Electronic Structure of the Ground and Excited States of β-Carboline

• Published in: Chemphyschem Vol. 9; no. 6; pp. 896 - 901
• Main Authors: Pérez Mondéjar, Vicente, García Cuesta, Inmaculada, Lazzeretti, Paolo, Sánchez-Marín, José, Sánchez de Merás, Alfredo
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 21.04.2008; WILEY‐VCH Verlag; Wiley
• Subjects: Ab initio calculations; aromaticity; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Carbolines - chemistry; Coupled cluster theory; electronic structure; Electronic structure of atoms, molecules and their ions: theory; Electrons; Exact sciences and technology; excited states; Magnetics; Models, Molecular; Molecular Structure; nitrogen heterocycles; Physics; Spectrum Analysis; Aromaticity; Nitrogen heterocycle; Theoretical study; Singlet state; Excited states; Electron correlations; Electronic structure; Carboline derivatives; Transition energy; Oscillator strengths; nitrogen heterocycles; Ab initio calculations; Coupled cluster method; Organic compounds; Solvent effects
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200700750

Coupled‐cluster calculations are used to compute the energy of conversion between the neutral and the zwitterionic forms of β‐carboline. The stability of the different species is discussed in terms of charge separation and aromatic character, which is related to magnetic criteria. By means of a linear response formalism the vertical excitation energies and oscillator strengths of the lowest singlet states of both structures as well as of the cationic species are determined. General agreement of the relative position and intensity of the different peaks with experimental data is achieved, but the overall spectra are slightly displaced because of solvent effects. Stable species? The most stable form of β‐carboline (see picture; C yellow, H white, N light blue) is the neutral species, both in polar solvents and in vacuo, although the zwitterionic conformation is the most aromatic according to ab initio calculations of magnetic criteria and coupled‐cluster excitation energies.