1、Fluorescence Quenching and Enhancement by H-bonding Interactions in Some Nitrogen Containing FluorophoresCHANDAN TAMULY, NILOTPAL BAROOAH, MOITREE LASKAR, RUPAM J. SARMA and JUBARAJ B. BARUAH*Department of Chemistry, Indian Institute of Technology, Guwahati 781 039, India(Received 26 October 2005, 9
2、 March 2006; Accepted 10 March 2006)一些含氮荧光团由于氢键相互作用而产生的荧光猝灭和增强The benzodebenzo4,5imidazo2,1-aisoquinolin-7-one (1) shows solvent dependent fluorescence emission.The compound shows quenching of fluorescence emission on interaction with polyhydroxy compounds such as 1,3-dihydroxybenzene, 1,4-dihydroxy
3、benzene. The result on fluorescence quenching is attributed to the hydrogen bonding interactions. Similar observation of fluorescence quenching by protic solvent is observed with isoindolo2,1-a perimidin-12-one (2). In the case of 2-(2-amino-phenyl)-isoindole-1,3-dione (3) enhancement of fluorescenc
4、e emission in methanol solution is observed over benzene solution. This is explained on the basis ofintermolecular hydrogen bonding. The crystal structure of adduct of 1 with 1,3-dihydroxybenzene, 1,4-dihydroxybenzene respectively and 3 are reported.Keywords: Fluorescence; Quenching; H-bonding; Solv
5、atochromicity苯并二 苯并 4,5 咪唑 2,1 - 异喹啉 - 7 -酮表明溶剂依赖荧光发射。这个化合物表明在与多羟基化合物反应的荧光发射的猝灭如 1,3 -苯二酚， 1,4 苯二酚，结果表明荧光猝灭是由于氢键相互作用。类似的观察荧光猝灭是由质子溶剂观察 isoindolo2,1-a perimidin-12-one (2).如 2-(2-amino-phenyl)-isoindole-1,3-dione (3)在甲醇溶液中加强荧光发射是在苯溶液观察的。这个解释是建立在分子间氢键的基础上。1 分别与 1,3 -苯二酚，1,4 苯二酚的加成化合物和 3 的晶体结构是有报道的。INT
6、RODUCTIONThere is a definite need for understanding enhancement or quenching of fluorescence emission of a fluorophore by externally added substrate/s 1,2.Extensive literature is available on the fluorescence properties of naphthalimide derivatives 39.Several such studies are devoted to identify on
7、and off fluorescence states in these derivatives 1013.However, there are limited studies on understandingfixed geometry responsible for quenching orenhancement of fluorescence emission. This is predominantly because of the fact that such studiesare generally performed in solution. In solution themol
8、ecules are relatively loosely bound, and thismakes it difficult to explicitly demonstrate all theweak interactions such as pp or hydrogen bondinginteractions 14. On the other hand in solid state thedifficulty is to identify an organized state that wouldserve as a model. Recently, it is pointed out t
9、hat insolution pp interaction between aromatic ringsleads to enhancing of electroniccommunicationbetween the two subsystems and such effect isreflected in fluorescence emission of the interactingsystem 15,16. Moreover, the naphthalimide derivatives have biological importance and in analogous molecul
10、es it was reported that pp interactions play a decisive role in fluorescence emission 16. We felt that if suitable motifs are identified and their properties in solid state are studied, it will add real value in determining motifs responsible for fluorescence quenching or enhancement. Thus, we have
11、studied the fluorescence properties of a few substrates (17; Fig. 1) with an aim to understand the role of hydrogen bonding in fluorescence emission in these compounds.引言：对于通过在外表上添加底物来理解增强和猝灭荧光团的荧光发射是有明确的需要1,2。有大量的文献是关于萘衍生物的荧光性39。一些此类研究都致力于识别这些衍生物的荧光或非荧光集团。但是，有限的研究都认为荧光的增强和猝灭都是由于固定的空间结构。这主要是因为这一事实，即
12、这类研究通常表现在溶液中。在溶液中的分子受着相对松散的约束，因此，很难明确地表明所有弱相互作用等如 或氢键 。另一方面在固态物质中很难一个典型的组织集团。最近，有人指出，在溶液中芳香环之间的 相互作用导致两个子系统之间电子效应增强并且这种效应反映了荧光发射的相互作用系统 15,16。此外，萘衍生物具有生物重要性和类似分子性说明它对荧光发射发挥决定性的作用 16 。我们觉得如果合适的主题被确定并且固态性质被研究，这将增加我们决定课题对于荧光淬火或加强真正价值。因此我们已经研究了一些底物的荧光性质(17; Fig. 1)，目的是了解氢键在这些化合物的荧光发射方面的作用。RESULTS AND DI
