INTRODUCTION:

Quinolines and benzo/hetero fused analogues have attracted great attention of medicinal and synthetic chemist because of their presence in natural products and have good physiological activities. The Vilsmeier Haack reagent has been proved to be versatile synthetic reagent and used for the various synthetic transformations¹. It has variety of synthetic applications such as used for formylation², cyclohaloaddition³, cyclisation⁴, condensation, ring annulations⁵, etc. There are many routes has been developed for the fictionalization of quinolines, the Vilsmeier approach is found to be most efficient for achieving useful transformation and heteroannulations.

The versatile application in the synthesis has been proved by the synthesis of 4-(N,N-dimethylaminomethylene)-2-alkyl/aryl-2-oxazolin-5-one⁶from the N-acyl derivatives of α-amino acid esters and α-aminoacetanilides. Wall J et al has been developed novel quinoline based fused heterocyclic system as potential anticancer agents⁷. Harrowven D C et al suggested that quinoline nucleus with different substituents at 2- and 3- positions was versatile synthon for the heteroannulation⁸. Ambika Srivastava et al has been carried out the transformation of the 2-chloro and 3-formyl groups into different functionalities⁹. T Suresh et. al has been carried out the annulations of 3-formyl-2-hydroxycoumarin and its derivatives.

The word phosphor was invented in the early 17^th century. There are some characteristics of typical phosphor as- must survive hazardous chemical environment, cannot be water soluble, durable, easy to apply, not easily detected or noticed without specialized equipment, etc. Phosphors become technologically and industrially important with the introduction of fluorescent lamps in 1938. Thermometry was suggested in the German patent in 1938. First peer-reviewed article, to our knowledge appeared in 1949. Between 1950 to 1980, it was not widely used. Its most common use was aerodynamic applications. Advances in lasers, microelectronics, and other supporting technologies enable additional commercial as well as scientific use. The physics and chemistry of luminescence materials and their applications become and still is the core area covered by Luminescence symposia.

In the small molecules organic light emitting diodes, the family of carbazoles¹⁰ could be extended to be suitably fit for red^11-13, green^14-16, and blue light^17-19 triplet emitters and therefore, they can be used in full color displays^{20-23, 25-28}. More recently studies of Thompson, Forrest and co-workers shows that the use of electron blocking layers (EBLs) consisting of Ir^III complexes with picolinate ligands produced improved color purities in the case of blue light emitting device²⁹. Some of the organic molecules are used as EBLs as- fluorinated phenylenes²⁴, and oxadiazole as well as triazole containing molecules such as trimer of N-arylbenzimidazoles (TPBi)^30,31, 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD)³², 3-phenyl-4-(1’-naphthyl)-5-phenyl-1,2,4-triazole (TAZ)^33,34, 1,8-Naphthalimides³⁵, polyquinolines³⁶, or carbon nanotubes doped in PPV³⁷ were also found to be useful as hole blocking layers (HBLs).

Searching for highly efficient fluorescence organic compounds (Schiff bases) is a topic of current interest. The aromatic based ligand having electron donating or withdrawing groups has been increased or decreased the intensity of absorption or shifted absorption wavelength on either side. Luminescence properties of the various Schiff bases of 2-chloro-3-formylquinoline have been checked by using Spectrofluorometer model number RF5301. A Xe laser lamp was used for excitation and emission spectra were scanned from the range 220nm to 750 nm. The emission of Schiff bases at each excitation wavelength has been checked.

In this paper we tried to synthesis of various Schiff bases of 2-chloro-3-formylquinoline of amines and hydrazones which has general name as N-[(E)-(2-chloroquinolin-3-yl)methylidene]anilides (2a-e) and study their fluorescence properties.

