Accepted Manuscript Growth and characterization of organic NLO material: Clobetasol Propionate R. Purusothaman, P. Rajesh, P. Ramasamy PII: DOI: Reference:

S1386-1425(15)00310-8 http://dx.doi.org/10.1016/j.saa.2015.03.014 SAA 13428

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

3 October 2014 13 February 2015 1 March 2015

Please cite this article as: R. Purusothaman, P. Rajesh, P. Ramasamy, Growth and characterization of organic NLO material: Clobetasol Propionate, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.03.014

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Growth and characterization of organic NLO material: Clobetasol Propionate R.Purusothaman, P.Rajesh* and P.Ramasamy. Department of Physics, SSN college of Engineering, Kalavakkam- 603 110. Abstract Single crystals of clobetasol propionate (CP) have been grown by slow evaporation solution technique using mixed solvent of methanol-acetone. The grown crystals were subjected to single crystal X-ray diffraction analysis to confirm their lattice parameter and space group. The powder X-ray diffraction pattern of the grown CP has been indexed. Thermal analysis was performed to study the thermal stability of the grown crystals. Photoluminescence spectrum shows broad emission peak observed at 421 nm. Nonlinear optical studies were carried out for the grown crystal and second harmonic generation (SHG) efficiency was found in the crystal. Keywords: Nonlinear optical crystals, Organic compounds, X-ray diffraction, Photoluminescence. PACS: 42.70.Mp, 61.66.Hq, 61.10.Nz, 78.55.-m.

*Corresponding author Tel:+91-9840522490. E-mail: [email protected]

1

1. Introduction Clobetasol propionate (CP) has recently attracted many researchers due to their potential application in nano-biotechnology, biomedical and paramedical fields. CP has the molecular formula C25H32CIFO5 and a molecular weight of 467. It is a white to cream-colored crystalline powder and insoluble in water. Recently, organic nonlinear optical crystals are playing vital role due to their potential application in optical switches, modulators, optical limiters, and optical data storage[1,2] and also they have greater optical susceptibilities, and higher optical thresholds for laser power compared to inorganic materials, as well as inherent ultrafast response time[3]. Organic compounds containing push–pull conjugation can present large optical second-order molecular polarizabilities and possess application in second-order nonlinear optical devices. Depolarization and intermolecular charge transfer effect of π-electrons in the molecules can cause large and fast nonlinear responses. By molecular engineering, it is possible to develop many organic crystals displaying better nonlinear optical properties than the inorganic materials, in particular for second harmonic generation (SHG) [4, 5]. The second harmonic generation properties of the materials require non-centrosymmetric crystal structure. It possesses parallel alignment of molecules, which results in high hyperpolarizability and large secondorder nonlinear susceptibilities for the crystals. In the case of centrosymmetric crystals, the even order nonlinear optical susceptibilities are zero in the electric dipole approximation [6, 7]. The crystal structure of CP has been already reported by Masayuki Haramura et.al. The crystal system belongs to monoclinic having unit cell parameters a=7.696 Å, b=14.6030 Å, c=10.4355 Å, β=95.739°, α=90°, γ =90° and space group P21. In the previous works, microparticulate based topical delivery system 2

of Clobetesol Propionate [8] and Stress degradation study [9] have been made. The purpose of the study was to develop a new topical delivery system in order to provide the prolonged release of clobetasol propionate and to reduce systematic absorption and side effects of the drug. The present work focused to grow the material as a crystal by slow evaporation method and investigates the properties towards spectroscopic point of view for NLO applications. Important spectral behaviours like photoluminescence, XRD and thermal behaviour of the crystal have been studied. 2. Materials and Methods 2.1 Crystal growth The starting material was commercially available CP salt and it is dissolved in the mixed solvent of methanol and acetone in the 1:1 ratio. The solvent evaporation technique was used to grow the single crystal of CP and its purity has been improved by recrystallizing two times. Using recrystallized material saturated solution has been prepared and kept for evaporation. Transparent single crystals of CP of size upto 6x4x3 mm3 were obtained in the span of 4 days and the grown crystals are shown in Fig.1. 2.2. Characterization The single crystal X-ray diffraction studies of the crystals were carried out using Enraf-Nonious CAD4 diffractometer with MoKα (λ=0.717 Å) radiation. The powder X-ray diffraction analysis of CP was carried out using analytical X’pert power diffractmeter (Netherlands). The Kα radiations from a copper target (λ=1.5418 Å) was used. The CP crystal was ground into fine powder and powdered sample of CP was spread over a square centimeter area and placed in a beam of monochromatic X-rays. 3

