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8Calixarenes Каликсарены
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Paper Статья
DOI: 10.6060/mhc160533k
The Upper Rim Functionalized Calixarene Ketocyanines: synthesis, structure and fluorescence Properties
Yuriy Matvieiev,a Andrii Kulinich,a Aleksey Ryabitskii,a Svitlana Shishkina,b Oleg Shishkin,b Vasyl Pivovarenko,c and Vitaly Kalchenkoa@
institute of Organic Chemistry, National Academy of Sciences of Ukraine, 02660 Kyiv, Ukraine bInstitute for Single Crystals, National Academy of Sciences of Ukraine, 61001 Kharkiv, Ukraine cChemical Faculty, Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine @Corresponding author E-mail: [email protected]
The calix[4]arene ketocyanine receptors bearing nitro-, amino- or urea moiety at the wide macrocycle rim were elaborated. Their molecular structures, UV-Vis absorption and fluorescence properties were studied. The estimated solvatofluorochromism levels and quantum yield values demonstrate clearly a possibility of control of the fluorescence colour and intensity by varying the nature of the analyte bound in the proximity of the fluorophore ketocyanine unit.
Keywords: Calix[4]arene, ketocyanine, Knoevenagel reaction, X-ray diffraction study, solvatochromism.
функционализированные по верхнему ободу каликсарен-кетоцианины: синтез, структура и флуоресцентные свойства
Ю. Матвеев^ А. Кулинич^ A. Рябицкий^ С. Шишкина^ О. Шишкин^ В. Пивоваренко^ В. Кальченко^
Институт органической химии НАН Украины, 02660 Киев, Украина ъИнститут монокристаллов НАН Украины, 61001 Харьков, Украина
cХимический факультет Киевского национального университета им. Тараса Шевченко, 01601 Киев, Украина @E-mail: [email protected]
Реакцией Кновенагеля легкодоступного нитроформилдипропоксикаликс[4]арена с а,в-ненасыщенными циклопентанонами в среде ионной жидкости диметиламмонийдиметилкарбамата получены каликс[4]арен-кетоцианины, содержащие нитро-, амино- или мочевинную группу на широком (верхнем) ободе макроцикла. Методами ЯМР спектроскопии и рентгеноструктурного анализа установлена их конусообразная структура в растворах и кристаллическом состоянии. В кристаллической фазе молекула каликс[4]арен-кетоцианина существует как центросимметричный димер, образованный за счет межмолекулярной циклизации углерод-углеродных связей кетоцианиновых фрагментов. Исследованы электронные спектры поглощения и флуоресценции полученных соединений. Объемы сольватофлуорохромии и значения квантовых выходов флуоресценции полученных соединений демонстрируют возможность контроля цвета и интенсивности их флуоресценции путем варьирования характера аналита, связанного супрамолекулярными взаимодействиями типа гость-хозяин в непосредственной близости от флуорофорного кетоцианинового фрагмента.
Ключевые слова: Каликс[4]арены, кетоцианины, реакция Кновенагеля, рештеноструктурный анализ, сольватохромия.
Introduction
Experimental
Fluorescent probes - organic molecules with an analyte receptor and fluorophore group - is a powerful tool to study the structure and function of biomolecules, cell organelles and cells in general.11"31 Therefore, design of high sensitive and selective sensors for small organic molecules is certainly a topic of great interest in modern organic chemistry. The development of ultra-sensitive detection devices has a strong impact on bioanalysis, as the sensitivity of biochemical assays could be dramatically increased.141
According to the definition approved by IUPAC "a chemical sensor is a device that transforms chemical information, ranging from the concentration of a specific sample component to total composition analysis, into an analytically useful signal". In a narrow sense, the sensor is a molecule, which is able to bind selectively the target molecule (or supra-molecular structure, living cell) and provide information about this binding. The main issue in the design of any effective chemosensor is the association of a selective molecular recognition event with a physical signal highly sensitive to its occurrence. The considerable interest to such devices is caused by relatively simple UV-Vis or fluorescence technique and their superior sensitivity.[5-8]
Calixarenes due to their distinctive tuneable cavity and its amenability to decoration, through regio- and stereoselective control, have resulted in their widespread utilization as a host molecules in supramolecular chemistry.[910] They show unique ability to recognize and selectively bind in the Host-Guest supramolecular complexes ions, organic and biomolecules[11-14] that in turn makes them promising receptors to create fluorescent probes.
