Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 78–84

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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

journal homepage: www.elsevier .com/locate /saa

Growth, optical, luminescence, thermal and mechanical behaviorof an organic single crystal: 3-Acetyl-2-methyl-4-phenylquinolin-1-iumchloride

1386-1425/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.saa.2013.12.041

⇑ Corresponding author. Tel.: +91 416 2202350; fax: +91 416 2243092.E-mail address: kalainathan@yahoo.com (S. Kalainathan).

M. Nirosha a, S. Kalainathan a,⇑, S. Sarveswari b, V. Vijayakumar b

a Center for Crystal Growth, VIT University, Vellore 632 014, Indiab Centre for Organic and Medicinal Chemistry, VIT University, Vellore 632 014, India

h i g h l i g h t s

� 3A4MPQ have grown by slowevaporation solution growthtechnique.� The lattice parameters and

morphology have identified by singlecrystal X-ray diffraction.� The cut-off wavelength has found to

be 371 nm.� The melting point of the material is

156�C, and it is stable up to 228�C.� Micro hardness and etching studies

have performed for the grown crystal.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 12 September 2013Received in revised form 18 November 2013Accepted 5 December 2013Available online 17 December 2013

Keywords:Crystal growthOptical propertiesThermo gravimetric analysisLuminescenceMechanical studiesEtching studies

a b s t r a c t

A single crystal of 3-acetyl-2-methyl-4-phenylquinolin-1-ium chloride has grown by slow evaporationsolution growth technique using ethanol as solvent. The structural, thermal, optical and mechanicalproperty has studied for the grown crystal. Single crystal XRD revealed that the crystal belongs to mono-clinic system with space group P21/c. The presences of Functional groups in the crystallized material haveconfirmed using the FTIR vibrational spectrum. The optical absorbance spectrum recorded from 190 to1100 nm shows the cut-off wavelength occurs at 371 nm. The material shows its transparency in theentire region of the visible spectrum. The photoluminescence spectrum shows the ultraviolet and blueemission in the crystal. Thermogravimetric and differential thermal analysis reveal the thermal stabilityof the grown crystal. Etching study shows the grown mechanism and surface features of the crystal. Vick-ers microhardness studies have carried out on the (01-1) plane to understand the mechanical propertiesof the grown crystal. The hardness of the title compound increases on increasing the load. The Meyer’sindex number (n), and the stiffness constants for different loads has calculated and reported.

� 2013 Elsevier B.V. All rights reserved.

Introduction

Quinolines constitute an important class of nitrogen containingheterocyclic compounds due to their different application invarious areas. They find applications as pharmacological

activities, biological activities, polymer chemistry, electronics andoptoelectronics etc. [1–3]. Quinoline derivatives have found to pos-sess significant activities in antimicrobial, antimalarial, anti HIVand anticancer activities [4–7]. These kinds of nitrogen containingheterocyclic compounds exhibit extraordinary optical-electricproperties in nonlinear optical fields and attract interest to theirelectron-deficient nature which may be developed in organiclight-emitting diodes (OLEDs) and display technologies [8,9]. The

Fig. 1. Solubility curve of 3A4MPQ.

M. Nirosha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 78–84 79

challenging goal of OLED has clearly connected to the commercial-ization of full-color flat-panel displays. The OLEDs technology has alarge area of applications from small mobile phone displays to TVand monitors. The research in OLEDs has become one of the mostexciting topics in the field of chemistry, physics and materialsscience. Quinoline based molecules have suggested as electrontransport and hole blocking materials for electroluminescentdevices [10]. Recently Quinolines conjugated derivatives have gen-erated considerable interest as blue emitting material [11,12]. Inthis rapid growing field, some researchers focused on the syntheticmanipulation of quinoline derivatives with the aim of achievingstable OLEDs with high brightness and external quantumefficiency. Further improvement on the essential characteristicsneeds a detailed knowledge concerning the fundamental electronicand optical properties of organic molecules. In the present investi-gation, 3-acetyl-2-methyl-4-phenylquinolin-1-ium chloride3A4MPQ has grown by slow evaporation solution growth methodand the structural, optical, thermal, mechanical; luminescenceand etching properties of the title compound have analyzed whichhas closely related to optoelectronic applications.