The mass of powder was rotated about all possible axes. The sample was scanned over the range 10-80º at a rate of 2º/min. Thermal property of grown crystal was studied using PerkinElmer Diamond DTA/TGA analyzer at 10°C/min heating rate performed between 30°C and 500°C in the nitrogen atmosphere. The second harmonic generation efficiency was examined by Kurtz and Perry powder technique with reference to KDP. The existence of second harmonic generation (SHG) signal was observed using Nd:YAG laser with fundamental wavelength of 1064 nm. The PL spectrum was recorded with a Jobin Y VanSpexSpectrofluorometer (Fluorolog version-3. Model/FL3-11) at room tempearture.

3. Results and Discussion 3.1. Single crystal XRD From this measurement it is observed that the crystal belongs to monoclinic system in the space group P21 and the unit cell parameters are a=7.696 Å, b=14.6030 Å, c=10.4355 Å, β=95.739°, α=90°, γ =90°. These values agree well with the previously reported values [10]. 3.2. Powder XRD analysis Powder X-ray diffraction analysis has been carried out to confirm the crystallinity and also to identify phase purity of material. The powder X-ray diffraction pattern of CP crystal is shown in Fig.2. From the 2θ value the lattice spacing was obtained. The prominent peaks confirm the crystalline nature of the grown crystal. The powder XRD pattern of grown crystal has sharp peaks which indicate good crystalline nature of the crystal. All the observed reflection peaks were 4

well indexed using the 2θ software package. The diffraction pattern is identical with already reported results [8]. Table.1 shows the calculated d space values of the CP single crystal.

3.3. Thermal analysis Thermal Analysis (TA) is a group of techniques that study the properties of materials as they change with temperature. The observed TG-DTA curve is shown in Fig.3. The measurement indicates that the material exhibits two-stage weight loss, in first stage material the weight loss is upto 31% and in second stage remaining 69% weight loss was observed. It may be due to the decomposition of complex molecule present in the CP. For the DTA curve an endothermic peak is observed at 195˚C, which is corresponding to melting point of the material. The sharpness of the endothermic peak observed in DTA reveals good degree of crystallinity of the grown crystal. Hence it is concluded that CP crystals can be used for device application till 195˚C. The obtained result is in good agreement with the reported result [8]. 3.4. Kurtz powder technique for second harmonic generation test CP has been crystallized in a non-centrosymmetric space group; it should have tendency to exhibit second harmonic generation (SHG). The level of SHG response of a given material is inherently dependent on the molecular and supramolecular nature of the compound. The nature of the crystal packing, such as hydrogen bonds, local crystal-field effects and intermolecular interactions are highly influence in the SHG effect [11]. On a molecular scale, the extent of charge transfer (CT) across the NLO chromophore determines the level of SHG output, the greater the CT, the larger the 5

SHG output. The SHG was measured by Kurtz and Perry powder technique. The crystal was grounded into a fine powder and densely packed between two transparent glass slides. A Q switched Nd: YAG laser emitting a fundamental wavelength of 1064 nm (pulse width 8 ns) was allowed to strike the sample cell. The SHG output 532 nm was finally detected by the photomultiplier tube. The second harmonics signal, generated in the crystal was conformed to have the emission of green radiation by the crystal. The powdered material of potassium dihydrogen phosphate (KDP) was used in the same experiment as a reference material. The output power intensity was found to be 0.35 times that of KDP. 3.5. Photoluminescence The Photoluminescence (PL) spectrum provides information of different energy states available between the valence band and conduction band responsible for radiative recombination. The PL spectrum was recorded with a Jobin Y VanSpexSpectrofluorometer (Fluorolog version-3. Model/FL3-11). The recorded PL spectrum of CP crystal is shown in Fig.4 with the excitation wavelength of 244 nm. From the PL spectrum it is observed that, a broad emission peak at 421 nm is due to blue emission. The PL intensity is most probably dependent on the crystallinity and structural perfection of the grown crystal. The molecular structure of the CP is given below.