In this paper, we report the synthesis as well as structural and UV-Vis-fluorescent studies of calix[4]arenes bearing ketocyanine fluorophore groups at the upper macrocycle rim and nitro group or urea fragments in distal position to the ketocyanine fluorophore moiety.
All the reactions were carried out in freshly distilled anhydrous solvents. Melting points were determined on a Boetius apparatus and are uncorrected. Column chromatography was carried out using Acros Organics silica gel (0.04-0.06 mm, pore diameter 6 nm). 'H and 13C NMR spectra were recorded on Varian GEMINI 2000 spectrometer with frequency 400 and 100 MHz, respectively (TMS as an internal standard). 'H-'H COSY spectra were acquired into 2048 (F2) and 512 (F1) time-domain data matrix. Mass-spectra were recorded on Agilent 1100 LS/MSD spectrometer. The UV/ Vis and fluorescence spectra were recorded with Shimadzu UV-3100 spectrophotometer and Solar-CM2203 spectrofluorometer (Belarus) correspondingly. All spectra were registered at 20 °C with sampling interval of 1 nm, slit width of 2 nm (the same widths for the incident beam and fluorescent light). The UV-Vis spectra were registered at concentrations 10-5-2-10-5 M in 1 cm quartz cuvettes. For fluorescent measurements these solutions were further dissolved so that their optical densities at the absorption maxima did not exceed 0.1 (to avoid inner filter effects). Solvent for spectral measurements were purified according to the methods given in [15] and not degassed.
The X-ray diffraction data were collected on an Xcalibur-3 diffractometer (graphite monochromated MoKa radiation, CCD detector). The structures were solved by direct methods using the SHELXTL package.[16] The positions of the hydrogen atoms were located from electron density difference maps and refined using the "riding" model with U. =nU for the carrier atom (n=1.5 for
° iso eq v
methyl and n=1.2 for other hydrogen atoms). The hydrogen atoms of the hydroxyl groups are refined using isotropic approximation. The final atomic coordinates, and crystallographic data have been deposited with the Cambridge Crystallographic Data Centre, 12 Union Road, CB2 1EZ, UK (fax: +44-1223-336033; e-mail: [email protected]) and are available on request quoting the deposition numbers.
Structures of molecules 1-5 are shown in Scheme 1. The synthetic procedures for 1 and 2 are described elsewhere.[17]
3a: Yield 87 %. M.p. >300 °C (dec). 'H NMR (CDCl3) 8H ppm: 1.33 (6H, t J=7.3 Hz, OCH2CH2CH,), 2.10 (4H, m, OCH2CH2CH3), 3.04 (6H, s, N(CH3)2), 3.10 (4H, br.s, CH2CH2 of cyclopentanone), 3.46 and 3.49 (4H, two overlapped d J2=13.4 Hz, Ar-CH2-eq.), 4.02 (4H, m, OCH2CH2CH3), 4.30 and 4.32 (4H, two
4a,b 5a,b r = NMe2 (a); OMe (b)
Scheme 1. Synthesis of calixarene-based ketocyanines.
overlapped d J2=13.4 Hz, Ar-CH2-ax.), 6.74 (2H, d J=8.7 Hz, ArH), 6.83 (2H, t J=7.75 Hz, ArH), 6.98 (4H, m, ArH), 7.36 (2H, s, ArH), 7.48 (1H, br.s, -CH=), 7.52 and 7.55 (3H, two overlapped br.s, 2ArH + -CH=), 8.04 (2H, s, ArH), 8.73 (1H, s, OH), 9.52 (1H, s, OH). 13C NMR (CDCl3) SC ppm: 195.72, 159.62, 151.55, 150.69, 134.88, 134.07, 132.993, 132.85, 132.81, 132.52, 131.60, 131.41, 129.50, 129.00, 128.40, 128.11, 125.60, 124.40, 112.10, 111.81, 78.62, 40.19, 31.62, 31.42, 26.79, 23.60, 11.05. LC-MS: m/z=779.4 [M]+. Found: C 76.32, H 6.54, N 3.48 %. C49H50N2O7 requires C 75.56, H 6.47, N 3.60.