The required acetanilide (pure state) was synthesized from the reaction of aniline and acetic anhydride in aqueous medium. The Vilsmeier cyclisation of acetanilide was carried out by slowly adding POCl₃ (with constant stirring) to a substance in DMF at 0-5⁰C followed by heating to 90⁰C to obtain 2-chloro-3-formylquinoline (1) in good yield. The structure of the compound can be confirmed by spectral data and chromatographic technique. The haloanilines and hydrazones are synthesized by following known methods (referring Vogel’s Organic Chemistry practical book, 5^th edition). The formation of Schiff bases (2a-e) can be confirmed by monitoring TLC during the reaction and at the end of reaction. The structures of Schiff bases (2a-e) can be confirmed by using NMR data.

1. Synthesis of 2-chloro-3-formylquinoline (1)

To a solution of acetanilide (5 mmol) in dry DMF (15 mmol) at 0 – 5 ⁰C, POCl₃ (60 mmol) was added dropwise with stirring and mixture was then stirred at 80 – 90 ⁰C for 9 hrs. The resulting mixture was poured in crushed ice, stir for 5 min and resulting solid was filtered, washed well with water and dried. The compound was recrystalized from ethyl acetate. The m.p. and yield of the compound is 148 ⁰C and 78% respectively.

PMR (DMSO-D6): 10.4 (s, 1H), 8.75 (s, 1H), 8.15 (m, 1H), 7.97 (m, 1H), 7.92 (m, 1H), 7.78 (m, 1H).

2. Synthesis of Schiff bases N-[(E)-(2-chloroquinolin-3-yl)methylidene]anilides of 2-chloro-3-formylquinoline and haloaniline (2a-e).

Dissolve 0.01 mol of 2-chloro-3-formylquinoline derivative in 30 ml of absolute alcohol in 50 ml round bottom flask fitted with spiral reflux condenser and calcium chloride guard tube. Add 0.011 mol haloaniline or hydrazones and catalytic amount of acetic acid. Reflux the reaction mixture in water bath for about 30 minutes. Cool the reaction mixture and filter the resulting solid by using Whatmann filter paper number 41 on suction pump and recrystalized by using methanol. Dry it in hot air oven and record yield and m.p.

Result Table 01: Yield, m.p. and spectral analysis.

Starting Amine	Product	Yield	M.P. ⁰C	NMR data(δ in ppm)
Isoniazide		65% (2a)	162	10.3 (s, 1H); 8.9 (s, 1H); 8.2 (t, 2H); 7.7-7.9 (m, 4H); 7.69 (t, 2H).
4-iodoaniline		79% (2b)	136	9.1 (s, 1H); 8.9 (s, 1H); 8.1 (t, 2H), 7.9 (t, 2H); 7.2-7.8 (m, 4H).
4-chloroaniline		81% (2c)	146	9.1 (s, 1H); 8.9 (s, 1H); 8.2 (t, 2H), 7.9 (t, 2H); 7.3-7.8 (m, 4H).
4-bromoaniline		78% (2d)	142	9.1 (s, 1H); 8.9 (s, 1H); 8.1 (t, 2H), 7.9 (t, 2H); 7.3-7.8 (m, 4H).
3-chloroaniline		65% (2e)	117	9.1 (s, 1H); 8.9 (s, 1H); 7.4-7.8 (m, 4H); 7.2-7.36 (m, 4H).

Fig: 2. Emission spectra of N-[(E)-(2-chloroquinolin-3-yl)methylidene]pyridine-4-carbohydrazide at (a) 399 nm. (b) 764 nm. (c) 382 nm. (d) 800 nm.

Fig: 3. Excitation of 4-iodo-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline.

(a) (b)

Fig: 4. Emission spectra of 4-iodo-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline at- (a) 405 nm and (b) 442 nm.

Fig: 5. Excitation of 4-chloro-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline.

Fig: 6. Emission at 401 nm of 4-chloro-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline.

Fig: 7. Excitation of 4-bromo-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline.

Fig: 8. Emission at 401 nm of 4-bromo-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline

Fig: 9. Excitation of 3-chloro-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline

(a) (b)

Fig:10. Emission spectra of 3-chloro-N-[(E)-(2-chloroquinolin-3-yl)methylidene]aniline at- 400 nm and (b) 476 nm.

