Design and Engineering of Organic Molecules for Customizable

Terahertz Tags

Shaumik Raya, Jyotirmayee Dash

a,c, Kathirvel Nallappan

a, Vaibhav Kaware

b, Nitin Basutkar

b,

Ashootosh Ambadeb, Kavita Joshi

b, Bala Pesala

a,c

aCSIR- Central Electronics Engineering Research Institute, CSIR Madras Complex, Chennai, India

bCSIR- National Chemical Laboratory, Pune, India

cAcademy of Scientific and Innovative Research, CSIR-SERC, Chennai, India

Email: balapesala@gmail.com

ABSTRACT

Terahertz (THz) frequency band lies between the microwave and infrared region of the electromagnetic spectrum.

Molecules having strong resonances in this frequency range are ideal for realizing "Terahertz tags" which can be easily

incorporated into various materials. THz spectroscopy of molecules, especially at frequencies below 10 THz, provides

valuable information on the low frequency vibrational modes, viz. intermolecular vibrational modes, hydrogen bond

stretching, torsional vibrations in several chemical and biological compounds. So far there have been very few attempts

to engineer molecules which can demonstrate customizable resonances in the THz frequency region. In this paper,

Diamidopyridine (DAP) based molecules are used as a model system to demonstrate engineering of THz resonances (<

10 THz) by fine-tuning the molecular mass and bond strengths. Density Functional Theory (DFT) simulations have been

carried out to explain the origin of THz resonances and factors contributing to the shift in resonances due to the addition

of various functional groups. The design approach presented here can be easily extended to engineer various organic

molecules suitable for THz tags application.

Keywords: Terahertz Spectroscopy, Density Functional Theory (DFT), Diamidopyridine (DAP)

1. INTRODUCTION

Terahertz (THz) radiation is a part of electromagnetic spectrum ranging from 0.1 to 10 THz (with wavelengths from 3

mm to 30 µm). Until recently, this particular frequency region hasn’t been widely explored for commercial applications

due to the unavailability of suitable low cost and high power sources [1]. As a result, THz portion of the electromagnetic

spectrum was referred to as THz gap. Recent developments in continuous wave and time-domain THz systems in

providing wide frequency range THz sources has made THz technology a potential tool for various applications in

medicine, microelectronics, agriculture and security [2].

In order to design THz tags, it is important to understand the vibrational modes contributing to resonances in the THz

frequency range. Studies on THz vibrational modes of various organic molecules have been done to understand the

reason behind these resonances, which are mainly due to intermolecular and intramolecular vibrations, hydrogen bond

stretching and torsional vibrations [3,4]. Of particular interest are the molecules containing hydrogen bonds. Since

hydrogen bond is a weak bond, resonances due to the hydrogen bond stretches occur at lower THz frequencies (< 2

THz), which is of significant interest in the present study towards designing molecules with resonances in lower THz

frequency range. Earlier studies on ATGC, main components of DNA, show that the low frequency vibrational modes

(<4 THz) are dominated by intermolecular hydrogen bond bending [5]. The origin of these resonances is understood by

carrying out density functional theory (DFT) simulations. Ge et al. [6] reported the spectroscopy results of 4-

Hydroxycinnamic acid derivatives in a frequency region between 0.3-2 THz and assigned the individual THz spectra as

scissoring/twisting or stretching of the dimer linked by hydrogen bonds. Biotin and lactose were studied because of the

presence of narrow resonances below 1 THz. Allis et al. have explained the reason behind the lowest THz absorption

signatures in Biotin and Lactose Monohydrate [7]. The narrow THz line shapes of these molecules are due to the

decoupling of single vibrational modes from nearby modes and due to intermolecular interaction in molecular crystals.

