Cyanine dyes of zero/bis-zero methine incorporating imid-azo(1,2-a)Pyridine (quinoline) or pyrazino(1,2-a)pyridine (quinoline) with stable C-N bond were synthesized using keto-oxime methylene C-link heterocyclic quaternary salts [1-phenyl-3-methyl-pyrazolino-4-keto-oxime- α-methylene-bis-pyridin-(quinoin)-1(4)-di-ium-iodide(ethiodide) salts and 1-phenyl-3-methyl-pyrazolino- 4-ketooxime- α-methylene-N-2-methyl-bis pyridin (quinoin)-1(4)-di-ium-iodide(ethiodide) salts]. Such heterocyclic precursors and related dyes were identified by elemental and spectral analyses. The absorption spectra properties of such dyes were investigated in 95% Ethanol to attempt and throw some light on the influence of such new heterocyclic nuclei and to compare or evaluate spectral behaviors. The absorption spectra of dyes in different pure solvents were examined in the visible region showing solvatochromism and the colour changes of dyes with solvents having different polarities. This permits a selection of the optimal solvent (fractional solvent) when such dyes are applied as photosensitizers. The spectral behavior of some selected newly synthesized cyanine dyes is observed in mixed solvents of different polarities and progressively increasing quantities of one solvent over the other were studied and showed an increase in the absorbance of CT band with increasing proportion of that solvent. Evidence for hydrogen bond formation between the solute molecules and solvent molecules allows measurement of certain energies such as hydrogen bonding, orientation, and free energies.
Special attention is given to the implementation, preparations, and applications of heterocyclic cyanine dyes to show the various aspects in order to satisfy the great demand in industrial, physiology, biochemistry and various biological fields. Cyanine dyes are colorant compounds used in staining of internal limiting membrane (ILM) [
N-Bridgehead heterocyclic cyanine dyes are an important class of dyes which are characterized by the presence of nitrogen atom inside the ring. N-bridge head heterocyclic compounds used as precursors possess high site reactivity susceptible to be attacked by either Electrophile/Nucleophile in the substitution/addition reactions which give high stability nature for the dyes [
In this paper, we designed and synthesized novel highly stable cyanine dyes. Keto-oxime methylene C-link heterocyclic quaternary salts were used in the synthesis of N-bridge head heterocyclic incorporating imidazolo(1,2-a)pyri- dine(quinoline) or pyrazino(1,2-a)pyridine(quinoline) as main entities for zero and bis-zero methine cyanine dyes synthesis. The spectral, solvatochromic behavior and mixed solvent effect are described.
All melting points are uncorrected Elemental and spectral analysis was carried out at the microanalytical center (Cairo University). The IR (νKBr) spectra were determined with Perkin Elmer Infrared 127ß spectrophotometer (Cairo-University). 1H-NMR spectra were recorded with a Bruker AMX-250 spectrometer (Cairo-University). Mass spectra were recorded on an HpMs 6988 spectrometer (Cairo University). The absorption spectra were recorded immediately after preparation of the solutions within the wavelength range (350 - 700) on 6405 UV/Visible recording spectrophotometers, Faculty of Science, Aswan University.
