Ph.D PUBLIC VIVA-VOCE

Ms. U. Reeta Felscia (F9432) Research Scholar

Department of Physics and Research Centre

Lady Doak College, Madurai - 625 002

will defend her Ph.D Thesis entitled

“Theoretical and Experimental Investigations of Pyrene and its

Derivatives for Optical Applications”

at the Public Viva-Voce Examination on

Date : 03.06.2021

Time : 11:00 AM

Online Platform: Microsoft Teams

Link to Join :

External Examiner

Prof. E. James Jebaseelan Samuel, Senior Professor of Physics,

VIT University, Vellore.

All are Invited

Research Supervisor

Dr. Beulah J.M. Rajkumar

Associate Professor and Head(Rtd),

Dept. of Physics & Research Centre

Lady Doak College, Madurai.

Joint Supervisor

Dr. M.Briget Mary

Associate Professor and Head (Rtd),

Dept. of Physics & Research Centre

Lady Doak College, Madurai.

Head of the Department

Dr. R.Nimma Elizabeth

Associate Professor and Head

Dept. of Physics & Research Centre

Lady Doak College, Madurai.

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THEORETICAL AND EXPERIMENTAL INVESTIGATIONS OF

PYRENE AND ITS DERIVATIVES FOR OPTICAL APPLICATIONS

Synopsis submitted to Madurai Kamaraj University

in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY IN PHYSICS

By

REETA FELSCIA U

Reg No F9432

Supervisor

Dr. BEULAH J M RAJKUMAR

Co-Supervisor

Dr. M.BRIGET MARY

Department of Physics and Research Centre

Lady Doak College

Madurai 625002

MADURAI KAMARAJ UNIVERSITY

(University with Potential for Excellence)

Madurai-625021

Tamil Nadu, India

AUGUST 2020

1

Organic materials are steadily replacing conventional silicon based electronic devices due

to their remarkable optical, electrical, photo physical and charge transport properties.

Organic molecules have been used to fabricate electronic materials ever since organic

semiconductors were first discovered in the 1950s. Even today, researchers and engineers

continue to be attracted to organic materials for the design and fabrication of novel opto-

electronic devices.

Polycyclic aromatic hydrocarbons (PAHs) are one of the most important classes of organic

compounds that have been studied for application in this area. They are made up of laterally

fused benzene rings, which forms a planar structure. Due to the delocalization of π

electrons, these molecules exhibit a highly stable configuration. As of now, several studies

have been carried out with linear acenes due to their efficient device performance. Larger

acenes are expected to show superior electronic properties, but they are also highly unstable

and are known to cause photodegradation and oxidation. In 2014, L.Zhang et.al have

reported that the use of nonlinear acene systems reduce these negative effect substantially.

Therefore, the present research work attempts to overcome these problems by using two-

dimensional (2D) nonlinear acenes.

Development of computational techniques reduce time consuming and cost-intensive

experimentation processes and avoids the possibility of synthesising toxic materials as by-

products, which could adversely affect the environment. The advancement in

computational sciences in the 20th century led to the development of computational

chemistry leading to molecular modelling and molecular dynamics. In recent years,

computational modelling of organic materials has delved deep into organic electronics,

especially in the screening and design of potential candidate molecules for applications in

devices such as organic light emitting diodes (OLEDs), organic field effect transistors

2

(OFETs) and photovoltaic cells. Quantum computational methods help to identify potential

applications of molecular systems in OLED, NLO and sensing devices.

There is a current felt need to develop efficient lighting systems to replace the traditional

and inefficient ones which have large power losses. Inorganic LEDs, liquid crystal displays

(LCDs) and plasma displays are the leading technologies in the market today. However,

these devices are quite difficult to use in terms of cost, size, efficiency, low viewing angle

and colour tunability. A remarkable revolution has been observed with the introduction of

organic materials in the field of optoelectronics. In 1987, Tang and VanSlyke first reported

the highly efficient two-layer green OLED, which evoked great interest in developing

OLED based devices. Today, researchers are working on developing these OLED devices

with high resolution, brightness and contrast with improved colour variations.

NLO effect was first identified in 1875 during the discovery of Kerr effect. Until the

invention of the laser in 1960, the importance of NLO effect was not exploited adequately.

Later a better understanding of this phenomenon motivated researchers to develop devices

based on this effect. The past few years have seen many investigators research on the

optical power limiting behavior of a number of novel materials primarily for the protection

of the human eye and sensitive optical detectors from intense laser beams. The first optical

limiter was reported by Leite et al. in 1967 using the continuous wave laser beam. Although

it is common knowledge that optical limiters have the ability to attenuate intense laser

beams, recent years have seen research efforts intensify on the selection of proper materials

for optical limiting devices. Studies of optical limiting using the Z-scan technique have

resulted in the recognition that nanomaterials are good optical limiters.