DFT simulations of Lactose show that the resonances below 1 THz are mainly due to the rotational motions (0.525 THz)

and intramolecular twisting motions (0.86 THz). Recently, THz spectroscopy has been used to study the hydration

dynamics in various biomolecules [8, 9]. Low frequency vibrations in biomolecules occur in the picosecond time scale

which resonates at THz frequencies. Low frequency modes, especially those found in proteins are linked to large

Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications VII,edited by Laurence P. Sadwick, Créidhe M. O'Sullivan, Proc. of SPIE Vol. 8985, 89850P

2014 SPIE · CCC code: 0277-786X/14/$18 · doi: 10.1117/12.2041194

Proc. of SPIE Vol. 8985 89850P-1

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms

vibrations of the molecule. Hydration studies are important to understand the role of water in various bio-chemical and

signaling processes occurring at the cellular level. Based on these studies, it can be inferred that THz resonances are

mainly due to the intermolecular vibrations (in-plane/out-of-plane bending modes).

So far, there have been few studies towards designing and engineering of molecules in the THz region. Molecules with

strong resonances at lower THz frequencies, especially at frequencies < 1 THz, are ideal for realizing THz tags since

very few molecules have resonances in this region. Moreover, these molecular THz tags can be easily incorporated into

various materials/substrates, enabling effective detection of counterfeits in security and pharmaceutical industries [10].

Based on spring-mass methodology, resonances can be fine-tuned either by changing the molecular mass or by changing

the force constant of the intramolecular/intermolecular bonds. Using this principle, we present significant results towards

the design and engineering of various Diamidopyridine (DAP) based molecules which show customizable resonances in

the THz region (< 10 THz). DFT simulations have been carried out to understand the origin of these THz resonances and

factors contributing to the shift in resonances due to the addition of various functional groups [5-7]. The design approach

presented here can be readily extended to design various molecular THz tags.

2. DESIGN OF DIAMIDOPYRIDINE (DAP) BASED MOLECULES

THz resonances can be customized and fine-tuned by including various functional groups, which result in different

molecular mass and/or intramolecular/intermolecular bond strengths. The customization of THz resonances can be linked

to spring-mass analogy. Molecular bonds vibrate in a manner that is similar to a spring-mass system undergoing simple

harmonic motion. Each molecular vibration will have different resonance frequency, which mainly depends on the bond

strength (the spring constant in a spring-mass system) and the reduced mass of the molecule. Using a simple harmonic

oscillator model of a diatomic molecule (A-B), the vibrational frequencies can be calculated as:

1

2

kf

(1)

Where 'k' is the force constant in the atomic scale and the spring constant for macroscopic model respectively, and μ is

the reduced mass given by

.A B

A B

m m

m m

(2)

Where mA and mB are the mass of the atoms in the molecule A-B. The strength of the chemical bond in the molecule A-

B is mainly characterized by the force constant [11]. Therefore, weaker the chemical bond (electronic effect) and larger

the reduced mass μ (mass effect), the lower is the resonance frequency [11]. It implies that, resonance frequencies of in-

plane stretching vibrations in general are higher than those of bending vibrations because the rhythmical movement

along the bond axis is associated with larger force constant compared to the change in the bond angle. Using a similar

analogy, out-of-plane bending vibrations or torsions have lower frequencies than in-plane bending vibrations. By adding

functional groups, the bond strength and the reduced mass can be changed, hence the resonance frequencies in the THz

range (< 5 THz) can be effectively tuned.

Mono-PhDAP N-(6-amidopyridin-2-

yl) benzamide

Pr-PhDAP N-(6-propion

amidopyridin-2-yl)

benzamide

PhDAP (N,N’-(pyridine-2, 6-

diyl) dibenzamide)

4-NO2-PhPhDAP N-(6-benzamido pyridin-2-

yl)-4-nitrobenzamide

Chart 1: Structure of PhDAP and its derivatives

Based on this methodology, THz molecules have been designed having higher molecular mass (mass effect) and tunable

intramolecular/intermolecular bond strengths (electronic effect). In the present study, higher molecular mass has been

realized by considering molecules with multiple aromatic rings and lower force constant has been achieved by adding

various functional groups. Electronegative atoms such as Nitrogen are incorporated in the aromatic structures (called

heterocyclic structures) instead of only benzene rings in order to vary the bond strength easily. Functional groups

containing Nitrogen are integrated on minimum of two positions of the heterocyclic ring to realize multiple

Proc. of SPIE Vol. 8985 89850P-2

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms

intramolecular/intermolecular hydrogen bonds. Molecules either with two aromatic rings (Mono-PhDAP) and its

derivative (Pr-PhDAP) or with three aromatic rings (PhDAP) and its derivative (4-NO2Ph-PhDAP) have been

synthesized using this design. Chart 1 shows the molecular structure of these molecules.