The X-ray diffraction study of 5-nitro-17-{(E)-[(3E)-3-(4-dimethylaminobenzylidene)-2-oxocyclopentylidene] methyl}-26,28-dihydroxy-25,27-dipropoxycalix[4]arene, 3a (the deposition number CCDC 1025172). The colourless crystals of 3a C49H50O7N2-CHCl3 are monoclinic. At 100 K: a=22.138(1), b=10.5509(5), c=19.520(1) A, p=104.794(5)°, V=4408.3(4) A3, Mr=898.28, Z=4, space group P21/c, dcalc=1.353 g/cm3, ^ (MoKa)=0.264 mm-1, F(000)=1888. Intensities of 33690 reflections (12849 independent, Rint=0.085) were measured (ro-scaning, 2©max=60°). Full-matrix least-squares refinement of the structure against F2 in anisotropic approximation for non-hydrogen atoms using 12811 reflections converged to wR2=0.173 (R1=0.074 for 6897 reflections with F>4a(F), S=0.987).
3b: Yield 69 %. M.p. 303-306 °C. 'H NMR (CDCl3) 5H ppm: 1.32 (6H, t J=7.3 Hz, OCH2CH2CH3), 2.08 (m, 4H, OCH2CH2-CH3), 3.08 (4H, br.s, CH2CH2 of cyclopentanone), 3.47 and 3.50 (4H, two overlapped d J=13.2 Hz, Ar-CH2-eq.), 3.84 (3H, s, OCH3), 3.99 (4H, m J=6.3 Hz, OCH2CH2CH3), 4.31 and 4.32 (4H, two overlapped d J2=13.2 Hz, Ar-CH2-ax.), 6.83 (2H, t J=7.6 Hz, ArH), 6.98 (6H, m, ArH), 7.37 (2H, s, ArH), 7.52 (1H, br.s, -CH=), 7.55 and 7.57 (3H, overlapped br.s and d J=7.6 Hz, -CH= + 2ArH,), 8.04 (2H, s, ArH), 8.79 (1H, s, OH), 9.52 (1H, s, OH). 13C NMR (CDCl3) SC ppm: 195.78, 160.23, 159.58, 154.86, 151.54, 139.54, 135.32, 134.17, 133.81, 132.91, 132.76, 132.26, 131.61, 131.54, 129.44, 129.01, 128.73, 128.37, 128.19, 127.29, 125.57, 124.37, 114.17, 78.61, 55.38, 31.60, 31.40, 26.73, 26.64, 23.58, 11.03. LC-MS: m/z=766.4 [M]+. Found: C 76.02, H 6.24, N 1.88 %. C48H47NO8 requires C 75.27, H 6.19, N 1.83.
The X-ray diffraction study of 5-nitro-17-{(E)-[(3E)-3-(4-methoxybenzylidene)-2-oxocyclopentylidene]methyl}-26,28-dihydroxy-25,27-dipropoxy-calix[4]arene, 3b (CCDC 1025173). The colourless crystals of 3b 2C48H47O8№CH3OH4H2O are monoclinic. At 100 K: a=42.215(4), b=10.2820(7), c=20.249(2) A, P=99.321(9)°, V=8673(1) A3, Mr=1635.84, Z=4, space group C2/c, dcalc=1.253 g/cm3, ^ (MoKa)=0.088 mm-1, F(000)=3480. Intensities of27822 reflections (7618 independent, Rint=0.125) were measured (ro-scaning, 2©max=50°). The restriction on the C-O bond length (1.41 A) for the solvate methanol molecule was applied. Full-matrix least-squares refinement of the structure against F2 in anisotropic approximation for non-hydrogen atoms using 7579 reflections converged to wR2=0.210 (R1=0.080 for 3463 reflections with F>4a(F), S=0.927).