Fig. 2a. Grown crystal of 3A4MPQ.

Fig. 2b. Molecular structure of 3A4MPQ.

Experiment

Synthesis

The material has synthesized by following the method of Kiranet al. [13]. A mixture of 2-aminobenzophenone (0.01 M), acetylacetone (0.01 M) and a catalytic amount of concentrated HCl haveirradiated under 240 W for about 5 min. The resultant solid havefiltered, dried and purified by column chromatography using a1:1 mixture of ethyl acetate and petroleum ether, and recrystal-lized using ethanol.

Solubility

The solubility of 3A4MPQ has determined in the temperaturerange 30–50 �C. This process has repeated for every 5 �C using anultra cryostat with accuracy of ±0.01 �C. The concentration of thesolute has determined gravimetrically. The solubility for 30 �Chas determined by dissolving 3A4MPQ salt in 100 ml of ethanol ta-ken in an air tight container maintained at the temperature withcontinuous stirring of the solution. In the saturated solution, 5 mlhas pipetted out and then poured into a Petridish of known weight.The amount of the salt present in 5 ml of the solution has mea-sured by subtracting the empty beaker’s weight. From this, amountof the salt present in 100 ml of the solution have found out. In thesame way, the amount of salt dissolved in 100 ml at 35, 40, 45,50 �C has determined. Fig. 1 shows the solubility curve of3A4MPQ salt. From the solubility diagram, (Fig. 1) it has observedthat the solubility of the material increases with an increase intemperature, exhibiting a high solubility gradient and positivecoefficient.

Crystal growth

The single crystal of 3A4MPQ has grown using slow evaporationtechnique at ambient temperature. The Purified salt has used forgrowing bulk single crystals. A saturated solution has prepared atroom temperature by using ethanol as a solvent. The temperatureof the solution has risen by 5 �C above the room temperature in or-der to obtain a homogeneous solution in ethanol. The filtered solu-tion has risen by 3 �C above the room temperature. Defect free seedcrystal has introduced into the mother solution. The beakercontaining the saturated solution has optimally covered withperforated sheet for controlled evaporation of the solvent. A

transparent single crystal of size 4 mm � 4 mm � 2 mm haveobtained in a period of 10 days. The photographs of the as grown3A4MPQ crystal have shown in Fig. 2a respectively.

Characterization studies

The single crystal X-ray diffraction (XRD) analysis of 3A4MPQcrystal have carried out using ENRAF NONIUS X-ray diffractometerand its unit cell dimensions, and morphology has determined. Thepurity and crystalline nature of 3A4MPQ compound has confirmed

Fig. 4. Powder XRD pattern of 3A4MPQ.

80 M. Nirosha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 78–84

by recording powder X-ray diffraction pattern using a REICH SIEF-ERT X-ray diffractometer employing Cu Ka (1.54058 Å) in therange of 10–70� in the steps of 0.02�. The FTIR analysis of thegrown crystal has recorded in the range 400–4000 cm�1. It has car-ried out using FT-IR 4100 type-A spectrophotometer employingKBr pellet technique at room temperature. The UV–vis spectrumhas recorded for the grown crystal using ELICO SL 218 double beamUV–vis spectrophotometer, in the range 190–1100 nm. The ther-mal analyses have carried out using a SDT Q600 V8 apparatus ata heating rate of 10 �C/min in the temperature range 30–1000 �Cat nitrogen atmosphere. The PL spectrum have recorded using Jo-bin Yvon-Spex spectrofluorometer (Fluorolog version 3: ModelFL3-11) at room temperature; 450 W high pressure xenon lampacts as an excitation source. Etch patterns have analyzed using aCarl Zeiss metallurgical microscope (Axios kop 40 MAT) in thereflection mode. Micro hardness studies have carried out withMututoyo MH-112 micro hardness tester using Vickers diamondpyramidal indenter attached to a metallurgical microscope.