Analytical data and molecular Properties for all the starting N-bridge head heterocycles and the target dyes involved in this study was obtained and summarized in (
Comp. No. | M.P ˚C | Yield % | Color | Mol. Formula (Mol. Wt.) | Calcd. (Found)% | Absorption spectra in EtOH | |||
---|---|---|---|---|---|---|---|---|---|
C | H | N | λmax (nm) | εmax (M−1 cm−1) | |||||
1 | 125 | 78 | Pale brown | C23H24IN5O (513) | 53.81 53.82 | 4.71 4.70 | 13.64 13.66 | 350 | 1778 |
2a | 129 | 60 | Brown | C28H28I2N6O (718) | 46.81 46.80 | 3.93 3.95 | 11.70 11.71 | 365 | 1785 |
2b | 135 | 58 | Red | C32H30I2N6O (768) | 50.02 50.09 | 3.94 3.94 | 10.94 10.95 | 365 440 | 1795, 797 |
3a | 140 | 75 | Dark red | C29H30I2N6O (732) | 47.56 47.54 | 4.13 4.14 | 11.47 11.48 | 365 490 | 1667, 923 |
3b | 145 | 82 | Brown | C19H16N6O2 (360) | 63.26 63.29 | 4.43 4.47 | 23.30 23.32 | 365 495 | 1789, 1100 |
4a | 165 | 71 | Brown | C28H25IN6 (572) | 58.75 58.73 | 4.40 4.41 | 14.68 14.69 | 470 | 1092 |
4b | 190 | 66 | Brown | C32H27IN6 (622) | 61.74 61.76 | 4.37 4.35 | 13.50 13.52 | 485 | 1397 |
5a | 127 | 61 | Red | C21H18N6O3S (434) | 58.00 58.09 | 4.14 4.15 | 19.33 19.30 | 460 | 698 |
5b | 170 | 65 | Reddish | C21H18ClN5OS (423) | 59.446 59.445 | 4.24 4.27 | 16.51 16.55 | 498 | 1010 |
6a | 155 | 74 | Red | C21H18N6O3S (434) | 58.001 58.000 | 4.14 4.13 | 19.33 19.36 | 390, 520 | 2700, 2443 |
6b | 150 | 59 | Red | C40H37I2N7 (869) | 55.25 55.25 | 4.29 4.30 | 11.28 11.30 | 480 | 670 |
6c | 130 | 59 | Pale brown | C21H17Cl2N5O (426) | 59.11 59.10 | 3.987 3.89 | 16.420 16.41 | 500 | 1780 |
6d | 185 | 68 | Brown | C40H39I2N7 (871) | 55.12 55.14 | 4.51 4.5 | 11.25 11.23 | 475 | 612 |
6e | 185 | 75 | Red | C44H39I2N7 (919) | 57.47 57.45 | 4.27 4.28 | 10.66 10.69 | 478 | 1593 |
6f | 160 | 61 | Red | C44H39I2N7 (919) | 57.47 57.48 | 4.27 4.28 | 10.66 10.65 | 474 | 1012 |
A mixture of 3-methyl-1-phenyl-pyrazolino-5-imino-4-(N-acetyl-quinolin-1-ium iodide, 1 mole), hydroxylamine hydrochloride (2 moles) and sodium acetate (3 moles) was dissolved in ethanol (30 ml) and heated in a water bath for an hour. The reaction mixtures were filtrated from unreacted materials. The reaction mixture quenched by water and extracted by chloroform (3 × 50 ml). The combined organic layers were washed with water, dried over MgSO4 and evaporated under reduced pressure. The product was purified via recrystallization from ethanol.
Ethanolic solution of compound 1 (1 mol) with pyridine (quinoline) or 2methyl pyridine (2-methyl quinoline) (1 mol) and iodine (1mol). The mixture was stirred and refluxed for 3 - 5 hrs. The reaction mixtures were filtrated from unreacted materials. The filtrate was concentrated to one third of its volume, cooled. The precipitated products after dilution with water were separated, filtrated, recrystallized from diethyl ether.
Fusion of 2a, b with piperidine for about an hour then dissolved the reaction mixture in anhydrous ethanol and reflux for 3 hours. The reaction mixture quenched by water and extracted by methylene chloride (50 ml). The combined organic layers were washed with water, dried over MgSO4 and evaporated. The product was purified via recrystallization from petroleum ether.
Fusion of 3a, b with piperidine for about an hour then dissolved the reaction mixture in ethanol and reflux for 3 hours. The reaction mixture concentrated to half of its volume, cooled and precipitated with ice water then recrystallized from petroleum ether.
Ethanolic solution of dye 5a, b (1 mol) and pyridin [quinolin]-2(4)-ium-1-ethiodide salts (1 mol) in the presence of few drops of piperidine were stirred and refluxed for 5 - 7 hrs. The reaction mixtures were filtrated from unreacted materials. The filtrate concentrated to one third of its volume, cooled and acidified with acetic acid. The precipitated products after dilution with water were separated, filtrated, recrystallized from petroleum ether.
UV-Vis spectra for all dyes in pure and mixed solvents were recorded at 25˚C in a 1 cm path length quartz cell on a Cary 3 Spectrophotometer. Ethanolic solution of 1 × 10−5 M was prepared, and the absorbance was measured and the extinction coefficient was calculated in each case.