General method for synthesis of 5-N-(2-methoxyethyl)-N'-urea-17-{(E)-[(3E)-3-(4-dimethylamino(methoxy)benzyli-dene)-2-oxocyclo-pentylidene]methyl}-25,27-dipropoxy-26,28-dihydroxy-calix[4]arenes, 5a,b.
To a suspension of 0.5 mmol of nitrocalixarene 3a,b in 20 ml of methanol, 1.5 ml of 100 % hydrazine hydrate (30 mmol) was added. The reaction mixture was heated to 70 °C and 0.1 ml of 50% aqueous suspension of Raney nickel was added. After stirring at 70 °C for 5 hrs reaction mixture was cooled to room temperature and 15 ml of chloroform was added. The solution was filtered off through silica gel. Evaporation of solvent resulted in aminocalixarenes 4а,b as yellow solids.
To a solution of 0.4 mmol aminocalixarene 4а,b in 10 ml of chloroform 0.4 mmol of 2-methoxyethyl isocyanate in 2 ml of chloroform was added dropwise. Reaction mixture was stirred at room temperature for 12 hours. The solvent was removed under
reduced pressure and the residue - compounds 5а,b - was purified by column chromatography (eluent - ethyl acetate).
5а: Yield 68%. M.p. >320 °C (dec.). 'H NMR (CDCl3) SH ppm: 1.32 (6H, t J=7.3 Hz, OCH2CH2CH3), 2.08 (4H, m, OCH2CH2CH3), 3.04 (6H, s, N(CH3)2), 3.09 (4H, brs, CH2CH2 of cyclopentanone;), 3.32 (3H, s, OCH3), 3.38 and 3.43 (8H, two overlapped m, CH2CH2+Ar-CH2-eq.), 3.99 (4H, t J=6.1 Hz, OCH2CH2CH3), 4.31 and4.32 (4H, two overlapped d J2=12.5 Hz, Ar-CH2-ax.), 4.95 (1H, t J=5.4 Hz, NH), 6.14 (1H, s, NH), 6.73 (2H, d J=8.8 Hz, ArH), 6.78 (2H, t J=7.6 Hz, ArH), 6.95 (6H, m, ArH), 7.35 (s, 2H, ArH), 7.47 (br.s, 1H, -CH=), 7.52 and 7.54 (3H, overlapped br.s and d, -CH= +2ArH), 8.40 (1H, s, OH), 8.86 (1H, s, OH). 13C NMR (CDCl3) SC ppm: 195.98, 156.84, 154.92, 151.77, 134.78, 134.10, 133.121, 132.97, 132.59, 131.50, 129.02, 128.93, 128.60, 128.42, 127.47, 125.45, 124.48, 111.85, 78.48, 71.95, 58.72, 40.15, 31.59, 31.36, 30.96, 26.71, 23.52, 10.97. LC-MS: m/z=852.5 [M+H]+. Found: C 75.02, H 6.94, N 4.88 %. C53H59N3O7 requires C 74.89, H 7.00, N 4.94.