6

Normally this type of steroid compound has chromophores which are responsible for absorption in visible region. A broad emission is observed at 425 nm which is due to two chromophores present in the compounds, that is cyclohexadinenone moiety in ring A and carbonyl group at C20 [12] or it may be due to n-π* transition (both singlet – singlet and triplet- triplet) between carbonyl group of ketones in Clobetesol Propionate [13-14]. 4. Conclusion

Single crystal of CP has been grown by slow evaporation solution technique. The grown crystal belongs to the monoclinic system with space group P21. The powder XRD pattern confirms good crystalline nature of the grown crystal. The thermal analysis peak indicates CP is stable upto 195°C. From the Kurtz and Perry powder technique it is found that SHG efficiency is 0.35 times that of pure KDP crystal. PL emission is observed at 425 nm. Reference [1] J. Zyss, Molecular Nonlinear Optics: Materials, Physics and Devices, Academic Press, Boston, 1994. [2] R.W. Munn, C.N. Ironside, Principles and Applications of Nonlinear Optical Materials, Chapman & Hall, London, 1993. 7

[3] M. Samoc, A. Samoc, B. Luther-Davies, J. Opt. Soc. Am. B 15 (1998) 817-825.

[4] Huang Bingrong, Su Genbo, He Youping, J. Cryst. Growth 102 (1990) 762-764. [5] Sharada G. Prabhu, P. Mohan Rao, J. Cryst. Growth 210 (2000) 824-827. [6] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystal, Academic Press, New York, 1986.

[7] S. Sudhahar, M. Krishna Kumar, B.M. Sornamurthy, R. Mohan Kumar, Spectrochim. Acta. Part A 118 (2014) 929-937.

[8] Ulya Badilli, Tangul Sen, Nilufer Tarimci, AAPS PharmSciTech 12 (2011) 949957.

[9] M.C. Damle, A.R. Polawar, International Journal of PharmTech Research 6 (2014) 1914-1925.

[10] M. Haramura, A. Tanaka, T. Kimoto, N. Hirayana, Analytical Sciences 19 (2003) x37-x38.

[11] J.M. Cole, A.E. Goeta, J.A.K. Howard, G.J. Mclntyre, Acta Cryst. A B58 (2002) 690-700.

[12] J. Iqbal, A. Gupta, A. Husain, Arkivoc 9 (2006) 91-98.

[13] J.C. Dalton, N.J. Turro, Annu. Rev. Phys. Chem. 21 (1970) 499-560.

[14] S. Goswami, R. Saha, I. M. Steele, P. Dasgupta, A. Poddar, S. Kumar, Inorg. Chim. Acta. 410 (2014) 111-117.

8

Figure Captions Fig.1. As grown crystal of clobetasol propionate Fig.2. Indexed powder XRD pattern of the crystal Fig.3. Thermal behaviour of the grown crystal from TG-DTA Fig.4. Photoluminescence spectrum of the grown crystal

9

Fig.1. As grown crystal of clobetasol propionate

10

(110)

700

(100) (101)

600

(20-3) (122)

200

100

(23-3)

300

(10-1) (121) (23-1) (013)

400

(011)

Intensity (CPS)

500

0 0

10

20

30

40

50

60

70

2 (degree)

Fig.2. Indexed powder XRD pattern of the crystal

11

80

90

80 100

o

60

80

60 40 o

197 C 40 20 20

0

0 0

100

200

300

400

500

Temperature (°C)

Fig.3. Thermal behaviour of the grown crystal from TG-DTA

12

Weight (%)

Microvolt Endo Down(µV)

198 C

50000

425 nm 40000

Intensity(cps)

30000

20000

10000

0

250

300

350

400

450

500

wavelength (nm)

Fig.4. Photoluminescence Spectrum of the grown crystal

13

Table Caption

Table.1. The interplanar spacing value (d) for prominent peaks of powder XRD pattern of the grown crystal hkl value 2θ(degree) (011) (100) (110) (10-1) (121) (23-1) (013)

11°37' 11°47' 13°37' 16°57' 19°57' 23°27' 26°47'

interplanar spacing value (d) value (Å) 7.7215 7.5038 6.4973 5.2263 4.4313 3.790 3.3256

14

Graphical abstract

15

Highlights 

A organic crystal clobetasol propionate has been grown with size upto 6x 4x3 mm3



It emits green radiation at 532 nm



It is thermally stable up to 195 oC



Photoluminescence observed at 421 nm indicates the blue emission.

16