3. THZ SPECTROSCOPY OF DIAMIDOPYRIDINE BASED DERIVATIVES

The primary focus of the study is to investigate the effect of changing molecular mass and the force constant on the THz

resonances. Mono-PhDAP has been chosen as the base molecule and hydrogen atom of –NH2 group has been replaced

with CO-CH2-CH3 in Pr-PhDAP to observe the change in resonance due to its addition. Similarly, one more aromatic

ring has been added to Mono-PhDAP to change the molecular mass significantly. Further, hydrogen atom at 4th

position

in PhDAP is replaced with –NO2 to observe the change in resonance due to change in the bond strength and reduced

mass. These four molecules have been designed and synthesized using the following general procedure.

3.1 Synthesis of PhDAP

In a round bottom flask, 2,6‐diamidopyridine (1g, 9.163 mmol) was dissolved in 40mL of dry dichloromethane and

triethylamine (2.8mL, 27.72mmol) was added. Then, benzoyl chloride (2.5 mL, 17.98 mmol) was added drop by drop

and this mixture was stirred under inert atmosphere at room temperature for 15h. Reaction mixture was poured in water.

Crude product was extracted in dichloromethane, organic layer was washed with water and dried over anhydrous sodium

sulphate. The solvent was evaporated on rotary evaporator and crude product was purified by column chromatography

on silica gel by eluting with ethyl acetate: hexane (40:60) mixture. The product was further purified by recrystallization

using methanol. Similarly, other molecules have also been synthesized with high purity.

3.2 Sample Preparation

Powdered samples suitable for THz spectroscopy were prepared by mixing with high density polyethylene (HDPE) in

the ratio of roughly 30:70 by concentration. Smooth pellets with a thickness of 1 mm were prepared after applying a

pressure of 15 tonnes in a Potassium Bromide (KBR) press unit for 2 minutes. The samples have been scanned in a

Nicolet 6700, Thermo-Scientific instrument capable of taking THz measurements over a wide frequency range (2 THz to

21 THz). The spectrum obtained is averaged for 36 times with a spectral resolution of 4 cm-1

.

3.3 Terahertz Spectroscopy results

Figure 1(a) shows comparison of experimental spectra of Mono-PhDAP and Pr-PhDAP and fig. 1(b) shows the

comparison of experimental spectra of PhDAP and 4-NO2Ph-PhDAP. Experiments have been carried out with two

pellets of each chemical in order to verify the repeatability of the results. The experimental results show significant

differences in the THz resonances both in the shape of the spectrum and in the position of the peaks due to the change in

chemical structure of the molecules. This change in resonances can be attributed to the change in the molecular masses

and strength of intermolecular/intramolecular bonds.

Fig.1(a): Comparison of experimental THz spectra of Mono-

PhDAP and Pr-PhDAP

Fig. 1(b): Comparison of experimental THz spectra of PhDAP

and 4-NO2Ph-PhDAP

2 3 4 5 6 7 8 9 100.2

0.4

0.6

0.8

1

Frequency(THz)

Ab

so

rba

nc

e (

a.u

)

Pr-PhDAP

Mono-PhDAP

**

*

*

2 3 4 5 6 7 8 9 100.2

0.4

0.6

0.8

1

Frequency(THz)

Ab

so

rba

nc

e (

a.u

)

PhDAP

4NO2-Ph-PhDAP

*

*

*

***

Proc. of SPIE Vol. 8985 89850P-3

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms

From fig. 1(a) it is seen that, resonances are changed by replacing hydrogen in –NH2 with CO-CH2-CH3, in Mono-

PhDAP structure. Similarly, fig. 1(b) shows the shift in resonances due to addition of –NO2 to PhDAP structure. The

resonances having the same mode of vibration, as discussed in the simulation results below, have been compared and are

marked in the figure. Interestingly, some of the resonances are shifted to lower frequencies while some are shifted to

higher frequencies. Here, we attempt to explain this behaviour by quantifying the relative contribution of two important

factors: mass effect and force constant effect. To understand the contribution of each of these effects, DFT simulations

using Gaussian 09 package [12] have been carried out.