5b: Yield 88%. M.p. >260 °C (dec.). 'H NMR (CDCl3) SH ppm: 1.32 (6H, t J=7.3 Hz, OCH2CH2CH3), 2.07 (4H, m, OCH2CH2CH3), 3.11 (4H, br.s, CH2CH2 of cy clopentanone), 3.31 (3H, s, OCH3), 3.36 and 3.42 (8H, two overlapped m, CH2CH2 + Ar-CH2-eq.), 3.84 (3H, s, OCH3), 3.99 (t, 4H, J=6.1 Hz, OCH2CH2CH3), 4.29 and 4.32 (4H, two overlapped d J2=13.2 Hz, Ar-CH2-ax.), 5.07 (1H, t J=5.4 Hz, NHCH2), 6.36 (1H, s, ArNH), 6.76 (2H, t J=7.5 Hz, ArH), 6.95 (8H, m, ArH), 7.36 (2H, s, ArH), 7.52 (1H, br.s, -CH=), 7.54 and 7.56 (3H, overlapped br.s and d, -CH=+2ArH), 8.36 (1H, s, OH), 8.91 (1H, s, OH). 13C NMR (CDCl3) 5C ppm: 196.10, 160.34, 155.23, 151.76, 150.92, 135.47, 134.16, 134.07, 133.15, 132.86, 132.36, 131.67, 129.07, 128.94, 128.84, 128.81, 128.76, 128.52, 127.19, 125.43, 124.17, 114.23, 78.47, 71.97, 58.70, 55.37, 40.12, 31.58, 31.37, 26.64, 23.51, 10.96. IR (KBr) v cm-1: v=3260-3420,
5 5 5 v ' max NH 5
vOH=2940, vC=O=1655, 1595. Found: C 75.08, H 6.84, N 3.38 %. C52H56N2O8 requires C 74.62, H 6.74, N 3.35.
The X-ray diffraction study of 5-N-(2-methoxyethyl)-N'-urea-17-{(E)-[(3E)-3-(4-methoxybenzylidene)-2-oxocyclopentyli-dene]methyl}-25,27-dipropoxy-26,28-dihydroxycalix[4] arene, 5b (CCDC 1025174). The colourless crystals of 5b 4C1n4H.. .O.,N4-2CH3OH4H.O are orthorhombic. At 120 K:
104 112164 3 2
a=49.612(9), b=9.668(2), c=19.614(3) A, V=9408(3) A3, Mr=1715.98, Z=4, space group Pbcn, dcalc=1.212 g/cm3, ^ (MoKa)=0.083 mm-1, F(000)=3652. Intensities o f 78208 reflections (8294 independent, Rint=0.145) were measured (ro-scaning, 2©max=50°). The restrictions on the Csp3-O and Csp3-Csp3 bond lengths (1.43 A and 1.54 A, respectively) for the disordered propyl group were applied. The solvate methanol molecule and disordered over some positions water molecule are refined in isotropic approximation without hydrogen atoms. Full-matrix least-squares refinement of the structure against F2 in anisotropic approximation for non-hydrogen atoms using 8125 reflections converged to wR2=0.212 (R1=0.084 for 2717 reflections with F>4a(F), S=0.846).
Results and Discussion
To introduce the ketocyanine moiety to the macrocyclic backbone we employed the Knoevenagel reaction between readily available nitroformyl propoxycalix[4]arene 1[18] and a,p-unsaturated cyclopentanones 2a,b[19] in the presence of dimethylammonium dimethylcarbamate (DIMCARB)[17,20] as a co-solvent and catalyst (Scheme 1).
In the 1H NMR spectra of compounds 3a,b, the AB spin system of the axial and equatorial H-atoms of the ArCH2Ar methylene groups appeared as two doublets at 5 4.33 and 5 4.31 (Hax) and a multiplet at 5 3.41 (Heq) with 2JHH 12.813.4 Hz. The chemical shift difference between H and H
ax eq
of about 0.9 ppm reflects the flattened cone conformation of 3a,b in solution.[21] 13C NMR resonances for the carbons of the methylene bridges appeared at 5 31.31-31.48 ppm, which reflects the syn orientation of the adjacent phenolic rings in the cone conformation.[22]
Diffraction quality crystals of 3a,b were grown from chloroform-methanol mixtures. The X-ray diffraction study showed that the molecules existed in EE-form in the solid state. Macrocycles 3a and 3b adopt a cone conformation (Figure 1). The distance between centres of opposite benzene rings (6.65 A and 6.70 A for 3a and 6.89 A and 6.46 A for 3b) and angles between their planes (50.2° and 66.4° for 3a and 72.9° and 46.0° for 3b) are close enough. Conjugation of the aromatic n-system with the ketocyanine fragment is revealed in both compounds. The nitro-group is coplanar to the aromatic ring.