13、SCUSSIONIt is observed that the position and intensity of fluorescence emission (lex 450 nm) of benzode -benzo4,5imidazo2,1-aisoquinolin-7-one (1) issolvent dependent. The fluorescence properties ofthis compound were reported earlier 17 but theeffect of hydrogen bonding on fluorescence emissionwas n
14、ot studied. The compound 1 on excitation at450nm in methanol shows emission at 507nmwhereas it shows emission at 485nm in benzene(Fig. 2). When the intensity of fluorescence emissionof samples with identical concentrations of 1 inmethanol is compared with a solution of benzene it is found that there
15、 is a considerable amount of reduction in intensity of emission in methanol over a benzene solution. Thus, a protic solvent reduces the intensity of fluorescence emission of 1 and also takes emission towards a higher wavelength. To establish this fact we have prepared two hydrogen bonded adduct of 1
16、, namely 4 with 1,3-dihydroxybenzeneand 5 with 1,4-dihydroxybenzene and determined the crystal structures of these two adducts. The benzode benzo4,5Imidazo2,1-aisoquinolin-7-one(1) forms 2:1 adducts 4 with 1,3-dihydroxybenzeneand 5 with 1,4-dihydroxybenzene respectively (Fig.1). The structure of the
17、 adduct 4 has severalinteresting features. In the adduct 4 the H-bondingtakes place between two nitrogen atoms of twomolecules of 1 with the hydroxy groups of onemolecule of 1,3-dihydroxybenzene to form a Ushapedstructure (Fig. 3a). The adduct is formed byweak hydrogen bonding interaction between th
18、enitrogen atom and the hydroxyl groups. For theN HZO interaction the donoracceptor bonddistance and bond angles participating in hydrogenbonding in this adduct are 2.884A and 173.968respectively. The N H and HZO distances are1.958A and 0.93A , respectively. In the crystal latticethese interactions a
19、llow two molecules of 1 to appearabove each other as stacks (Fig. 3b). In this orderlyarrangement the hinges are provided by 1,3-dihydroxybenzenes. From the top view it can beseen that the molecular arrangement in the lattice issymmetric to a 908 rotation followed by a translationif each pair is con
20、sidered to be an object to be rotated.There are two types of p-separations between thearomatic rings in the crystal lattice of the adduct 4.The two separations between the aromatic layers areshown in the packing of the crystal lattice as X and Y(Fig. 3b) are 3.581A and 3.621A . These distances are s
21、lightly higher than the limit 3.5A that is conventionally found in molecules having pp interaction14,18,19. Thus, one can say that in this system the pp interaction has lesser significance.Similarly, the adduct 5 formed by benzode benzo4,5imidazo2,1-aisoquinolin-7-one with 1,4-dihyroxybenzenehas the
22、 nitrogen atom of the benzode benzo2,1-aisoquinolin-7-one bound to a hydroxylgroup of 1,4-dihydroxybenzene. The other hydroxylgroup of 1,4-dihydroxybenzene holds another nitrogenatomof benzode benzo4,5imidazo2,1-aisoquinolin-7-one. In the N HZO interactions the dDAbond distance and , DZH A angle is
23、2.884A and75.758, respectively (Fig. 4).结果与讨论观察发现苯并二苯并 4,5 咪唑 2,1 - 异喹啉 - 7 -酮荧光发射( ex=450nm)的位置和强度由溶剂决定。关于这种化合物的荧光性质报道更早 17 但是， 氢键作用的荧光发射没有研究。这种化合物在甲醇450nm 处激发说明在507nm 处发射，而在苯中则是在485nm（见图2 ） 。当强度的荧光发射相同样品相同浓度的化合物1 ，甲醇与苯相比，在甲醇中有相当数量发射强度降低。因此质子溶剂降低了化合物1的荧光发射强度也将发射的波长增长。为了说明这一事实我们准备了两个化合物1的氢键加合物，即4 ，1
24、,3 -苯二酚和5，1,4 -苯二酚，并测定这两个加合物的晶体结构。苯并二苯并 4,5 咪唑 2,1 - 异喹啉 - 7 -酮的形式2 ：1 加合物 4 与1,3 -苯二酚和5与1,4 -苯二酚分别（图1 ） 。加合物4的结构有几个有趣的特征。在加合物4中氢键是由1中带氢氧根的两个分子的两个氮原子中形成的，在1,3 -苯二酚，形成 U 型结构（图3A ） 。加合物在氮原子和羟基碱形成弱氢键作用。对于 N HO 共价键的距离和角度都对加合物氢键形成有影响（分别为2.884A and 173.96） 。N H 和 HO 键的距离分别为1.958A 和0.93A 。在晶格中这些相互作用使得1的两分子
25、表现出互相堆砌的样子。在这种有序安排取决于所提供的1,3 - 苯二酚。从上方的看法，可以看到分子安排在格中对称90旋转之后，如果每对转化被认为是一个物体旋转。芳香族环晶格的加合物4间有两种 分离的类型。这两个分离的芳香层表现在包装晶格的 X 和 Y （图3B ）是3.581A 和3.621A 。这些距离略高于平常 键3.5A 的距离 14,18,19 。因此可以说在这个系统中 作用具有较少的意义。同样，所形成的加合物5是由苯并二 苯并 4,5 咪唑 2,1 - 异喹啉 - 7 -酮与1,4 - 苯二酚形成的，苯并二苯并 4,5 咪唑 2,1 - 异喹啉 - 7 -酮的氮原子与1,4 - 苯二酚