4. DFT SIMULATION RESULTS

Over the years, DFT calculations have become an effective tool to predict molecular structures, charge transfer

interactions as well as intermolecular and intramolecular vibrations. DFT calculations are carried out using hybrid

functional Becke-3-Lee-Yang-Parr (B3LYP) method. The valence double-zeta polarized basis set with six d-type

Cartesian-Gaussian polarization functions (6-31G (d)) was found to give converged results [3]. Here, DFT simulations

have been carried out by considering single molecule and the results are compared with experiments. The results agree

well at higher frequencies (> 5 THz). In future, DFT simulations will be extended to simulate the molecules including

their full crystal structure for accurate prediction of resonances especially at lower THz frequencies.

5. ANALYSIS OF THZ RESONANCES

5.1 Comparison of Mono-PhDAP and Pr-PhDAP

Comparison of experimental and simulated spectra of Mono-PhDAP and Pr-PhDAP are shown in fig. 2(a) and 2(b)

respectively.

Fig. 2(a): Comparison of experiments and DFT simulation

results of Mono-PhDAP

Fig. 2(b): Comparison of experiments and DFT

simulation results of Pr-PhDAP

From the figures, it can be seen that the simulation results match relatively well at higher frequencies (> 5 THz)

compared to lower THz frequencies. This is expected since prediction of resonances at low frequencies resulting from

intermolecular vibrations would need full crystal simulations.

Table1: Comparison of experimental and simulated resonances of Mono-PhDAP and Pr-PhDAP

2 4 6 8 100

0.2

0.4

0.6

0.8

1

Frequency (THz)

Ab

so

rban

ce (

a.u

)

Experiments

Simulations

2 4 6 8 100

0.2

0.4

0.6

0.8

1

Frequency (THz)

Ab

so

rban

ce(a

.u)

Experiments

Simulations

Mono-PhDAP Pr-PhDAP

Experimental

resonances (THz)

Simulated

resonances (THz)

Experimental

resonances (THz)

Simulated

resonances (THz)

2.72 2.71 2.6 2.61

5.09 4.98 3.64 3.59

6.36 6.56 4.80 5.05

8.51 8.26 7.06 6.37

9.95 9.72 8.45 8.67

9.37 9.36

Proc. of SPIE Vol. 8985 89850P-4

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms

For the purpose of understanding the origin of THz resonances, we have only considered resonances which are in

reasonable agreement with the DFT simulations. These are 2.72 (2.71 THz), 5.09 (4.98 THz), 6.36 (6.56 THz), 8.51

(8.26 THz) and 9.95 (9.72 THz) in case of Mono-PhDAP. Similarly for Pr-PhDAP, the closely matching frequencies are

2.6 (2.61 THz), 3.64 (3.59 THz), 4.80 (5.05 THz), 7.06 (6.37 THz), 8.45 (8.67 THz) and 9.37 (9.36 THz). Table 1 shows

the comparison of experiments and DFT simulation results of Mono-PhDAP and Pr-PhDAP.

Figure 3 shows how the resonance frequency having same mode of vibration is changed by replacing hydrogen in –NH2

with -CO-CH2-CH3 in Mono-PhDAP structure. It is observed that Pr-PhDAP has lower resonance frequency compared to

Mono-PhDAP around 2 THz. Comparisons between the molecules have been done at lower frequencies since the

eventual goal of this study is to design organic molecules with resonances below 1 THz (even though experimental

results below 2 THz are unavailable at present as it is beyond the capability of our instrument). To understand the reason

behind shift in frequencies, the exact mode of vibration has been examined, which is shown in fig. 3(a) and 3(b).

