Optical and Mechanical Studies of 4-Chloro-3-Methylphenol Single Crystal

Optical and Mechanical Studies of 4-Chloro-3-Methylphenol Single Crystal

A. Syed Mohammed Mujaheer1*, Foize Ahmed1, A. Sarbudeen2, M. Gulam Mohammed 1

1 P.G. and Research Department of Physics, The New College, Chennai-14, India

2 Department of Physics, Aalim Muhammed Salegh Polytechnic College, Chennai – 55, India

Abstract- Single crystal of 4-Chloro-3-Methylphenol, an organic non linear optical material was grown from aqueous solution by low temperature solution growth technique with ethanol as a solvent. Good optical quality single crystal of dimensions 15 x 5 x 2 mm3 was harvested in a period of three weeks. The crystal system was confirmed from single crystal X-ray diffraction analysis. FTIR spectral analysis reveals the presence of functional groups present in the grown crystal. The optical behaviour of 4-Chloro-3-Methylphenol crystal was identified from UV-vis-NIR spectrum and the cut-off wavelength was found . Microhardness studies were carried out using Vickers pyramidal indentation method shows that the grown crystal belongs to soft material.

Key words: Xray diffraction,FTIR ,UV analysis, microhardness studies

I INTRODUCTION

The nonlinear optical (NLO) materials capable of generating second harmonic have received a great deal of attention due to their commercial importance in the field of optical communications,signal processing ,sensing and instrumentation [1]. The requirement of non- centrosymmtry for SHG has been sucessfully designed in diffrent organic systems using a number of strategies.the most obvious is the use of a single enantiomer of a chiral component,which guarantees crystallization in an acentric space group [2]. In the last several years, organic NLO crystals have attracted much attention because of their superior properties,such as large susceptibility,faster responce than their inorganic counterparts and the capablity of designing on the molecular level. The organic compounds with electron sufficient (donor) and electron deficient (acceptor) counterparts, provide the asymmetric charge distribution in the electron system and shows large non-linear optical responses. Organic nonlinear optical materials may be far superior to their inorganic counter parts, owing to the irrelatively high and faster nonlinearities [3,4].Therefore ,presently there is a need to produce high efficient NLO materials capable of generating blue light by second harmonic generation[5,6]. Crystal of 4-Chloro-3-Methylphenol (4C3MP) is a known organic material, it has a wide range of application. Since there is no report available on the growth of 4C3MP. We have reported the growth of 4C3MP crystal by slow evaporation technique using ethanol as solvent. The grown crystal were subjected to single crystal XRD, optical and mechanical studies. The results of the XRD studies which shows that 4C3MP belongs to monoclinic crystal system and space

group P21. The optical behaviour of 4C3MP grown crystal was identified from UV-vis-NIR spectrum and the cut-off wavelength was determined. Microhardness studies were carried out using Vickers pyramidal indentation method shows that the grown crystal belongs to soft catagory.

II MATERIAL SYNTHESIS

The title compound 4-Chloro-3-Methylphenol was synthesised by dissolving C7H7ClO in ethanol. The aqueous solution was stirred for 4h and after stirring, the supersaturated solution was filtered with whatmann filter paper and kept in the dust free atmosphere. The saturated solution was allowed to dry at room temperature by the slow evaporation method. After a period of three weeks, optically transparent and defect free crystal was obtained with the dimensions of 15 x 5 x 2 mm3. The photograph of grown crystal was shown in Figure1.

Figure 1. Photograph of an grown 4C3MP crystal.

III RESULTS AND DISCUSSION

1. Single crystal XRD

   The grown crystals were subjected to single crystal X-ray diffraction using ENRAF NONIUS CAD-4 single-crystal X-ray diffract meter with MoK radiation ( = 0.7170 Ã…) to determine the unit cell dimensions. The pure crystal is found to be crystallized in the monoclinic system with space group P21. The cell parameters are listed in Table 1.

   Table 1 .Unit cell parameters

   Lattice parameters of 4-Chloro-3-	Crystal data
   Methylphenol
   	C7H7ClO
   Molecular Formula	Monoclinic System
   System group	P 21
   Space group	10.6998 (4) Ã…
   a	14.2926 (5) Ã…
   b	8.7105 (3) Ã…
   c	900
   	91.1520
   	900
   	1331.81(8) Ã…3
   Cell volume(V)

2. OPTICAL ABSORPTION STUDIES

   The optical absorption spectrum of the grown crystals was recorded in the range 200-800 nm and the absorption spectrum is shown in Figure 2. From the UV absorption spectrum, it was found that there is very low absorbance in the entire visible region. Excellent optical transparency with the lower cut-off wavelength at 283 nm makes it as a potential material for device fabrication.

   cut-off wavelength = 283nm

   3.0

   2.5

   Absorbance

   2.0

   1.5

   1.0

   0.5

   0.0

   300 400 500 600 700

   Wavelength (nm)

   Figure 2. UV-VIS-NIR spectrum of 4C3MP single crystal

   The optical band gap energy (Eg) was calculated using the relation

3. FTIR ANALYSIS

120

115

Transmittance (%)

110

105

100

95

90

85

80

75

4000 3500 3000 2500 2000 1500 1000 500

Wavelength (cm-1)

