/CJIC.2015.072

2014-10-06。收修改稿日期：2014-12-12。

國家自然科學基金(No．21371090)資助項目。

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