Influence of cation size on the fluorescent properties of bis-coronand biphenyl-derived complexes Ana M Costero To cite this version: Ana M Costero. Influence of cation size on the fluorescent properties of bis-coronand biphenyl-derived complexes. Supramolecular Chemistry, Taylor & Francis: STM, Behavioural Science and Public Health Titles, 2007, 19 (03), pp.151-158. 10.1080/10610270600915300. hal-00513486 HAL Id: hal-00513486 https://hal.archives-ouvertes.fr/hal-00513486 Submitted on 1 Sep 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Supramolecular Chemistry For Peer Review Only Influence of cation size on the fluorescent properties of bis- coronand biphenyl-derived complexes Journal: Supramolecular Chemistry Manuscript ID: GSCH-2006-0041.R1 Manuscript Type: Full Paper Date Submitted by the 11-Jul-2006 Author: Complete List of Authors: Costero, Ana; University of Valencia, Organic Chemistry Keywords: Sensor, Biphenyl, Fluorescence, Conformational chage Note: The following files were submitted by the author for peer review, but cannot be converted to PDF. You must view these files (e.g. movies) online. Figure 7.cdx Chart1.cdx Figure 4.cdx URL: http:/mc.manuscriptcentral.com/tandf/gsch Email: [email protected] Page 1 of 20 Supramolecular Chemistry 1 2 3 4 Influence of cation size on the fluorescent properties of bis-coronand 5 biphenyl-derived complexes 6 7 8 Ana M. Costero *, Joaquín Sanchis, Salvador Gil, Vicente Sanz. 9 10 11 Departament de Química Orgánica, Universitat de València, C/ Dr. Moliner 50, 46100 12 Burjassot, Spain. 13 14 15 16 For Peer ReviewAbstract Only 17 18 A new bis-coronand derived from biphenyl has been prepared and its complexing and 19 sensing properties for alkaline, alkaline-earth and transition cations have been studied. 20 Open and clamp complexes are formed depending on the cation size and complex 21 stoichiometry. Both types of geometries can be distinguished due to their different 22 2+ 23 fluorescent behavior. Zn gives rise to 1:1 and 1:2 complexes with a similar geometry. 24 25 Introduction 26 27 28 Molecular systems that combine binding ability and photochemical or 29 1 30 photophysical properties are of great interest for designing chemosensors. It has 31 recently been established that conformational restriction is a viable mechanism for 32 2 33 transducing ion binding into enhanced fluorescence emission in organic fluorophores. 34 35 Thus, biphenyl and bipyridyl derivatives which experiment fluorescence enhancement 36 3 37 after complexation have been described in the literature. However, studies carried out 38 by Benniston et al. have demonstrated that fluorescence quantum yields for byphenyl 39 40 polyethers are dependent on the torsion angle around the biphenyl group. Planar 41 4 42 geometries favour higher yields and longer lifetimes. For all these reasons, we have 43 44 been interested in using the 4,4’-bis(N,N-dimethylamino)biphenyl (TMB, 45 46 tetramethylbenzidine) subunit in the design and synthesis of red-ox and fluorescent 5 47 sensors. TMB-derivatives ligands show very peculiar fluorescent properties. Firstly, the 48 49 presence of additional amino groups in substituents bound to the aromatic rings does not 50 51 give rise to a quenching of the fluorescence whatever the spacer present. Normally, 52 53 amines transfer one electron to the photoproduced vacancy in the HOMO of the 54 fluorophore which quenches fluorescence. In these compounds, however, the 55 56 diaminobiphenyl fluorophore has a rather high energy HOMO (owing to its easy 57 58 oxidabizability), so PET from the amino is not probable. Secondly, an increment in the 59 60 rigidity of these fluorophores makes them less fluorescent. URL: http:/mc.manuscriptcentral.com/tandf/gsch Email: [email protected] Supramolecular Chemistry Page 2 of 20 1 2 3 We now report the sensing behaviour of a new ligand that contains benzylamino 4 5 coronands as binding units in order to study the influence that the size of different 6 7 cations has in the fluorescent behaviour of the ligand. The most important difference 8 9 would be related to the formation of open-like complexes of clamp-like complexes since 10 the type of complexation is closely related to the dihedral angle between both aromatic 11 12 rings and consequently to the fluorescent properties of the photo physical moiety. 