02057nas a2200217 4500008004100000245008000041210006900121260011700190300003200307490000900339520122200348100001701570700002201587700002501609700002001634700002001654700002201674700001801696700001701714856010801731 2014 eng d00aDesign and engineering of organic molecules for customizable terahertz tags0 aDesign and engineering of organic molecules for customizable ter aSan Francisco, CAbSPIE-Int Soc Optical Engineering, 1000 20th ST, PO Box 10, Bellingham, WA 98227-0010 USAcFEB aArticle Number: UNSP 89850P0 v89853 a

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.

1 aRay, Shaumik1 aDash, Jyotirmayee1 aNallappan, Kathirvel1 aKaware, Vaibhav1 aBasutkar, Nitin1 aAmbade, Ashootosh1 aJoshi, Kavita1 aPesala, Bala uhttps://library.ncl.res.in/content/design-and-engineering-organic-molecules-customizable-terahertz-tags02331nas a2200253 4500008004100000022001300041245010500054210006900159260000800228300001400236490000700250520146200257653002401719653003001743653001901773653002701792100002201819700001701841700001801858700002001876700002401896700002601920856013101946 2018 eng d a1866689200aTuning of terahertz resonances of pyridyl benzamide derivatives by electronegative atom substitution0 aTuning of terahertz resonances of pyridyl benzamide derivatives  cJUL a636–6500 v393 a

N-(pyridin-2-yl) benzamide (Ph2AP)-based organic molecules with prominent terahertz (THz) signatures (less than 5 THz) have been synthesized. The THz resonances are tuned by substituting the most electronegative atom, fluorine, at ortho (2F-Ph2AP), meta (3F-Ph2AP), and para (4F-Ph2AP) positions in a Ph2AP molecule. Substitution of fluorine helps in varying the charge distribution of the atoms forming hydrogen bond and hence strength of the hydrogen bond is varied which helps in tuning the THz resonances. The tuning of lower THz resonances of 2F-Ph2AP, 3F-Ph2AP, and 4F-Ph2AP has been explained in terms of compliance constant (relaxed force constant). Four-molecule cluster simulations have been carried out using Gaussian09 software to calculate the compliance constant of the hydrogen bonds. Crystal structure simulations of the above molecules using CRYSTAL14 software have been carried out to understand the origin of THz resonances. It has been observed that THz resonances are shifted to higher frequencies with stronger hydrogen bonds. The study shows that 3F-Ph2AP and 4F-Ph2AP have higher hydrogen bond strength and hence the THz resonances originating due to stretching of intermolecular hydrogen bonds have been shifted to higher frequencies compared to 2F-Ph2AP. The methodology presented here will help in designing novel organic molecules by substituting various electronegative atoms in order to achieve prominent THz resonances.

10aCompliance constant10aDensity functional theory10aPh2AP molecule10aTerahertz spectroscopy1 aDash, Jyotirmayee1 aRay, Shaumik1 aDevi, Nirmala1 aBasutkar, Nitin1 aGonnade, Rajesh, G.1 aAmbade, Ashootosh, V. uhttps://library.ncl.res.in/content/tuning-terahertz-resonances-pyridyl-benzamide-derivatives-electronegative-atom-substitution02413nas a2200253 4500008004100000022001400041245008700055210006900142260000800211300001200219490000900231520156800240653002401808653003401832653003001866653002701896100002201923700001701945700001801962700002001980700002602000700001702026856011602043 2019 eng d a0022-286000aFine-tuning of Terahertz resonances in hydrogen-bonded organic molecular complexes0 aFinetuning of Terahertz resonances in hydrogenbonded organic mol cMAY a495-5020 v11843 a

Novel organic molecular complexes have been designed and synthesized to obtain prominent Terahertz (THz) resonances in the low-frequency region. Intermolecular hydrogen bonds give rise to low-frequency THz resonances and hence binary organic molecular complexes of pyridyl alkylamide/benzamide (DAP) and hexyl thymine (C6THY) with multiple strong intermolecular hydrogen bonds (N-H–-O and N-H–-N) are designed and synthesized. THz resonances of the complexes are fine-tuned by varying the number of benzene rings in the DAP moiety (PrDAP + C6THY, PrPhDAP + C6THY and PhDAP + C6THY). DFT simulation studies of two molecule clusters have been carried out to understand the origin of low-frequency THz resonances. It has been observed that the lowest THz resonances (< 2 THz) originate due to translation/rotation of the whole crystal structure and the resonances from 2 to 4 THz are mainly due to intermolecular hydrogen bond bending/stretching vibrations. In order to understand the individual hydrogen bond strengths, compliance constants, which are inverse of the force constants are calculated and Natural Bond Orbital (NBO) analysis has been carried out. Comparison of the experimental THz spectra of different complexes shows that there is a small but tunable variation in THz resonances from one complex to another. Tuning of THz resonances has potential applications in designing THz tags, which can be used in various anti-counterfeiting applications such as currency notes, pharmaceutical tablets. (C) 2019 Elsevier B.V. All rights reserved.

10aCompliance constant10aNatural bond orbital analysis10aOrganic molecular complex10aTerahertz spectroscopy1 aDash, Jyotirmayee1 aRay, Shaumik1 aDevi, Nirmala1 aBasutkar, Nitin1 aAmbade, Ashootosh, V.1 aPesala, Bala uhttps://library.ncl.res.in/content/fine-tuning-terahertz-resonances-hydrogen-bonded-organic-molecular-complexes