The organic solvents were used of spectroscopic grade which purified according to the recommended methods [
For studying the effect of pure solvents in the UV and visible range: An accurate volume of the stock solution (10-3 M in ethanol) of the dyes were diluted to appropriate volume in order to obtain the required concentration. The spectra were recorded immediately after mixing in order to eliminate as much as possible the effect of time. A range of organic solvents was investigated, including water, dimethylformamide (DMF), ethanol, acetone, carbon tetrachloride, chloroform and benzene. Moreover, to study the spectral behavior in mixed solvents in the visible region: An accurate volume of stock solution (10-3 M in ethanol) of the dyes were placed in 10 ml measuring flask containing the required volume of ethanol, then completed to the mark with the other solvent.
The synthesis of zero methine (4a, b & 5a, b) and bis-zero methine (6a-f) cyanine dyes was started by preparation of 3-methyl-1-phenyl-pyrazolin-4,4-keto- methylene-quinolin-1-ium ethiodide salts (1) according to reference [
Scheme 1. Synthetic routes of dyes (4a, b), (5a, b) and (6a-f). Where, (2, 3, 4, 5a, b): Ar = 2, 3 di[H] (a); A = 2, 3-C4H4 (b); (6a-f): Ar = 2, 3 di[H], B = 1-ethyl pyridin-4-ium salt (a); A = 2, 3 di[H], B = 1-ethyl-quinolin-4-ium salt (b); A = 2, 3 di[H], B = 2-ethyl-quinolin-1-ium salt (c); A = 2, 3-C4H4, B = 1-ethyl pyridin-4-ium salt (d); A = 2, 3-C4H4, B = 1-ethyl-quinolin-4-ium salt (e); A = 2, 3-C4H4, B = 1-ethyl-quinolin-1-ium salt (f).
The structures of 1, 2b, 3b, 4b, 5b & 6e was characterized & identified by elemental analysis (
2-[3-Methyl-1-phenyl-pyrazolin-5-imine] imidazo(1, 2-a)Pyridin (quinolin)- zero-3[4(1)] methine cyanine dyes (4a, b) & 3-[3-Methyl-1-phenyl-pyrazolin-5- imine] pyrazino(1,2-a)Pyridin (quinolin)-zero-4-[4(1)] methine (5a, b) and 2-[H]-3-[3-methyl-1-phenyl-pyrazolin-5-imine] pyrazino (1, 2-a)Pyridine (quinoline)-bis-zero-1,4[4(1)] methine cyanine dyes (6a-f) are highly colored compounds. Their color ranging from (reddish-red), easily (partially) soluble in polar (non) organic solvents exhibiting colored solutions concomitant with slight or intense greenish-red fluorescence depending upon the solvent used. They are soluble in concentrated H2SO4 acid liberating iodine vapour on warming. Their ethanolic solutions gave permanent colours in basic media which reversibly discharged on acidification. Thus, the visible absorb-maximum of dye 4a [A = pyridin-4-ium salt] showed (λmax= 470 nm; εmax = 1092 M−1 cm−1). Substitution of [A = pyridin-4-ium salt] in dye 4a by [A = quinolin-4-ium salt] in 4b exhibit (λmax = 492 nm; εmax= 1397 M−1 cm−1) resulted in bathochromic shift of Δλmax =22 nm. This is due to the more extensive π-delocalization and extra conjugation in the quinoline ring. Moreover, the visible absorb-maximum of 5a [A = pyridin-4-ium salt] showed (λmax= 460 nm; εmax = 698 M−1 cm−1). Substitution of [A = pyridin-4-ium salt] in dye 5a by [A = quinolin-4-ium salt] in dye 5b exhibit (λmax = 498 nm; εmax= 1010 M−1 cm−1) resulted in bathochromic shift of Δλmax =38 nm. This is due to the more extensive π-delocalization and extra conjugation in the quinoline ring. Finally, dye 6a [A = 2, 3 di[H], B = 1-ethyl pyridin-4-ium salt] showed (λmax = 390 & 520 nm; εmax = 2700 & 2443 M−1 cm−1). Substitution of [A = A = 2, 3 di[H], B = 1-ethyl pyridin-4-ium salt] in dye 6a by [A = 2, 3 di[H], B = 1-ethyl-quinolin-4-ium salt] in dye 6b exhibit (λmax = 480 nm; εmax = 670 M−1 cm−1) resulted in bathochromic shift of Δλmax = 40 nm. This is due to the more extensive π-delocalization and extra conjugation in the quinoline ring. Substitution of [A = 2, 3 di[H], B = 1-ethyl pyridin-4-ium salt] in dye 6a by [A = 2, 3 di[H], B = 1-ethyl-quinolin-4-ium salt] in dye 6c exhibit (λmax = 500 nm; εmax = 1780 M−1 cm−1). Substitution of [A = 2, 3 di[H], B = 1-ethyl-quinolin-4-ium salt] in dye 6c by [A = 2, 3-C4H4, B = 1-ethyl pyridin-4-ium salt] in dye 6d exhibit (λmax = 475 nm; εmax = 612 M−1 cm−1) resulted in hypsochromic shift of Δλmax = 25 nm. This is due to the less extensive π-delocalization and less conjugation in the quinoline ring. Substitution of [A = 2, 3-C4H4, B = 1-ethyl pyridin-4-ium salt] in dye 6d by [A = 2, 