Fig. 3(a): Mode of vibration of monoPhDAP at

2.09 THz (69.66 cm-1)

Fig. 3(b): Mode of vibration of PrPhDAP at

1.81 THz (60.49 cm-1)

This is primarily an out-of-plane bending vibration of the two Pyridine rings about the N-C bond. In addition, there is

also twisting of oxygen and nitrogen atom across carbon atom. Pr-PhDAP has a lower resonance mainly due to the

decrease in force constant from 0.017 to 0.012 N/m as given in table 2. Interestingly, inspite of increase in the molecular

mass, reduced mass of Pr-PhDAP is less than that of Mono-PhDAP in this mode of vibration. Further studies are needed

to understand the reasons behind the reduction in the reduced mass. We have also compared other resonances (below 10

THz) to understand the origin of the differences in resonance frequencies in table 2.

Table 2: Comparison of resonances of monoPhDAP and Pr-PhDAP and the mode of vibration at these frequencies

Mono-PhDAP

PrPhDAP

Force

constant (k)

(N/m)

Reduced

mass (μ)

(amu)

Resonant

frequency

(THz)

Force

constant (k)

(N/m)

Reduced

mass (μ)

(amu)

Resonant

frequency

(THz)

Reason behind the

resonances

0.017 5.93 2.09 0.012 5.55 1.81

Out of plane bending of

the molecule with slight

twisting of N and O

across C

0.078 4.83 4.98 0.082 4.93 5.05

Out of plane bending of

both the rings due to C=O

oscillations

0.342 5.51 9.72 0.362 6.32 9.36

In-plane bending of both

the rings due to C=O

oscillations

The second compared frequency which is near 5 THz in case of Pr-PhDAP is due to higher force constant of Pr-PhDAP

compared to Mono-PhDAP. The reduction in resonance of Pr-PhDAP (9.36 THz) compared to Mono-PhDAP (9.72 THz)

is mainly due to the increase in the reduced mass. In summary, from the simulation results, shift in the resonances to

Proc. of SPIE Vol. 8985 89850P-5

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms

higher or lower frequencies upon adding a functional group can be clearly explained as a spring constant effect or

reduced mass effect. Detailed experimental studies are planned in order to better understand the mass/spring constant

effects by replacing/adding a single atom in the same molecular structure.

5.2 Comparison of PhDAP and 4-NO2Ph-PhDAP

In order to increase the reduced mass, structure with three aromatic rings (PhDAP) and its derivative 4-NO2Ph-PhDAP

have been synthesized and characterized using THz spectroscopy. Comparison between PhDAP and its derivative 4-

NO2Ph-PhDAP shows how the resonances are changing by adding the electron-withdrawing functional group (–NO2) to

PhDAP molecule. Figures 4(a) and 4(b) show the experimental and simulated spectra of PhDAP and 4-NO2Ph-PhDAP

respectively.

Fig. 4(a): Comparison of THz experiments and DFT

simulation spectra of PhDAP.

Fig. 4(b): Comparison of THz experiments and DFT

simulation spectra of 4-NO2Ph-PhDAP

Similar to the analysis in the case of Mono-PhDAP compounds, we have considered the frequencies which are matching

closely with simulation results. The matched frequencies in PhDAP are 2.6 (2.86 THz), 5.15 (5.24 THz), 5.61 (5.57

THz), 7.35 (7.24 THz), 8.16 (8.36 THz), 8.79 (9.05 THz). Similarly, for 4-NO2Ph-PhDAP, the matched frequencies are

2.95 (3 THz), 4.51 (4.72 THz), 4.8 (5.08 THz), 5.55 (5.22 THz), 6.94 (6.78 THz), 8.39 (8.57 THz) and 9.08 (8.97 THz)

which is given in table 3.

