Synthesis and Preparation of Poly (P-Phenylene Vinylene)
Thin Film and structural Characterizations
S. Sakthivel, A. Boopathi, M. Iswarya and A. Elakkiya
Assistant Prof. of Physics & Research Scholar, Students Thin Film Physics and Nano Science Laboratory
PG and Research Department of Physics,
Rajah Serfoji Govt. College, Thanjavur, Tamilnadu, INDIA.
email:sakthivel.sunmugam@yahoo.com, Boopathi.annamalai@yahoo.co.in.
(Received on: October 15, 2015)
ABSTRACT
The organic materials are very important in development of organic light emitting diodes (OLED) in electronic industry. The organic material is based in conjugated polymers of phenylene and vinylene functional group polymers of Poly Phenylene Vinylene (PPV) in thin film form. We have report here the synthesis of PPV precursor polymer in solution-processable route of wessling method. The synthesised PPV precursor polymer converting to PPV conjugated polymer in coating of glass substrate by using one of the thin film preparation method of simple cost effective spin coating technique the coated thin film were annealing to 3500C for twenty four hours this time period taken for complete conversion of PPV precursor to PPV conjugated polymer its conductive state. Then we have studied by the structural and vibrational spectroscopy and film optical and luminescence properties were studied in Ultra violet visible spectroscopy.
Keywords: OLEDs, conductive polymers, Poly Phenylene Vinylene (PPV), FTIR, XRD, PL study of PPV.
1. INTRODUCTION
Organic polymer LEDs has many advantages for the development of large area visible light emitting display. The OLEDs is fast response time and color tenability over the full visible range by control of the HOMO-LUMO state of band gap of the emissive layer1-2. There are
number of conjugated backbone structures have been used in OLEDs making process that’s materials such as PPV, Poly (P-phenylene) (PPP), Polythiophene (PTh) and Polyfluorene (PF) in this all materials individually differ color emissive range of OLED devices. The most promising and extensively studied group of polymer is a PPV and its derivatives in year 2013 (Taek ahn) synthesised and studied of new random copolymers of phenylene and alkoxy substituted phenylene vinylene of PPV and fabricated with emitting layer of light emitting devices emission maxima at 575nm, 565nm and 541 nm3-4. In fundamental studies of PPV
using film formation techniques such as solution processable such as casting, spin coating, layer by layer growth and Langmuir-Blodgett (LB) methods. The A. Marletta et al. results of synthesis route to yield PPV is allowed for thermal conversation is considerably less time period and at lower temperature than typical conversion procedures using the polymer precursor poly(xilidenotetrahydrothiophenium chloride) (PTHT) offers to tune the PPV properties as the PTHT chlorine counter ion may be replaced by dodecylbenzene sulfonic acid (DBS)5.
The pure PPV is insoluble polymer, intractable, infusible and therefore difficult to process. Solution processability is desirable as it allows polymeric materials to be solution cast as thin film for various applications. A general methodology to overcome this problem by wessling method (Wessling & Zimmerman, 1968; Wessling 1985) of solution processable polymer of soluble precursor synthesis route and potential drawback of the precursor route is the limited control over polydispersity and molecular weight of the resulting polymer6-8.
In this present work we have synthesis of PPV precursor polymer and prepare thin film PPV by direct conversion thermal heating at 3000C at precursor coated substrate at 120
minutes after prepared thin film sample were studied by structural and optical characterizations.
2. EXPERIMENTAL SECTIONS
2.1 Materials
α,α’,-dichloro-p-xylene (Assay98%, C6H6Cl2, MW: 175.06), Tetrahydrothiophene
(Assay 99%, C4H4S, MW: 88.17g/mol) were used as source materials from Aldrich. Double
distilled (DD) water was used as a solvent. Methanol (MeOH) and Sodium hydroxide (NaOH) analytical research grade obtained from Merck. All chemicals are used in this work as received.
2.2 Synthesis and Precursor Polymer PPV
The synthesis of precursor polymer route as follow the α,α’,-dichloro-p-xylene salt
methanolic solution of monomer of bis-sulfonium salt is induced by the addition of slightly less than 1 mol equivalent of aqueous sodium hydroxide at 0-50C. If more base is used, the
resulting polymer solution become brightly colored owing to patial base-induced elimination of the sulfonio groups. The terminated solution was neutralized by using dilute hydrochloric acid. The neutralized solution almost colorless solutions of precursor polymer obtained then dialyzed against distilled water to remove impurities having low molecular weight polymers9.
