A C Rajan, M R Rezapour, J Yun, Y Cho, W J Cho, S K Min, G Lee, K S Kim; ACS Nano 8 (2), 1827-1833, 11 (2014).

Laser-driven molecular spectroscopy of low spatial resolution is widely used, while electronic current-driven molecular spectroscopy of atomic scale resolution has been limited because currents provide only minimal information. However, electron transmission of a graphene nanoribbon on which a molecule is adsorbed shows molecular fingerprints of Fano resonances, i.e., characteristic features of frontier orbitals and conformations of physisorbed molecules. Utilizing these resonance profiles, here we demonstrate two-dimensional molecular electronics spectroscopy (2D MES). The differential conductance with respect to bias and gate voltages not only distinguishes different types of nucleobases for DNA sequencing but also recognizes methylated nucleobases which could be related to cancerous cell growth. This 2D MES could open an exciting field to recognize single molecule signatures at atomic resolution. The advantages of the 2D MES over the one-dimensional (1D) current analysis can be comparable to those of 2D NMR over 1D NMR analysis. link

M R Rezapour, A C Rajan, K S Kim; J. Comput. Chem. 35 (26), 1916-1920, 1 (2014)

In molecular electronics, the conductance strongly depends on the frontier energy levels and spatial orientations of molecules. Utilizing these features, we investigate the electron transport characteristics of conjugated molecules attached on an armchair graphene nanoribbon. The resulting sharp reduction in the transmission which represents molecular fingerprints and the change of the transmission depending on the molecular orientation, are examined in accordance with a unified picture of the Fano–Anderson model. These characteristics, being unique for each molecule, would be applicable to molecular recognition and configurational analysis. link

S Thomas, A C Rajan, M R Rezapour, K S Kim; J. Phys. Chem. C 118 (20), 10855-10858, 1 (2014).

We analyze the transmission of narrow semiconducting nanoribbons designed from two-dimensional (2D) layered materials such as graphene, silicene, hexagonal boron nitride (hBN), and molybdenum disulfide (MoS2). The Fano resonance driven dips in the transmission, when nucleobases stack with graphene nanoribbon, are known to be useful for DNA sequencing. For graphene and hBN nanoribbons the transmission dips are distinct for each nucleobase, but with a larger band gap for the latter case. For silicene nanoribbon the dips due to different nucleobases are somehow less clear. The transmission of the MoS2 nanoribbon is unpromising for DNA sequencing as the dip in the transmission is not useful to identify any of the nucleobase. The dip positions in the transmission shift linearly with bias voltage. This shift depends on the nanoribbon used and the orientation of the DNA base. Hence, edge-modified hBN nanoribbons with a reduced band gap could be an alternative to graphene nanoribbon (GNR) for DNA sequencing and recognition of other adsorbents. link

M Kolaski, C R Arunkumar, KS Kim; J. Chem. Theor. and Comput. 9 (1), 847-856, 4 (2012).

Excited dimers (excimers) formed by aromatic molecules are important in biological systems as well as in chemical sensing. The structure of many biological systems is governed by excimer formation. Since theoretical studies of such systems provide important information about mutual arrangement of aromatic molecules in structural biology, we carried out extensive calculations on the benzene excimer using EOM-CCSD, RI-CC2, CASPT2, and TD-DFT approaches. For the benzene excimer, we evaluate the reliability of the TD-DFT method based on the B3LYP, PBE, PBE0, and ωPBEh functionals. We extended the calculations to naphthalene, anthracene, and pyrene excimers. We find that nearly parallel stacked forms are the minimum energy structure. On the basis of the benzene to pyrene excimers, we might roughly estimate the equilibrium layer-to-layer distance for bilayer-long arenes in the first singlet excited state, which is predicted to be bound. link