26、的羟基集团成键。1,4 - 苯二酚的另一个羟基集团与苯并 二 苯并 4,5 咪唑 2,1 - 异喹啉 - 7 -酮的另一个氮原子相连。在 N HO 作用中 dDA 的距离和 D HA 的夹角分别为2.884A 和75.758 ，分别为（图 4 ） 。The fluorescence emission spectra of the compounds 1, 4 and 5 in solid state were measured by exciting at 450 nm. In the solid state the parent compound 1 on excitation at 450
27、nm has a fluorescence emission at 493nm with a shoulder at 550 nm. Whereas, the adduct 4 has a very feeble fluorescence emission at 530nm (Fig. 5) (lex 450 nm). The adduct 5 also shows a very weak fluorescence emission at 535nm on excitation at 450 nm. From crystallographic study it is evident that
28、there are no pp interactions among the parent fluorophores. So, it may be suggested that by formation of H-bonded adducts, the inter-motif interactions that would have originally been present in the fluorophore are changed. This results in the modification of the energy states, which lowers thefluor
29、escence intensity.We also examined the concentration dependent 1HNMR spectra of the compound 1 in acetonitrile (please refer to supplementary material). No significant changes in the chemical shifts or coupling pattern of the 1HNMR signals on change of concentration except broadening of the signals
30、due to dipolar interactions was observed. This indicates no significant pp interactions among the molecules of 1 in solution also. Alternately,acetonitrile does not change the electronic environment of the molecule 1, and this result also adds to the fact that it does not quench fluorescence of 1 bu
31、t behaves in a manner similar to that of benzene.The compound isoindolo2,1-a perimidin-12-one (2) is a structural isomer of 1 but has a differentheterocyclic ring due to a difference in the position ofthe nitrogen atoms and carbonyl groups in the ring.The fluorescence emission of 2 on excitation at
32、540nm is sensitive to solvent. For example, in methanol it shows poor fluorescence emission (Fig. 6)whereas, a solution of 2 in benzene (identicalconcentration) shows emission at 592 nm, which isabout 12-fold higher in intensity than that ofmethanolic solution. The emission of an acetonitrilesolutio
33、n has an intermediate effect on the intensity ofemission. Thus, the solvent capable of H-bonding such as methanol reduces the intensity of emissiondrastically. To check the possibility of identifying thetype of interactions among the molecules of 2 indifferent solvents the concentration dependent UV
34、visible spectra were recorded in three differentsolvents namely benzene, methanol and acetonitrile.It was found that the slopes and trends of variation ofconcentration versus absorbance are different foreach solvent. This suggests that the intermolecularsolute solvent interactions causes changes in
35、thespectra and such effects are well documented inthe literature 20. In case of a protic solvent the hydrogen bonded structure changes the originalintermotif interactions and one can see the quenchingof fluorescence due to modification of the ground state.化合物1 ，4 和5 固态的荧光发射光谱经测是在 450 nm 左右处被激发。固态的初始
36、化合物1在450nm 激发，在550nm 的肩膀493nm 荧光发射。鉴于加合物4具有非常虚弱荧光发射在530nm（图 5 ）( ex=450nm).加合物5还在535nm 显示了非常弱荧光发射在 450nm 出激发。从晶体学研究很显然，在母体荧光团间并没有 作用。因此，可以认为，由形成的 H 键加合物，跨序的相互作用，将原来本在荧光的变化。这样的结果使得降低荧光强度的能量集团得到校正。我们还研究了化合物1在乙腈中不同浓度的核磁共振光谱（请参阅补充材料） 。在化学变化中没有重大变化和耦合模式的核磁共振信号由于偶极作用除扩大信号外还改变浓度的说法。这表明在化合物1在溶液中分子间也没有显著的 作用
37、，另外，乙腈不会改变分子1电子环境的 ，这一结果也使它不猝灭荧光，但表现的方式类似苯成为事实。化合物 isoindolo 2,1 - perimidin - 12 - 1 （ 2 ）是一个结构性的异构体 1 ，但具有不同的杂环由于不同的位置，氮原子和羰基在环内。化合物2的荧光发射激发540nm 且对溶剂敏感。例如，在甲醇这表明弱荧光发射（图6 ）而化合物2在苯（相同浓度）显示发射在592nm，这是约 12倍的强度比甲醇的溶液。乙腈溶液的发射对发射的强度起媒介作用。因此溶液形成氢键的能力如甲醇大大降低了发射强度。检查的可能性，确定类型之间的相互作用的分子2在不同溶剂中的浓度依赖性紫外可见光谱记录