Results and discussion

Single crystal X-ray diffraction

The grown crystals have subjected to single crystal X-ray dif-fractometer with Moka radiation of wavelength k = 0.71073 Å isto determine the unit cell dimensions and morphology. The latticeparameters are a = 9.4056 Å, b = 8.5787 Å and c = 18.2538 Å withspace group symmetry P21/c. From the data, it has observed thatit belongs to monoclinic system. The observed lattice parametershave found to be in good agreement with the reported values[13]. The morphology of the grown crystal as shown in Fig. 3

Powder X-ray diffraction

The well defined Bragg’s peaks at particular 2 theta angles in thepowder XRD spectrum have shown in Fig. 4. The peaks have in-dexed using APPLEMAN program from the 2 theta values.

FTIR spectral analysis

FT-IR spectroscopy has used to identify the functional groups ofthe synthesized compound and hence to elucidate its molecularstructure [14]. The recorded FTIR spectrum as shown in Fig. 5.The peak observed at 1701.22 cm�1 is due to the presence ofC@O of the compound. The presence of a methyl group (CH3) hasconfirmed by the peak observed at 1390.68 cm�1. The peak ob-served at 1556.55 cm�1 confirms the presence of secondary amineNAH vibration. The presence of CAC bond has confirmed by thepeak observed at 962.48 cm�1. The peak observed at1838.16 cm�1 1917.24 cm�1, and 1973.18 cm�1 are due to the

Fig. 3. Morphology diagram of 3A4MPQ.

presence of CAH bond present in the 1st ring (Fig. 2b) of the com-pound. The peak observed at 536.21 cm�1, 709.80 cm�1,767.67 cm�1 and 833.25 cm�1 is due to the presence of the CAHbond present in the second ring of the compound. The peak ob-served at 3049.46 cm�1 is due to the presence of CAH bond presentin the 3rd ring of the compound.

UV–visible spectrum

The UV–vis–NIR spectrum gives information about the struc-ture of the molecule. The absorption of UV and visible light in-volves promotion of the electron in the r and p orbital from theground state to higher states [15]. The absorbance spectrum hasrecorded for the 2 mm thickness crystal in the range 190–1100 nm and it as shown in Fig. 6. The transmittance is high inthe visible region of the spectrum. There is no significant absorp-tion in the range 372–1100 nm. The cut-off wavelength is371 nm. The peak observed at 371 nm is due to p–p* transitioncontributed by the quinoline backbone. The low cut-off wave-length and greater transparency in the visible region make it a suit-able material for optoelectronic applications [16]. The opticalabsorption coefficient (a) has calculated using the relation

a ¼ 2:3026ð1=TÞ=t ð1Þ

where T is the transmittance and t, is the thickness of the crystal.Optical band gap value has calculated from the transmission spec-tra, and optical absorption coefficient (a) near the absorption edgehas given by

Hma ¼ Aðhm� EgÞ1=2 ð2Þ

where A is a constant, Eg is the optical band gap, h is the Planck’sconstant and t the frequency of the incident photons. The bandgap can be calculated by plotting (aht)1/2 vs. ht as shown in Fig. 7and extrapolating the linear portion near the onset of the absorp-tion edge to the energy axis. From the figure, the value of bandgap value has found to be 2.72 eV. The lower band gap of the titlematerial makes these compounds interesting for solar cell and pho-tovoltaic devices [17,18].