Table3: Comparison of experimental and simulated resonances of PhDAP and 4-NO2Ph-PhDAP

By comparing the lowest mode of vibration of mono-PhDAP and PhDAP, we can see that PhDAP (1.89 THz) has lower

resonance as compared to Mono-PhDAP (2.09 THz). This is clearly due to the increase in reduced mass since the force

constant of both molecules are same (as seen in table 2 and 4). From the simulations, we also observe that 4-NO2Ph-

PhDAP has lower resonance frequency compared to PhDAP at around 1.8 THz. To understand the origin of this

resonance, the exact mode of vibration has been investigated, which is shown in fig. 5(a) and 5(b).

2 3 4 5 6 7 8 9 100

0.2

0.4

0.6

0.8

1

Frequency (THz)

Ab

so

rba

nc

e(a

.u)

Simulations

Experiments

2 3 4 5 6 7 8 9 100

0.2

0.4

0.6

0.8

1

Frequency (THz)A

bs

orb

an

ce

(a

.u)

Experiments

Simulations

PhDAP 4-NO2Ph-PhDAP

Experimental

resonances (THz)

Simulated

resonances (THz)

Experimental

resonances (THz)

Simulated

resonances (THz)

2.6 2.86 2.95 3

5.15 5.24 4.51 4.72

5.61 5.57 4.8 5.08

7.35 7.24 5.55 5.22

8.16 8.36 6.94 6.78

8.79 9.05 8.39 8.57

9.08 8.97

Proc. of SPIE Vol. 8985 89850P-6

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms

Fig. 5(a): Mode of vibration of PhDAP at

1.89 THz (63.11cm-1)

Fig. 5(b): Mode of vibration of 4-NO2Ph-PhDAP at

1.73 THz (57.72 cm-1)

The mode of vibration shown in fig. 5(a) and 5(b) is primarily an out of plane bending of the molecule due to twisting of

Oxygen and Nitrogen across the Carbon atom. The resonance frequency of 4-NO2Ph-PhDAP is less as compared to

PhDAP due to lower force constant which is given in table 4. We have also compared other resonances (below 10 THz)

to understand the origin of the differences in resonance frequencies between these molecules.

Table 4: Comparison of resonances of PhDAP and 4-NO2-Ph-PhDAP and the mode of vibration at these frequencies

PhDAP

4-NO2-Ph-PhDAP

Force

constant (k)

(N/m)

Reduced

mass (μ)

(amu)

Resonant

frequency

(THz)

Force

constant (k)

(N/m)

Reduced

mass (μ)

(amu)

Resonant

frequency

(THz)

Reason behind the resonances

0.017 7.38 1.89 0.014 7.07 1.73

Out of plane bending of the

molecule due to twisting of O

and N across C

0.115 5.68 5.57 0.098 5.49 5.22

Out of plane bending of the

middle and one side ring and in-

plane bending of the other

aromatic ring

0.196 5.71 7.24 0.191 6.33 6.78 In-plane bending of each of the

aromatic rings

0.367 6.84 9.05 0.371 7.04 8.97

In-plane bending of the

peripheral rings and out of plane

bending of middle ring

From table 4, the resonance frequency of 4-NO2Ph-PhDAP (around 5 THz) is less than that of PhDAP, which is mainly

due to the reduction in the force constant whereas lowering of the third resonance frequency (7 THz) is mainly due to the

increase in reduced mass. PhDAP has higher resonance around 9 THz mainly due to lower reduced mass of PhDAP than

4-NO2Ph-PhDAP. The resonances (with same vibrational mode) are shifted to lower frequencies due to the addition of

electronegative group (-NO2) to the PhDAP structure and is validated by the change in spring constant to reduced mass

ratio.

Binary molecular complexes with intermolecular hydrogen bonds have also been synthesized based on PhDAP

derivatives. The primary aim of this study is to realize resonances much lower than the resonances achieved with single

molecule. Preliminary results show that the Terahertz resonances can be further fine-tuned using this approach as the two

molecules in a binary complex are connected with intermolecular hydrogen bonds. Comparison of the resonances of the

complexes and individual molecules shows similar trends in the change of Terahertz resonances.