3-C4H4, B = 1-ethyl-quinolin-4-ium salt] in dye 6e exhibit (λmax = 478 nm; εmax = 1593 M−1 cm−1) resulted in hypsochromic shift of Δλmax = 3 nm. This is due to the more extensive π-delocalization and extensive conjugation in the quinoline ring. Substitution of [A = 2, 3-C4H4, B = 1-ethyl-quinolin-4-ium salt] in dye 6e by [A = 2, 3-C4H4, B = -ethyl-quinolin-1-ium salt] in dye 6f exhibit (λmax = 474 nm; εmax = 1012 M−1 cm−1) resulted in hypsochromic shift of Δλmax = 4 nm. This is due to the less extensive π-delocalization and less conjugation in the isoquinoline ring. Comparison of dyes (4a, b) and (5a, b), Observed that dyes (4a, b) giving higher values of λmax than dyes (5a, b) this can be explained from the extending of π-delocalization through three rings in case of dyes (4a, b). Moreover 3-Methyl-1-phenyl-pyrazolin-5-imine-4-pyrazino(1,2-a) Pyridine (quinoline)- bis-zero-2,5[4(1)]methine cyanine dyes (6a-f) are bathochromic shift to 3-Methyl-1-phenyl-pyrazolin-5-imine-4-pyrazino(1,2-a) Pyridine (quinoline)- zero-2[4(1)] methine cyanine dyes (5a, b) this back to extend of π-delocalization in case of bis zero methine cyanine dyes (6a-f).
The color changes of cyanine dyes with solvents (solvatochromism) was previously discussed by [
Solvent | 5b | 6e | ||
---|---|---|---|---|
λmax | εmax | λmax | εmax | |
C6H6 | 470 | 984.7 | 462 | 642.03 |
Water | 474 | 669.9 | 469 | 534.2 |
CCl4 | 449 | 647.9 | 465 | 220 |
DMF | 501 | 869.49 | 500 | 568 |
EtOH | 498 | 918.86 | 478 | 925.5 |
CHCl3 | 470 | 977.42 | 472 | 947 |
Acetone | 492 | 771.46 | 478 | 802 |
dyes are showed positive solvatochromism with increased solvent polarity, which depend on the structure and the type of dye. This indicates that the polar excited states of these cyanine dyes are stabilized by polarization interaction forces as the polarizability of the solvent is increased. This behaviour occurs as a result of electrostatic interactions of the distributed cationic charges with the dipoles of the solvated molecules which lead to formation of specific solvated forms of dyes. The absorption spectra of the dyes in ethanol are characterized by the presence of one or two essential bands which reflects the presence of intermolecular charge transfer. This intermolecular charge transfer had arisen from transferring the electron lone pair of the nitrogen atoms of the heterocyclic ring system towards the positively charged residue along the conjugated chain between both. The representing graphs disclosed that these electronic charge transfer bands exhibit a hypsochromic shifts in ethanol relative to DMF, CHCl3, and CCl4. This shift can be attributed to the following factors: The bathochromic shift occurred in DMF relative to ethanol is mainly a result of the increase in solvent polarity due to increasing the dielectric constant of the former. The hypsochromic shifts appeared in ethanol relative to CHCl3 & CCl4 is generated from the solute-solvent interaction through intermolecular hydrogen bonding between ethanol and the lone pair of electrons within the heterocyclic ring system. Otherwise, this decreases the mobility of the electron cloud over the conjugated pathway towards the positively charged center. It was worth mentioning that the intermolecular hydrogen bonding between CHCl3 molecules and the lone pair of electrons of nitrogen atoms of the heterocyclic ring system is difficult due to the steric hindrance of the three bulk chlorines. Moreover, the solute solvent interactions in cases of CHCl3 & CCl4 generated a residual negative charge on the nitrogen atoms of the heterocyclic ring system which intern facilitated the electronic charge transfer to the positively charged center and this explain the bathochromic shifts in these solvents relative to ethanol. The unexpected hypsochromic shifts in the absorption spectral maxima in water relative to ethanol and its lower extinction coefficients were mainly ascribed to the ease of interactions of water molecules, through intermolecular hydrogen bonding, with the lone pair of electrons of the nitrogen atoms of the heterocyclic ring system, through intermolecular hydrogen bonding, which intern preclude the charge transfer from the heterocyclic ring system to the positively charged residue along the conjugated bridge.