We have used calixarene ketocyanines 3a,b for the synthesis of corresponding urea derivatives. Calixarenes decorated with urea fragment are well known as anion receptors[23] and therefore are of particular interest in their binding and sensing. Also anion-receptor interactions underlie many catalytic processes in v/'vo.[24 25]
Reduction of nitrocalixarene ketocyanines 3a,b was performed with hydrazine hydrate in the presence of Raney nickel under reflux in methanol forming aminocalixarenes 4a,b. Amines 4a,b are unstable in the open air compounds and were treated with isocyanate without isolation.[26] Reaction of aminocalixarenes 4a,b with equimolar quantity of 2-methoxyethyl isocyanate proceeds at room temperature in chloroform giving the corresponding urea derivatives 5a,b with yields 68 % and 88 %, respectively (Scheme 1).
In the 'H NMR spectra of compounds 5a,b (Figure 2) recorded in CDCl3, the signals of equatorial ArCH2Ar protons are revealed as two multiplets in the field 3.32-
3.43 ppm which strongly overlapped with the signals of CH2CH2 residue of urea moiety. The axial ArCH2Ar protons appeared as two doublets at 4.29 and 4.32 ppm. The NH protons of urea fragment in 5a and 5b molecules were observed as triplets at 4.95 and 5.07 ppm with 3JHH 5.4 Hz and singlets at 6.14 and 6.36 ppm, respectively. The broad singlet at 3.10 ppm corresponds to cyclopentanone ring protons. The signals of hydroxyl protons are revealed as two singlets in the field 8.3-8.9 ppm. 13C NMR resonances for the carbons of the methylene bridges appeared at 5 30.9631.58 ppm, which reflects the syn orientation of the adjacent phenolic rings in the cone conformation. In IR spectra (KBr) of calixarenes 5a,b there are characteristic bands in regions 3260-3420 cm-1 (v ), 2940 cm-1 (v ), 1655, 1595 cm-1
V NH/? v OH7' >
(VC=O).
Unexpected results were obtained by X-ray study of single crystal 5b obtained from ethyl acetate solution. According to the spectral data the compound 5b exists as mono molecule in the solution. But in the crystal phase there was observed a centrosymmetrical molecule formed due to cyclization of carbon-carbon double bounds of ketocyanine moieties of two neighbouring 5b molecules (Figure 3). The presence of conjugated p-system of ketocyanine fragment and relative position of neighbouring molecules 5b create conditions for stacking interaction between them. Earlier[27] the possibility of the photo-dimerization of molecules in crystal phase under such conditions was shown. The dimer of 5b is located in special position on the 2-fold axis which passes through the centre of formed cyclobutane fragment. It can be assumed that the dimerization of 5b results in the deformation of its cone conformation (Figure 3). The distance between centres of opposite benzene rings (7.30 A and 5.93 A) and angles between their planes (87.1° and 28.1°) are rather different in contrast to 3a and 3b.
To estimate the influence of the calixarene framework on the absorption and fluorescence properties of 3a,b and 5a,b the model compound 6,[17] which can be considered as isolated ketocyanine fluorophore of 3b, was used for comparison (Scheme 2).
OMe
Scheme 2. The model compound 6.
Figure 1. X-ray crystal structures of the compounds 3a (above) and 3b (down); H-atoms are omitted for clarity. The EE-conformations are clearly shown. Thermal ellipsoids are shown at the 50 % probability level.
The UV-Vis and steady state fluorescence spectra of compounds 3a,b, 5a,b, and 6 were studied in toluene, chloroform, acetonitrile, DMSO, and methanol. Relative fluorescence quantum yields were measured using Coumarin 1 in ethanol (®f=73 %[28]) as a reference. Selected spectral data are given in Table 1.
