Retaining Hückel Aromaticity in the Triplet Excited State of Azobenzene. 2022

P E Swathi Krishna, and Vivek V Dev, and Remya Ramakrishnan, and Mahesh Hariharan
School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala 695551, India.

The implication of the potential concept of aromaticity in the relaxed lowest triplet state of azobenzene, an efficient molecular switch, using elementary aromaticity indices based on magnetic, electronic, and geometric criteria has been discussed. Azobenzene exhibits a major Hückel aromatic character retained in the diradical lowest relaxed triplet state (T1 ) by virtue of a twisted geometry with partial delocalization of unpaired electrons in the perpendicular p-orbitals of two nitrogen atoms to the corresponding phenyl rings. The computational analysis has been expanded further to stilbene and N-diphenylmethanimine for an extensive understanding of the effect of closed-shell Hückel aromaticity in double-bond-linked phenyl rings. Our analysis concluded that stilbene has Hückel aromatic character in the relaxed T1 state and N-diphenylmethanimine has a considerable Hückel aromaticity in the phenyl ring near the carbon atom while a paramount Baird aromaticity in the phenyl ring near the nitrogen atom of the C=N double bond. The results reveal the application of excited-state aromaticity as a general tool for the design of molecular switches.

UI MeSH Term Description Entries
D009584 Nitrogen An element with the atomic symbol N, atomic number 7, and atomic weight [14.00643; 14.00728]. Nitrogen exists as a diatomic gas and makes up about 78% of the earth's atmosphere by volume. It is a constituent of proteins and nucleic acids and found in all living cells.
D004583 Electrons Stable elementary particles having the smallest known negative charge, present in all elements; also called negatrons. Positively charged electrons are called positrons. The numbers, energies and arrangement of electrons around atomic nuclei determine the chemical identities of elements. Beams of electrons are called CATHODE RAYS. Fast Electrons,Negatrons,Positrons,Electron,Electron, Fast,Electrons, Fast,Fast Electron,Negatron,Positron
D001391 Azo Compounds Organic chemicals where aryl or alkyl groups are joined by two nitrogen atoms through a double bond (R-N Azo Dye,Azo Dyes,Compounds, Azo,Dye, Azo,Dyes, Azo
D013267 Stilbenes Organic compounds that contain 1,2-diphenylethylene as a functional group. Stilbene,Stilbene Derivative,Stilbene Derivatives,Stilbenoid,Stilbenoids,Derivative, Stilbene,Derivatives, Stilbene

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