There has been a longstanding scientific interest in organic compounds adsorbed on metal

nanoparticle (NP) surfaces as the adsorption of these compounds play vital roles in altering

3

their catalytic, sensing and opto-electrical properties. Among the metal (Ag, Au, Cu) NPs,

Ag NPs show the strongest surface plasmon resonance coupled with high conductivity and

so has been the subject of intense research. Subsequently, they find extensive application

in catalysis, biological labelling, photonics and optoelectronics as well as in metal ion

detection studies. Further, studies report that the behaviour of functionalized metal NPs

provide excellent photo and thermal stability as compared to their metal counterparts.

Nonlinear optical (NLO) and sensing properties of different nanomaterials have been under

investigation for the last few decades. Presently, studies have indicated that Ag NPs capped

with organic molecules are promising candidates for NLO and sensing applications.

One area of concern among the research community is in detecting heavy metal ions due

to its severe toxic impact on living systems in the environment. Of these metal ions,

mercury (Hg) is one of the most dangerous and is widely distributed in air, water and soil.

Due to its high water-soluble nature, mercuric ions (Hg2+) in water can lead to severe

impairment in the brain, nervous system and kidneys. Detection of mercury ions in the

environmental and biological samples, with high sensitivity and selectivity, is therefore of

paramount importance.

This research work focuses on three major optical applications namely OLED, optical

limiters and metal ion sensors. Density functional theory (DFT) computations reveal that

among acene systems, pyrene is the best nonlinear acene system for these optical

applications. Further the nonlinearity and sensing behaviour of pyrene adsorbed on silver

is analyzed using both theoretical and experimental techniques.

On the premise that the efficiency of pyrene can be drastically improved if its derivatives

were used, eleven of its derivatives are considered; the next step is to determine the best

derivative.

4

In order to select the best molecular system for OLED applications, charge transport

properties are carefully investigated for pyrene and its derivatives. Of these,

hydroxypyrene and aminopyrene, satisfy the requirements for hole transport and electron

transport layers respectively and are suggested as materials for OLED device fabrication.

Next, to find out the best molecule for NLO applications among the pyrene derivatives,

hyperpolarizability calculations are performed and nitropyrene is predicted to have high

hyperpolarizability. Further, its adsorption on Ag is analysed using both theoretical and

experimental techniques for NLO applications. Metal ion sensing ability of nitropyrene

capped Ag is also investigated which is comparatively higher than pyrene-Ag system.

Hence among the eleven derivatives, nitropyrene is selected for optical limiting and metal

ion sensor applications. A summary of the entire research work is represented

diagrammatically in Fig.1 & 2.

The report of the work done is organized into seven chapters. Chapter-I introduces the

area of study, elaborates on it through literature survey and states the motivation for the

selected research topic. Chapter-II discusses the theory behind the DFT and TDDFT

modelling and the rationale for choosing particular basis set and functionals under different

situations. Experimental techniques used in the research work are also discussed here.

5

Figure 1 Selecting small acenes and its derivatives for optoelectronic applications.

Figure 2 Investigations of molecular systems for Optoelectronic Applications.

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Chapter-III reports the DFT computations of small nonlinear acenes (n=3,4) for NLO and

OLED applications. Reorganization energy and singlet exciton generation fraction helps

in identifying a suitable molecule among small nonlinear acenes, for OLED application.

The computed hole reorganization energies are lower than the electron reorganization

energies suggesting that these systems can be used as hole transport layers in OLED

devices. Having large value of reorganization energies, the 3 ring nonlinear systems are

not suitable for efficient hole transportation. The higher singlet exciton generation fraction

of pyrene suggests that it could be used as a highly efficient emissive layer in OLEDs.

Adsorption of the nonlinear acenes on silver causes an enhancement in the first

hyperpolarizability. These computed values together with the Harmonic oscillator model

of aromaticity (HOMA) indexes of the molecular systems are analysed to determine their

NLO properties. The outcome suggests that pyrene-Ag would exhibit better NLO behavior

as compared to other nonlinear acenes.

The charge transfer mechanisms of nonlinear fused 4 ring systems adsorbed on silver is

analysed using the molecular electrostatic potential (MEP) plot, computed charges and

natural bond orbitals (NBO). The plot of MEP and its charges provides a reliable indication

of the charge transfer from the nonlinear fused 4-ring systems to the silver cluster. These

results are further analysed by NBO analysis, where additional orbital overlap between π

C–C bonds of the molecules with Ag atoms are identified as expected. The adsorption

process is further confirmed from the peaks simulated at lower frequencies in the Raman

spectrum confirming strong adsorption interactions between the molecular system and the

cluster. Enhancement in certain additional peaks in the Raman spectrum indicates the

orientation of these molecular systems on the Ag surface. This investigation paves the way

for application of pyrene in the field of OLED and NLO devices.