All the products absorb on the border of the UV and visible regions, and demonstrate green or yellow fluorescence. At that, the compounds comprising dimethylamino-benzylidene terminal group (3a, 5a) possess a substantial positive solvatochromism. Solvatochromic shifts of dyes 3b and 5b are feeble and depend irregularly on solvent polarity, what can be rationalized taking into account polyenic (low
Figure 2. Representative section of 1H NMR spectrum of 5a in CDCl3.
Table 1. UV-Vis and fluorescent spectral characteristics of compounds 3a,b, 5a,b, and 6 measured in solvents of various polarity at 20 °C.
Figure 3. Centrosymmetrical dimer of 5b in crystal phase. H-atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level.
polar) character of the ground state of ketocyanines without strong electron-donating moieties in their chromophore. At the same time all the compounds possess strong positive solvatofluorochromism typical for ketocyanine dyes (Table 1 and Figure 4).
Equivalence of the fluorophore unit in compounds 3b, 5b, and 6 allowed us to study the differences in solvation of carbonyl oxygen of the ketocyanine unit in calixarene derivatives and model compound 6 (see Table 1, data in CHCl3 and MeOH and SI file). In all cases the presence of calixarene core gives a 10-20 nm red shift of the absorption and fluorescence maxima. The highest values of the shift are observed for the fluorescence of the calixarene based compounds in polar DMSO or MeOH. This effect displays a solvent-mediated influence of the remote polar group on the electronic state of ketocyanine fluorophore and demonstrate clearly the possibility of control of fluorescence colour by varying the nature of the analyte bound in the proximity to the fluorophore unit.
Comp. Solvent Xabs max (nm) max (nm) ®f (%) SS (cm-1)
3a PhCH3 442 492 0.8 2300
CHCl3 448 538 4.8 3730
MeCN 440 582 5.0 5550
DMSO 451 594 5.6 5340
MeOH 456 602 0.5 5320
3b PhCH3 398 448 <0.1 2800
CHCl3 401 476 0.5 3930
MeOH 402 521 0.3 5680
5a PhCH3 442 491 0.6 2260
CHCl3 450 537 5.0 3600
MeCN 441 582 5.6 5490
DMSO 453 593 6.7 5210
MeOH 459 604 1.5 5230
5b PhCH3 398 440 <0.1 2400
CHCl3 404 478 0.5 3830
MeOH 403 511 0.3 5240
6 CHCl3 384 462 0.03 4400
MeOH 393 497 0.8 5320
Aabs - absorption maximum; - fluorescence maximum;
max r 7 max
®f - fluorescence quantum yield; SS - Stokes' shift.
The polarization of chromophore unit provide a regular increase of Stokes' shifts with increasing solvent polarity. The fluorescence quantum yields, while relatively small, are several times higher for the calixarene ketocyanines than for the model compound 6, showing the spatial influence of the rigid calixarene skeleton on the fluorescence properties.
X (nm)
Figure 4. Normalized UV-Vis and fluorescent spectra of compound 5a in toluene, CHCl3, and MeOH.
To evaluate photochemical stability of calixarene ketocyanines, the 1.2-10-5 M solution of compound 5a in DMSO was subjected to UV irradiation (250 W laboratory UV lamp, 1 cm quartz cuvette, sample-to-lamp distance circa 40 cm). Absorption spectra of the tested solution of 5a after 3 hr of irradiation proved its relatively low photochemical stability - the solution retained only 60 % of its initial optical density at the absorption maximum.
Conclusions
In summary, the synthetic approaches to calix[4]arene ketocyanines functionalized with nitro-, amino- or urea moieties at the wide macrocycle rim were elaborated. The UV-Vis and fluorescence studies have been carried out for the compounds synthesized. The estimated solvatofluoro-chromism levels and quantum yield values demonstrate clearly a possibility of control of fluorescence colour and intensity by varying the nature of the analyte bound in the proximity of the fluorophore unit.
Acknowledgements. This work was supported by the NAS of Ukraine through the grant "Chemosensor system such as "electronic nose" for biomedical and of environmental application". The authors thank Mr. O. Dukhno for experimental assistance.
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Received 13.05.2016 Accepted 22.06.2016