Proc. of SPIE Vol. 8985 89850P-7

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms

6. CONCLUSION

THz resonance frequencies of PhDAP based derivatives have been successfully customized by tuning the bond strengths

and by varying the molecular mass. We have been able to show both experimentally as well as with simulations, how the

THz resonances can be varied by adding more electronegative functional groups which is evident in the case of PhDAP

and 4-NO2Ph-PhDAP. Further, we have qualitatively explained the relative contribution of two important factors: mass

effect and force constant effect. To understand contribution of each of these effects, Density Functional Theory (DFT)

simulations have been carried out. This approach can be easily extended towards designing THz molecules, which can

show sharp prominent resonances below 1 THz suitable for realizing THz tags.

ACKNOWLEDGEMENTS

The authors like to thank Director General, CSIR and Director, CSIR-CEERI for their invaluable support throughout the

research work. Part of the research work has been carried out with equipment of CSIR innovation Complex for which

authors would like to thank Director, CSIR-SERC. Authors would also like to thank SIC, CEERI Chennai for his kind

support. Authors would like to acknowledge the financial support for this work through CSIR under network project

CSC-0128 (FUTURE).

REFERENCES

[1] Zomega Terahertz Corporation, “The Terahertz Wave eBook,” June 2012.

[2] X.-C. Zhang,JingzhouXu.,[Introduction to THz Wave Photonics],Springer 2010.

[3] M. Amalanathan, I. Hubert Joe, and S. S. Prabhu., "Charge Transfer Interaction and Terahertz studies of a

Nonlinear Optical Material L-Glutamine Picrate: A DFT study," J.Phys.Chem.A (2010).

[4] Keith C.Oppenheim,Timothy M. Korter,Joseph S. Melinger, and Daniel Grishkowsky,"Solid-state Density

Functional Theory Investigation of the Terahertz Spectra of the Structural Isomers 1,2-Dicyanobenzene and 1,3-

Dicyanobenzene,"J. Phys. Chem.A,114,12513-12521 (2010).

[5] B M Fisher,M Walther and P Uhd Jepsen,"Far-infrared vibrational modes of DNA components studied by

terahertz time-domain spectroscopy,"Institute Of Physic,S,Phys. Med. Biol. 47, 3807-3814 (2002).

[6] Min Ge, Hongwei Zhao, Wenfeng Wang, Zengyan Zhang, Xiaohan Yu, Wenxin Li, "Terahertz Time-Domain

Spectroscopy of Four Hydroxycinnamic Acid Derivatives," J Biol Phys 32:403–412 (2006).

[7] D.G. Allis, A.M. Fedor, T.M. Korter, J.E. Bjarnason, E.R. Brown,"Assignment of the lowest-lying THz

absorption signatures in biotin and lactose monohydrate by solid-state density functional theory," Chemical

Physics Letters 440, 203-209 (2007).

[8] Tatiana Globus, Aaron M. Moyer, Boris Gelmont, Tatyana Khromova, Maryna I. Lvovska, Igor Sizov and

Jerome Ferrance, "Highly Resolved Sub-Terahertz Vibrational Spectroscopy of Biological Macromolecules and

cells," IEEE Sensors Journal, Vol. 13, No. 1 (2013).

[9] D.Crompton, A.J.Vickers, "THz Spectroscopic Studies of Biomolecules," 2012 13th Biennial Baltic Electronics

Conference, Tallinn, Estonia (2012).

[10] Matthew D. King, Patrick M. Hakey, and Timothy M. Korter, "Discrimination of Chiral Solids: A Terahertz

Spectroscopic Investigation of L- and DL-Serine,"J. Phys. Chem, 114, 2945–2953 (2010).

[11] M.Reichenbacher and J.Popp, "Challenges in Molecular structure Determination," DOI 10.1007/978-3-642-

24390-5_2, Springer-Verlag Berlin Heidelberg (2012).

[12] Frisch M.J. et.al. Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford CT (2009).

Proc. of SPIE Vol. 8985 89850P-8

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/18/2014 Terms of Use: http://spiedl.org/terms