2.3 Preparation of PPV Thin film
The precursor polymer is converted into PPV by using drop costing technique at different molarities solutions in different thickness sample have prepared in thermal conversion method of standard temperature of 3000C for 120 minutes under this conditions the
by-products of the elimination (tetrahydrothiophene and hydrogen chloride) escape easily.
2.4 Characterizations of PPV Thin film
The vibrational properties of the PPV thin film were analyzed by Fourier transform infrared spectroscopy (FTIR) Perkin Elmer make model spectrum RXI spectroscopy in the wave number range of 400-4000 Cm-1. The thin film thicknesses were measured by using
direct measurement technique of Surface Profilometer (SJ Mitutoyo 301). The optical absorption of samples with varies thickness thin film PPV were recorded in the wavelength range of 300-800 nm using Lambda 35 UV-Vis spectrometer. The photoluminescence spectra of PPV thin film sample were analysed using photoluminescence spectrometer in the wavelength range of 300-800 nm.
3. RESULTS AND DISCUSSION
3.1 FTIR Spectroscopy Analysis
The FTIR transmittances spectra of syntheses precursor polymer (A) and thermally converted PPV Thin film (B) as shown in figure 1. The C-Cl vibrational frequencies are located around 668 cm-1 in sample A and this peak shifted at 695 cm-1 its very less intensity this means
the chlorine molecules reduces conversation of PPV, and the aliphatic transmission of just below 3035 cm-1 and 1470 cm-1 this means in our sample fully converted PPV8. The thermal
converted PPV in between 590 cm-1 to 695 cm-1 there is no any peaks at present here the
position indicating that complete elimination of sulphur from film were heated 3000C9. The
sample B show bands 1505 cm-1 and 1602 cm-1 are due to stretching vibration of C=C aromatic
and also the bands appeared between 1057 cm-1 and 1306 cm-1 that belongs to the bending
vibrations of C-H aromatic. The absorption band around 530 cm-1 was attributed to the
phenylene out of plane ring bending. The bands at 837 cm-1 and 1505 cm-1 were assigned to
Fig 1. FTIR Spectrum of A) PPV Precursor Polymer B) Fig 2. Thickness of PPV Thin films PPV Thin film
3.2 Thickness Measurements
The figure 2 shown as thickness of the PPV thin film were coated in changing parameter of sol-gel spin coater at different spinning speed of 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm respectively, the name of sample were notated at after the coating and thermal conversation process. The name of sample were a, b, c, and d thickness in nano meter range of 132nm, 120nm, 105nm, 74nm, and 68nm we absorbed that the rotation of after 3000 rpm range of 3500 rpm and 4000 rpm we get thickness variation higher than up to 3000 rpm from 2000 rpm.
3.3 UV-Vis Absorption Spectroscopy Analysis
The figure 3 shown that UV-Vis absorption spectra of different thickness of PPV thin films. This figure clearly indicate that thickness variations of thin films is directly professional for absorption of UV to Visible range of light, we notated this phenomena higher thickness film have a higher absorption intensity of 1.3 (a.u) and lower thickness thin film absorption degreased around 0.7 (a.u). The whole absorption peaks with maximum of all the PPV films were around 500 nm preparation at the constant heating of 3000C this proves that the precursor
PPV was successfully converted into the conjugated PPV under the selection of temperature condition11. The PPV thin films at good transparency above 800 nm range.
3.4 Photoluminescence Spectroscopy Analysis
The figure 4 shows the photo-luminescence spectra of different thickness of PPV thin films of single layer structure and the colour of film as orange mixes yellow thin layer film we obtained. The PL spectrum shows an emission peaks around at above 550 nm range8, PL
spectrum intensity sharpness is reduced by dependant of thickness variation however the second emission also present in this samples the value were notated by the figure. This PL emission peaks is a strong intensity and the expected red shift. In previous report cleared that the intensity decreases as the conjugation length increase at different temperature so we have here conclude the conjugation length is controlled the PPV structure.
Fig 4. PL Spectrum of PPV Thin films
4. CONCLUSION
The conclusion of this paper we have synthesized PPV precursor solution and preparation of luminescence polymer PPV thin film at a different thickness by varies spinning speed of solution based spin coating technique in constant temperature of 3000C. The
vibrational spectroscopy clearly showed mainly important peaks and band structures are present confirmations. The thickness variations of PPV film of 132-68 nm are easily achieved by spin coating method and the optical properties of films are clearly studied in UV-Vis and PL spectroscopy technique, the absorption and transmissions at different wavelength ranges depend on thickness of films. The PL spectra intensity sharpness depend the thickness of the PPV films.
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