Figure 4. FTIR spectrum of 4C3MP crystal

The FTIR spectra of 4C3MP crystal was recorded in the range of 400-4000 cm-1.The OH group gives rise to three vibrations namely stretching, in-plane bending and out-of-plane bending vibrations. Hydroxyl group in the associated form absorbs at 35003300 cm-1, the value of frequency shift in phenols derivatives depends on the strength of the H bonds and also the type of association. The weaker CH stretching modes are generally superimposed upon the broad O H band due to intermolecular hydrogen bridge. The visual inspection of observed spectrum in Figure. 4 of 4C3MP of validate the above facts. Phenols without bulky ortho groups, whether in concentrated solution or as solids or in the pure liquid phase, have a broad absorption at 34003230 cm-1 [7]. Accordingly, in the present study the OH stretching vibration is observed at 3280.73 cm-1 in the FTIR spectrum

, which is due to no bulky ortho groups. The frequency due

to OH in-plane bending vibration in phenols, in general lies in the region of 11501250 cm-1 . The very strong FTIR band at 1324.55 cm-1 of 4C3MP are attributed to this vibration. For the associated molecule the OH out-of- plane bending mode lies in the region 572728 cm-1 [8]. In

A(h Eg

h

)1/ 2

both the intermolecular associations, the frequency is at a

higher value than in free OH. The OH torsional vibration is very anharmonic and hence it is difficult to reproduce

Where, h-incident photon energy, – absorption coefficient, Eg optical band gap. The plot of variation of (h)2versus h yields the band gap energy of 4.28eV for the grown 4C3MP crystal and it was depicted in figure 3.

80

this frequency with a harmonic approach. In our title molecule, the FTIR bands at 457 cm-1 are assigned to OH out-of-plane bending vibrations. CO group vibration The most important contribution to CO stretching modes appeared at 1239 cm-1. These modes can be described as

h)2(eV/m)2

600

400

200

Eg = 4.28 eV

coupled vibrations, involving main contributions from the CO stretch along with aromatic ring vibration [9]. The C O out-of-plane vibrations have an important contribution to.

0

4.0 4.1 4.2 4.3 4.4 4.5

h eV)

Figure 3. Plot of (h)2 versus photon energy for 4C3MP

IV VICKERS MICRO HARDNESS TEST

Measurement of hardness is a useful non destructive testing method used to determine the applicability of the crystal. Microhardness study was carried out on 4C3MP single crystal lusing a Vickers microhardness tester fitted with a Vickers diamond pyramidal indenter in order to evaluate its mechanical stability.

140

120

Hv (kg/mm2)

100

80

60

40

20

0 20 40 60 80 100

5000

Stiffness constant

4000

3000

2000

1000

0

0 20 40 60 80 100

Load P (g)

Load P (g)

Figure 5. Variation of load with vickers hardness number

The static indentations were made at room temperature with a constant indentation time of 5 s for all indentations. A cut and polished sample of 4C3MP was used for the study. The indentation were made by varying the load from 5 to 100 g at room temperature. The Vickers Microhardness number of the title crystal was calculated using the relation,

= 1.8544 (2) (kg/mm2)

Where,Hv is the Vickers hardness number, P is the applied load and d is the average diagonal length of the

indentation mark.

Plots between hardness number and load for 4C3MP single crystals at room temperature is depicted in Figure 5. It is clear that the microhardness number increases with increasing load, which is in agreement with the reverse indentation size effect (ISE) [10]. The relation connecting the applied load and diagonal length d of the indenter is given by Meyers law P =ad n [ 11], where the exponent n called as the Meyer number, is the measure of the Indentation Size Effect (ISE) and a, is the constant d is chordal diameter (diameter of the indentation). For the normal ISE behavior, the exponent n < 2.When n > 2, there is the reverse ISE behaviour. When n = 2, the hardness is independent of the applied test load, and is given by Kicks law [12].

Plots obtained between log(P) and log(d) for 4C3MP single crystal at room temperature is a straight line and is shown in Figure. 6.The value of n obtained for 4C3MP single crystal using linear fit is found to be 1.82 respectively. This is also in good agreement with RISE [10]. On careful observations made on various materials, Onitsch and Hanneman [13] pointed out that n lies between 1 and 1.6 for hard materials, and if it is more than 1.6 for soft materials.

An elastic stiffness constant or simply an elastic constant measures how hard a solid is. An elastic stiffness constant (C11) for the title compounds were calculated using the Woosters empirical formula C11 = Hv7/4. The plots of stiffness constant versus load P are shown in Figure 7. The trend of stiffness constant graph is similar to hardness number graph which gives an idea about tightness of bonding between neighbouring atoms [14].

40

38

36

34

log d

32

30

28

26

24

22

20

Figure 7 Plot of load P versus Stiffness constant

V CONCLUSION

Optically good quality single crystal of 4C3MP was grown by slow evaporation technique using a ethanol as a solvent

. the finding are concluded as fallows, Single crystal X-ray analysis confirms that the crystal belong to the monoclinic system with space group P21 , and lattice parameters a=10.6998Ã…, b=14.2926 Ã…, c=8.7105Ã… and = ==90Ã….

.FTIR spectral analysis confirms the presence of functional groups. The cut off wavelength for the 4C3MP crystal is about 283 nm and the band gap was found to be 4.28 eV from the UV-Vis analysis. Mechanical hardness studies reveal that Vickers hardness number decreases as the load increases and work hardening coefficient was found to be

1.82 and it reveals that the grown crystal belongs to soft material.

VI ACKNOWLEDGEMENT

The authors are deeply indebted to the Management and Department of Physics, The New College, Chennai, for providing the conductive environment to do my research work.

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0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

log P

Figure 6 Plot of log P versus log d