The fluorescence data can be shown in following table:

Slit width: Excitation and emission is 5 mm; Concentration of solution is 500 ppm; Solvent used is DMF.

Sample Name	Excitation wavelength (nm)	Emission wavelength (nm)
N-[(E)-(2-chloroquinolin-3-yl)methylidene]pyridine-4-carbohydrazide (2a)	382 (ε 128.94) 399 (ε 462.85) 764 (ε 82.34) 800 (ε 279.038)	386 (ε 164), 444 (ε 280), 731 (ε 5.93), 772 (ε 11.5) 401 (ε 507.8), 456 (ε 218.5), 803 (ε 12.6) 385 (ε 68.0), 432 (ε 138), 767 (ε 4.095) 401 (ε 240), 455 (ε 233), 804 (ε 8.01)
N-[(E)-(2-chloroquinolin-3-yl)methylidene]4-iodoaniline (2b)	405 (ε 18.3) 442 (ε 1.7)	411 (ε 77.0), 464 (ε 70.0) 452 (ε > 1015), 506 (ε 295)
N-[(E)-(2-chloroquinolin-3-yl)methylidene]4-chloroaniline (2c)	401 (ε 13.65)	404 (ε 28.73), 484 (ε 81.75)
N-[(E)-(2-chloroquinolin-3-yl)methylidene]4-bromoaniline (2d)	401 (ε 10.21)	407 (ε 154.5), 461 (ε 156), 488 (ε 153.32)
N-[(E)-(2-chloroquinolin-3-yl)methylidene]3-chloroaniline (2e)	400 (ε 139.97) 476 (ε 1.360)	404 (ε 999.34), 458 (ε 803. 048) 491 (ε > 1015.87), 503 (ε 638.70)

RESULT AND DISCUSSION:

All the synthesized compounds (2a-f) were purified by successive recrystallization using ethanol. The purity of the synthesized compounds was checked by performing TLC. The structures of the synthesized compounds were determined on the basis of their ¹HNMR data. The yield of the product depending on the nature of amine. The p-halo anilines (active anilines) are more reactive and gives good yield of product while for m-halo anilines (comparative deactivated anilines) gives moderate yield.

The excitation at ~ 400 nm showing by all Schiff bases with different intensities is due to basic skeleton of 2-hydroxyquinoline skeleton and is λ_max for them. The other excitations are due to in conjugate aryl rings of substituted anilines. The intense emissions by the Schiff bases are showing in the region 400-490 nm (maximum in violet region 380-450 nm & blue region 450-495 nm). The Schiff bases of 2-chloro-3-formylquinoline with various haloanilines (including chloro, bromo and iodohaloanilines) shows shifting of some absorption bands (wavelengths) towards lower (in case of chloro and bromo) and in some cases towards higher wavelengths. The effect of shifting is considerable in case of para-substitution rather than meta-substitution. N-[(E)-(2-chloroquinolin-3-yl)methylidene]4-chloroaniline (2c) shows absorption and emission at higher wavelength as compared to N-[(E)-(2-chloroquinolin-3-yl)methylidene]3-chloroaniline (2e) but intensity of meta-substituted Schiff base is higher than para-substituted Schiff base.

ACKNOWLEDGMENT:

The authors are thankful to the Principal, Govt of Mahrashtra, Ismail Yusuf Arts, Science and Commerce College, Mumbai 60, India, for his constant encouragement and inspiration. The authors are also thankful to the Head, Department of Chemistry, Institute of Science, Fort, Mumbai 32, India for providing facilities and helpful discussions during the synthesis. We also thanks our research group, Arti Nagarsekar, Sharada Shelke and Dipak Arakh.

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Received on15.11.2011 Modified on 20.01.2012

Research J. Pharm. and Tech. 5(3): March 2012; Page 369-375