TG/DTA studies

Thermogravimetric and Differential thermal analyses giveinformation regarding phase transition, water of crystallizationand different stages of decomposition of the crystal [19–20]. Therespective TGA/DTA trace for 3A4MPQ crystal has shown inFig. 8. TGA curve precisely shows there is no weight loss up to228.63 �C. The Thermogram spectrum reveals that the significant

50010001500200030004000

-25

0

25

50

75

100

%T

3442.9

4

3381.2

1

3049.4

6

1973.1

8

1917.2

4

1838.1

6

1701.2

2

1556.5

5

1479.4

0

1390.6

8

1354.0

3

1195.8

7

1159.2

2

1126.4

3

1078.2

1

1028.0

6

962.4

8

833.2

5

767.6

7

709.8

0

536.2

1

Fig. 5. FTIR spectrum of 3A4MPQ.

Fig. 6. UV–visible absorbance spectrum of 3A4MPQ.

Fig. 7. Plot of ht vs. (aht)½.

Fig. 8. Photoluminescence spectrum of 3A4MPQ.

Fig. 9. TG/DTA spectrum of 3A4MPQ.

M. Nirosha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 78–84 81

weight loss starts at 228.63 �C, and it continues up to 250 �C. Thesecond stage of weight loss starts at 343.30 �C, and it continuesup to 379.57 �C. This is due to the loss of ionic Cl� along with themethyl group of acetyl function in the molecule. In the DTA spec-trum, an exothermic peak observed around 156.21 �C correspondsto the melting temperature of the material. From the results ofthermal analysis, it has established that no transformation andweight loss observed before 228 �C. Hence the material can beexploited for any suitable applications up to 228 �C. The resulting

DSC trace (Fig. 9) shows a sharp endothermic peak at 156 �C repre-sents the melting point of the crystal. The sharpness of the peakindicates the good degree of crystalline perfection of the sample.

Photoluminescence

The Photoluminescence spectrum provides information of dif-ferent energy states available between the valence band and con-duction band responsible for radiative recombination [21]. The PLintensity is most probably dependent on the crystallinity and

Fig. 10. DSC curve of 3A4MPQ.

82 M. Nirosha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 78–84

structural perfection of the grown crystal. Fig. 10 represents the PLspectrum of 3A4MPQ single crystal. The sample has excited at370 nm. The emission spectrum has recorded between 380 and650 nm. There are two categories of luminescent peaks in the spec-tra. One category, ranging from 380 to 420 nm, has located in therange of ultraviolet and violet light. The other consists of blueluminescence ranging from 450 to 475 nm. The PL emission ofthe title material may find their applications in ultraviolet and blueorganic light emitting diodes [22,23].

(a) Without etching (b

(c) Etching 60s

Fig. 11. (a) Without etching, (b) 45

Etching

The microstructure has revealed by a surface treatment usingan appropriate chemical reagent in a procedure termed etching[24]. Chemical etching is a very simple and elegant technique to re-veal the crystal defects and the crystal growth mechanism. Etchingtechnique helps to develop some features such as growth stria-tions, etch spirals; rectangular etch pits etc., on the crystal surface.The etching behavior of 3A4MPQ crystal have carried out by usingdeionized water as an etchant at room temperature for etchingtimes of 30 s, 45 s and 60 s. The etch pits have observed at roomtemperature for varying times. The specimen surface must firstbe ground and polished to a smooth and mirror like finish. Thishas accomplished by using successively finer abrasive papers andpowders. Etching studies has performed on as-grown (01-1) face.Surface layer has removed by means of etching a fresh surfaceappeared gave clear etch pits. Fig. 11(a) shows the surface of thecrystal before etching. It is clear from the image that the growncrystal has a smooth surface. When etched with water for 30 s,the pits have not observed. Further etching for 45 s produced agreater number of small sized triangular pits as shown inFig. 11(b) When the etched with water for 60 s, the patternremains the same, but the size of the etch pits has slightlyincreased which as shown in Fig. 11(c). From the etching studies,it reveals that the observed etch pits are due to layer growth andhence confirms the two-dimensional nucleation mechanism with

) etching 45s

s etching and (c) 60 s etching.

Fig. 13. Plot of log p vs log d.

Fig. 14. Load vs. stiffness constant.