7

Chapter IV reports the adsorption process of pyrene on silver and its applications in NLO

and metal ion sensors which are investigated using both experimental and through

computational techniques. The adsorption process is confirmed by the presence of a red

shift in the simulated and experimental UV-Vis spectra and by additional vibrational

modes being excited in the Raman spectrum. The SERS results show vibrational modes

which match with the predictions of the simulated theoretical Raman spectrum. XRD

analysis gives the grain size while the field emission scanning electron microscope

(FESEM) confirms the presence of spherical-like nanoparticles.

The NLO behavior of the investigated system is identified by open aperture Z-scan

technique. As compared to pyrene, enhanced nonlinear absorption and optical limiting is

seen in Py-Ag NPs which point towards a possible use of pyrene adsorbed on silver in the

rational design of optical limiting devices. The mechanism behind the transfer of electronic

charge has been identified from the shifting of frontier molecular orbitals and further

confirmed by the Fukui calculations which predict the electrophilic nature of the silver

cluster in the presence of pyrene. Metal ion sensing behavior of Py-Ag NPs are investigated

using the calorimetric technique. Upon addition of Hg ions, Py moves away from the

surface of Ag, to form the Ag-Hg NPs due to the strong interaction between Ag NPs and

the mercury ions resulting in a total quenching of SPR peak which is further validated by

the theoretical approach.

Chapter-V deals with the theoretical investigations on charge transport properties of

pyrene and eleven of its mono substituted derivatives for potential use as effective

materials for OLED devices. Computations on the reorganization energies and energy level

alignment, help to identify the best pyrene derivatives for OLED applications.

Reorganization energy computations indicate that pyrene and its derivatives are more

suitable for hole transport except two derivatives - Aminopyrene and pyrene acetic acid –

8

which are identified as an electron transport material. It is predicted that hydroxypyrene

(PyOH) and aminopyrene (APy) would show better performance as a hole transport layer

(HTL) and an electron transport layer (ETL) material respectively among the pyrene

derivatives. The movement of charges from anode to PyOH and cathode to APy are

analysed using Fukui calculations. The hole and electron mobility of PyOH and APy are

calculated using Marcus theory.

Higher singlet exciton generation fraction reveals that PyOH and APy can be used as highly

efficient emissive layers in OLEDs. The absorption and emission spectra of both the

molecules are simulated to identify their use as an emissive layer in OLED devices. Higher

singlet exciton generation fractions together with the results obtained from energy level

alignment and mobility calculations suggests that PyOH and APy are potential candidates

for OLED devices.

In order to find an effective material for NLO applications, hyperpolarizability

computations of pyrene and eleven of its mono substituted derivatives are performed. Out

of the set of molecules, nitropyrene (NPy) is identified as an efficient molecule for NLO

applications.

Chapter VI reports the adsorption of NPy on silver through computational and

experimental techniques. Using DFT, variations in geometrical parameters are identified

in regions of NPy near the silver cluster. The UV-Vis spectra of the investigated system

are simulated theoretically and observed experimentally. Theoretical and experimental

SERS studies reveal the adsorption of the molecule through the -NO2 moiety of NPy in a

perpendicular orientation on Ag surface. Using XRD technique, the average crystallite size

of the NPy-Ag NPs is determined and the shape of the NPy-Ag NPs is identified as

nanorods from FESEM analysis.

9

Charge transfer mechanisms due to the interaction between NPy and silver are analysed

with the help of the plot of MEP and its charges, Fukui calculations and the orbital overlap

from NBO analysis. Results confirm the charge transfer from silver to NPy. NLO

calculations reveal that NPy-Ag3 has a larger hyperpolarizability value as compared to that

of urea which is the standard NLO material. Additionally, the Z-scan studies predict the

enhanced optical limiting behavior of NPy-Ag NPs, confirming that it is well suited in the

design and development of NLO materials. Using colorimetric detection, it is found that

the NPy-Ag NPs have the ability to identify the mercury ions by a total quenching of SPR

peak, which confirms the sensing ability of the NPy-Ag system. The study indicates that

NPy-Ag NPs is a promising candidate for NLO and sensor devices.

A final section of the thesis gives the summary, conclusions and future directions that the

research can be take.

Papers published/Communicated to Journals

Included in the Thesis

Electron transport and optical properties of pyrene derivatives for OLED

Applications. U.Reeta Felscia, Beulah J.M.Rajkumar and M.Briget Mary, Organic

Electronics (Communicated)

Theoretical and experimental investigations of nitropyrene on silver for nonlinear

optical and metal ion sensing applications. U.Reeta Felscia, Beulah J.M.