38、了三种不同的溶剂即苯，甲醇，乙腈。结果发现，每个溶剂斜坡和趋势的变化，浓度与吸光度不同。这表明，分子间溶质溶剂的相互作用造成的光谱变化，而这种影响是有据可查的文献 20 。如果质子溶剂的氢键结构改变了原始的相互作用和看到的荧光猝灭是由于修改的基态。To further strengthen our observations, we studiedanother related molecule 2-(2-aminophenyl)-isoindole-1,3-dione (3) that has a phthalimide ring as wellas an amino group. The p
39、osition of the amino groupallows it to have conjugation over the two rings. Theprotonation of the amino group of this moleculeaffects the intermolecular hydrogen bonding. Westudied the visible spectroscopic and fluorescenceemission spectra of this compound (3) in differentsolvents. It was found that
40、 the compound hasdifferent trends in the concentration dependentprofiles (Figs. 7 and 8) in the UV-spectra in differentabsorption intensity and shifts the absorption to ahigher wavelength. The concentration dependentUV-spectra shows that in methanol the concentrationversus absorbance has a regular g
41、rowth as expectedfrom Beers Lambert law (Fig. 7, inset) but in the caseof benzene as a solvent there is deviation from thestraight line that would pass through the origin (Fig.8, inset). This may be due to the fact that a proticmedium disrupts the intermolecular hydrogenbonding among the individual
42、molecules whereasbenzene being a non-protic solvent allows intermolecularhydrogen bonding between the moleculesof 2-(2-aminophenyl)-isoindole-1,3-dione. The effectis reflected in the fluorescence emission spectra of thecompound (3) in different solvents (lex 435 nm)also. In methanol the compound sho
43、ws emission at505 nm, in acetonitrile it emits at 487 nm, whereas itemits at 471nm in benzene (Fig. 9). The observedintensity of emission in different solvents are in the order methanol . acetonitrile . benzene. Thisindicates that the solvent polarity as well ashydrogen bonding may be responsible fo
44、r such aprocess. Methanol forms hydrogen bonds with the amino group, thus changing the magnitude of intermotif interactions. To distinguish the effect of protonation from H-bonding interactions, we recorded the visible spectra of 3 in the presence ofhydrochloric acid in methanol. The addition of aci
45、d to the methanolic solution of the compoundimmediately showed a new absorption peak at456nm with an intensity comparable to the absorption of the parent compound. The effect of addition of acid is also reflected in the fluorescence emission.On excitation of an acidic solution of 3 in methanol at 45
46、0 nm it showed altogether a new but very low intensity emission at 572 nm. These results clearly indicates that protonation of the amine quenches the emission in the case of 3. However, the observation on enhancement of intensity of fluorescence by methanol in the parent compound shows that the role
47、 of an acid and a protic solvent are totally independent. It may be concluded that hydrogenbondingwith the ZNH2 group with methanol causes disruption of intermolecular hydrogen bonding incompound 3 but does not generate a protic state. The structure of the molecule 3 in solid state hasintermolecular
48、 hydrogen bonding between ZNH2groups with the carbonyl group of other molecules.The IR spectra in solid state clearly suggest the presence of intermolecular hydrogen bonding. In theIR spectra of 3 two very sharp absorptions at3462 cm21 and 3385 cm21 due to intermolecular hydrogen bonding are observe
49、d. The effect can beexplained by the scheme shown in Fig. 10a.Methanol being a protic solvent cause disruption ofsuch hydrogen bonding and this leads to fluorescenceenhancement. This suggests that the intermolecular hydrogen bonding among 3 is favoured inthe case of benzene. The disruption of H-bondingmakes the nitrogen atom more electron rich to