13 14 NMe2 NMe2 15 O O 16 For Peer Review Only 17 N O O O N 18 X 19 X O O O N 20 N 21 1 X=CO 3 22 O O NMe 2 X=CH2 23 2 NMe2 24 Chart 1 25 26 27 28 Photophysical characteristics of 2 and effect of protonation. Photophysical 29 30 properties of 2 in CH 3CN were studied (table 1). As expected, they are not so different 31 6b 32 from those observed for the related compounds previously described. Emission of 33 fluorescence in 2 is remarkably blue-shifted in comparison to TMB , and is even more 34 35 so when compared with its carbonylic counterpart 1 (Figure 1). By contrast, 2 shows a 36 37 similar behaviour to that observed for control compound 3. 38 39 40 Table 1: Data for absorption in the UV and emission of fluorescence for the ligands in CH 3CN 41 Ligand Absortion λλλ (nm) Emission λλλ (nm) Quantum Yield ( φφφ) 42 max max (εεε cm -1M-1) 43 TMB 310 (34668) 401 0.13 44 1 295 (29600) 474 0.08 45 2 270 (42135) 363 0.057 46 3 269 (27781) 360 0.061 47 48 49 50 51 52 53 54 55 56 57 58 59 60 * Fax: 34 963543152; Tel: 34 96 354 4410; [email protected] URL: http:/mc.manuscriptcentral.com/tandf/gsch Email: [email protected] Page 3 of 20 Supramolecular Chemistry 1 2 3 4 2 5 80E+05 TMB 6 1 7 3 8 60E+05 9 10 11 40E+05 12 13 cps 14 20E+05 15 16 For Peer Review Only 17 0 18 19 350 400 450 500 550 600 650 700 20 wavelenght (nm) 21 22 Figure 1. TMB 1 2 3 λ λ 23 Fluorescence Spectra for , , and in CH 3CN at 20ºC. exc = 310 nm, exc = 300 nm, 24 λexc = 300 nm and λexc = 340 nm respectively. 25 26 This behaviour is in agreement with the hypothesis of an excited state, in which both 27 28 biphenyls rings are coplanar and destabilised by the presence of substituents. Thus, S 1 is 29 30 unfavoured by sterical repulsions and then, the energetic difference S 1→S0 is enhanced 31 in comparison with TMB . On the other hand, in the presence of a weak acid such as 32 33 citric acid, a quenching of fluorescence was obtained (Figure 2). Protonation of the 34 35 azacrown nitrogen by the citric acid would induce the formation of an intramolecular 36 37 hydrogen bond with the nitrogen in the opposite crown, forcing the dihedral angle in the 38 39 biphenyl far from the coplanarity, which induces a quenching of the fluorescence. After 40 addition of TFAA, the arylic nitrogens are also protonated, and then emission of 41 42 fluorescence in 2 is strongly blue-shifted just as TMB is in the same acidic conditions. 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 URL: http:/mc.manuscriptcentral.com/tandf/gsch Email: [email protected] Supramolecular Chemistry Page 4 of 20 1 2 3 4 5 80E+05 6 7 2 8 60E+05 9 10 11 cps 40E+05 12 13 2+ Cítric acid 14 15 20E+05 16 For Peer Review Only 17 2 + TFAA 18 0 19 320 340 360 380 400 420 440 460 480 500 20 wavelenght (nm) 21 22 23 Figure 2. Fluorescence spectrum of 2 under different acid-base conditions in CH 3CN at 20 ºC, λ exc = -6 24 300 nm and initial concentration of ligand of 2.30 x 10 M in CH 3CN. 2: ligand in CH 3CN or in 2.63 x -5 -6 25 10 M of tetramethylamonnium hydroxide in CH 3CN. 2+Cítric acid : ligand in 9.54 x 10 M of citric 26 acid in CH 3CN. 2 + TFAA: ligand in a great excess of trifluoroacetic acid in CH 3CN. 27 28 29 Complexation studies with alkaline cations. 30 + + + + 31 Titrations of 2 with perchlorates of Na , K , Cs and Li were performed in CH 3CN. 32 + 7 33 Data of the titration with Na were fitted by SPECFIT to a 1:1 + 1:2 (L:M) 34 35 stoichiometry model, where the complexation constants were log K 1 = 5.2 ± 0.7 and log 36 K2 = 11.5 ± 0.2. The theoretical spectra modelisation of the complexes (see 37 38 suplementary material Fig. 9 and 10) suggested that the 1:1 complex would exhibit a 39 40 lower quantum yield than 2, while it should be higher for LM 2 than for the free ligand 41 42 which was the experimentally observed behaviour (Figure 3a). According to our 43 previously reported results, 6 a 1:1 clamp-type complex was proposed in which a more 44 45 constrained angle in the biphenyl moiety would be translated in a quenching of the 46 47 fluorescence.