M. Nirosha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 78–84 83

fewer dislocations [25]. The calculated etch pit density value hasfound to be 1.25 � 103 cm�2. The generation of dislocations hasstrongly correlated with the formation of inclusions in the crystals[26,27]. These inclusions are due to variation in supersaturationduring the growth, non-uniform growth rates etc., are responsiblefor the formation of inclusions.

Micro hardness studies

Hardness is a measure of resistance to plastic deformation. Thehardness of the material plays a significant role in device fabrica-tion. The Hardness of the crystal carries information about thecrystal structure, yield strength and molecular bindings of thematerial. Micro hardness studies have applied to understand withplasticity of the substance [28]. Experiment has carried out withMututoyo MH-112 micro hardness tester using Vickers diamondpyramidal indenter attached to a metallurgical microscope. Crystalwith flat and smooth faces free from any defects has chosen for thestatic indentation tests. The indentations have made at room tem-perature with a constant indentation time of 10 s. Vickers microh-ardness test has carried out on (01-1) face of the grown crystal. Thesurface has gently polished with water. Then the polished crystalhas correctly mounted on the base of the microscope and indentedgently by applying loads 10–50 g with a dwell time of 10 s. At leastfive indentations have made on sample for each load. The indentedsurface has examined under the microscope. The lengths of the twodiagonals of the indentations have measured by a calibratedmicrometer attached to the eyepiece of the microscope afterunloading. The average diagonal lengths measured at each time.The Vickers microhardness number of the crystal Hv has calculatedusing the formula.

Hv ¼ 1:8544P

d2 ð3Þ

where P is the load applied, and d is the mean diagonal length of theindentation. Fig. 12 shows the plot between load (P) and (Hv) of3A4MPQ single crystal. It is evident from the plot that the microh-ardness value increases with the load shows the reverse indentationsize effect [29]. At higher loads above 50 g measurement has not ta-ken further since cracks begin to occur. It is due to the release ofinternal stresses generated locally by indentation [30]. Hence thematerial can be used for the device below the applied load of50 g. The Meyers index number has calculated from Meyer’s law[31] which gives the relation between the load and indentationdiagonal length.

P ¼ kdn ð4Þ

Fig. 12. Plot of Load vs. Hv.

log p ¼ log kþ n log d ð5Þ

where k is the material constant and n, is the Meyer’s index. Theplot of log p against log d is a straight line, and it as shown inFig. 13. The slope of the graph gives n, and it has found to be 2.41respectively. Vickers hardness value should increase with the in-crease of P if n > 2 and decrease in n < 2. The obtained value agreeswell with the experimental values. According to Onitsch [32] andHanneman [33], n should lie between 1 and 1.6 for harder materialsand above 1.6 for softer materials. Thus, 3M4APQ crystal belongs tosoft material category.

The elastic stiffness constant (C11) for different loads calculatedusing Wooster’s empirical formula C11 = Hv

7/4. It gives an ideaabout the tightness of bonding between neighboring atoms [34].Fig. 14 shows the stiffness constant with load, stiffness constant in-creases with increasing load.

Conclusions

Single crystals of 3A4MPQ have grown by slow evaporationsolution growth technique. The lattice parameters have found bysingle crystal X-ray diffraction technique. The FT-IR spectrum re-veals the various functional groups present in the grown crystal.

84 M. Nirosha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 78–84

The optical absorbance spectrum reveals that the crystal has wideoptical window from 372 to 1100 nm. The crystal is transparent inthe visible region of the spectrum. The PL spectrum shows the blueemission in the crystal. The Vickers microhardness has calculatedin order to understand the mechanical stability of the growncrystals. Hardness measurement shows that the hardness of thesample increases with increasing load. From the TGA and DTAcurves, it has analyzed that the sample is highly stable up to228 �C, and its melting point has found to be 156 �C. The crystalperfections and quality have identified by using the etchingstudies.

Acknowledgement

The author acknowledges SAIF IIT madras for proving the S-XRDfacility. The authors are also thankful to VIT University for provid-ing excellent research facilities.

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