The absorption spectra of dye (6e) in 1 × 10−4 M DMF in the presence of different concentrations of benzene are shown in (
It was obvious that in presence of 12.97 M of DMF, the spectrum exhibits a band located at 500 nm. In the presence of 1.16 M of DMF, the band is shifted to 463 nm concomitant with a gradual blue shift. Also, an increase in band intensity at fixed wavelength (500 nm) is observed on increasing of C6H6 concentration as depicted in (
blue shift in the maximum absorption wavelength on increasing the C6H6, content can be described to the gradual formation of the complex species through intermolecular hydrogen-bond. The graphical representation of absorbance at 500 nm against the mole fraction of DMF (
the solvation sheaths around the molecules. The added molecules may first enter the outer solvation sheaths and then will introduce themselves in the first sheaths as their proportions are increased. This is probably due to the fact that addition of DMF permits the formation of a solvent cage around the solute molecules, through intermolecular hydrogen-bonding as shown in (
− Δ G = R T ln K f (1)
where R is the constant of ideal gas, T is the absolute temperature and lnKf calculated from log Kf (log Kf = 1.464; Kf = 29.1), and the calculation gives −∆G = 0.345 K cal mol-1. The number of C6H6 molecules (n) complexed with the solute is computed from (
Highly stable series of novel zero/Bis zero methine cyanine dyes stabilized by C-N bond were synthesized based on N-Bridge head heterocyclic compounds. The stability of dye formation is due to that N-bridge head heterocyclic compounds used as precursors possess high site reactivity susceptible to be attacked by either Electrophile/Nucleophile in the substitution/addition reactions. The absorption spectra of the synthesized dyes were investigated in different organic solvents and a mixed solvent system. The results indicated that the colour of these dyes depends on the length of conjugation within the structure. Dyes having unsaturated terminal groups are more bathochromic than those with saturated terminal groups. The absorption spectra of these dyes in different organic
Dye | Solvent System | Excitation energy K Cal mol−1 Pure Solvents | Orient energy K Cal mol−1 | H-bond energy K Cal mol−1 | Total energy K Cal mol-1 | N | Log Kf (−) | Kf (−) | ΔG K Cal mol−1 (±) | |
---|---|---|---|---|---|---|---|---|---|---|
6e | (DMF-Benzene) | 57.2 (DMF) | 61.9 (Benzene) | 3 | 2.3 | 5.2 | 2 | 1.464 | 29.1 | 0.3454 |
solvents undergo bathochromic or hypsochromic shift depending on the structure of dye and the type of solvent. The results of spectral behaviour in a mixed solvent system indicate the formation of a hydrogen bonding between the solute and solvent molecules and allow the measurement of certain energies, such as hydrogen-bonding, orientation and free energy.
The authors declare no conflicts of interest regarding the publication of this paper.
Koraiem, A.I., Abdellah, I.M. and El-Shafei, A.M. (2018) Synthesis and Photophysical Properties of Novel Highly Stable Zero/Bis-Zero Methine Cyanine Dyes Based on N-Bridgehead Heterocycles. International Journal of Organic Chemistry, 8, 282-297. https://doi.org/10.4236/ijoc.2018.83021