Rajkumar, Pranitha Sankar, Reji Philip and M.Briget Mary, Materials Chemistry

and Physics 243(2020)12466. (IF-3.408)

Charge transport properties of pyrene and its derivatives: optoelectronic and

nonlinear optical applications. U. Reeta Felscia, Beulah J. M. Rajkumar and M.

Briget Mary, Journal of Material Science, 53 (2018)15213-15225 (IF-3.553)

10

Theoretical investigations on nonlinear fused 4-ring systems: Application to OLED

and NLO devices. U. Reeta Felscia, Beulah J.M. Rajkumar and M. Briget Mary,

Synthetic Metals 246 (2018) 31–38. (IF-3.286)

Optical nonlinearity and charge transfer analysis of pyrene adsorbed on silver:

Computational and experimental investigations. U. Reeta Felscia, Beulah J.M.

Rajkumar, Pranitha Sankar, Reji Philip and M. Briget Mary, Spectrochimica Acta

Part A: Molecular and Biomolecular Spectroscopy 184 (2017) 286-293. (IF-3.232)

Not related to the present reported research work

Electronic and Nonlinear optical properties of L-Histidine adsorbed on silver: A

Theoretical and Experimental approach. U. Reeta Felscia, Beulah J.M. Rajkumar,

Monickaraj Nidya and Pranitha Sankar. Journal of Physical Chemistry A. 122

(2018) 1045-1052. (IF-2.641)

Computational study of quinacridone on silver and gold clusters: Applications to

organic light emitting diodes and nonlinear optical devices. U. Reeta Felscia and

Beulah J.M. Rajkumar. Materials Letters 221 (2018) 318–321. (IF-3.204)

Papers presented/Participated in Conferences & Symposiums

Presented a Paper entitled Computational Study of Aminonitropyrene on Silver:

Applications to Nonlinear Optical Devices in the ‘International Conference on

Recent Trends in Mathematical & Physical Modelling and Bioresource

Management Strategies’ organized by Thiagarajar College, Madurai on February

12th & 13th ,2019.

Presented a Poster entitled Computational Investigations of quinacridone on

silver and gold clusters: Application to Nonlinear Optical and OLED devices

in the ‘International Conference on Spectroscopy of biomolecules and advanced

11

materials’ organized by Christian College, Chengannur, Kerala on October 4th

&7th, 2017.

Presented a Paper entitled Electronic, optical and vibrational analysis of

nitrobenzene adsorbed on silver cluster in the ‘National conference on current

advancement in Physics’ Organized by St.John’s College, Palayamkottai on

February 3rd & 4th,2017. ISSN:2278-4861.

Presented a Paper entitled Computational Investigations on the optical and

vibrational analysis of aniline adsorbed on silver cluster in the ‘International

Conference on Recent Trends in Materials Science and Applications’ organized by

Sri Meenakshi Government Arts college for Women on January 6th, 2017.

Presented a Poster entitled Electronic and Optical Properties of Phenanthrene

adsorbed on silver cluster-A theoretical study in the ‘National Conference on

Advanced Materials-2016’ organized by St.Joseph’s College on October 7th, 2016.

Presented a Paper entitled Electronic and Optical Properties of Pyrenemethanol

Adsorbed on Silver: A Theoretical Approach in the ‘International Seminar on

Nanoscience and Technology’ Organized by Mother Teresa Women’s University

on September 20th, 2016.

Presented a Paper entitled Electronic and Optical Properties of Pyrenebutanol

adsorbed on Silver: A Theoretical Approach in the ‘National Conference on

Smart Materials’ organized by Lady Doak College during February 23rd &

24th,2016. ISBN 978-81-900971-9-2.

Presented a Poster entitled Theoretical Investigation on the NLO and Charge

Transfer Properties of Diphenylamine Adsorbed on Silver Cluster in the

‘International Conference on Recent Advances in Materials and Chemical

12

Sciences’ organized by Gandhigram Rural Institute during December 14th & 15th,

2015. ISBN 978-93-85477-46-1

Presented a Poster entitled Investigation on the NLO Property of Beta Carotene

Adsorbed on Silver in the ‘International Conference on Nanomaterials for

Energy, Environment, Catalysis and Sensors’ organized by Madurai Kamaraj

University during December 11th & 12th, 2015.

Participated in a ‘Workshop on the Applications of Computational Chemistry’,

Organized by the Royal Society of Chemistry at Madurai Kamaraj University on

October 12th, 2015.

Presented a Poster entitled Theoretical investigation of structure, electronic and

non-linear optical properties of Quinacridone in the ‘National Conference on

Advanced Functional Materials and Applications’ organized by Kalasalingam

University during April 2nd &3rd,2015.