The modified CNDO method previously reported has been applied to the calculation of a series of monosubstituted benzenes and pyridines, namely, aniline, anilinium ion, benzonitrile, nitrosobenzene, phenol, phenoxide ion, toluene, pyridinium ion, pyridine‐N‐oxide, 1‐hydroxy‐pyridinium ion, the aminopyridines, and the cyanopyridines. The calculated values of the transition energies and corresponding oscillator strengths are in good agreement with available experimental data on the electronic spectra of these compounds. An analysis of the lower‐energy excited states by means of the calculated results suggests that there is an astonishingly small amount of charge‐transfer character associated with the observed ultraviolet bands. The calculations indicate that the changes in charge densities in going from the ground state to the lowest energy π → π* excited state can be related to the Hammett σ's for the substituents.

Use of the CNDO Method in Spectroscopy. III. Monosubstituted Benzenes and Pyridines

We present a quantum-mechanical study on the solvent effects in the structure and electronic spectra of some cationic dyes: acridine orange, proflavine, safranine, neutral red, thionine and methylene blue. The geometry optimizations were carried out with the AM1 and DFT (with B3LYP functional) methods and the theoretical spectra of the dyes under study were obtained with Zindo time-dependent methods (TD–DFT and TD–HF). The solvation methodology adopted was the integral equation formulation (IEF) version of the polarizable continuum model (PCM).

The effects of solvation in the theoretical spectra of cationic dyes

https://hal-univ-rennes1.archives-ouvertes.fr/hal-01225626/document

Organic chemistry in Titan׳s upper atmosphere and its astrobiological consequences: I. Views towards Cassini plasma spectrometer (CAPS) and ion neutral mass spectrometer (INMS) experiments in space

Die Ergebnisse von PPP-Rechnungen fur Cyanine, Merocyanine und Aminochinone stehen in guter Ubereinstimmung mit den experimentellen Elektronen- und Schwingungsspektren. Das Spektrum des 2,5-Diaminobenzochinons-1,4 mus als unter Substituenteneinflus langwellig verschobenes p-Benzochinonspektrum gedeutet werden. Auch die Ladungsverteilung dieses Diaminochinons unterscheidet sich nur sehr wenig von derjenigen des Chinons. Diese Ergebnisse stutzen die Zuordnung der IR-Spektren der Aminochinone von Draber und Wallenfels und zeigen, das in den Aminochinonen der Chinoncharakter so ausgepragt ist, das es unnotig erscheint, sie als Quadrupol-merocyanine zu formulieren.

Pariser-Parr-Pople-Rechnungen an Molekülen mit Aminogruppen

The binding of the polyaromatic guest, 3,6-diaminoacridine (Proflavine) to cucurbit[n]uril (CB[n]) where n = 6, 7 and 8 has been studied by fluorescence spectrophotometry and binding constants determined using a least squares fitting method. Titration of CB[8] into a solution of Proflavine results in a 95% decrease in fluorescence up to a CB[8] to Proflavine ratio of 2:1. From the induced fluorescence spectra a binding constant of 1.9 × 107 M− 1 was determined. When Proflavine is titrated into a solution of CB[8] a similar binding constant is calculated (1.3 × 107 M− 1). Titration of CB[6] into a solution of Proflavine yields a decrease in fluorescence of 18–20%, but no binding is observed beyond what is seen within experimental error. Finally, titration of CB[7] into a solution of Proflavine results in an increase in fluorescence (32%) and a blue-shift of the emission wavelength from 509 nm to 485 nm. From the induced fluorescence spectra a binding constant of 1.65 × 107 M− 1 was determined. From 1H NMR ...

The Host-Guest Chemistry of Proflavine with Cucurbit[6,7,8]urils

SCF CI calculation has been made on cis and trans isomers of stilbene and azo-benzene. It has been shown that the electronic spectra of trans isomer should appear at a shorter wave length than the corresponding cis isomers, although the resonance theory reverses their positions. Experimentally azobenzene agrees with the conclusions of SCF theory while stilbene is better represented by the resonance theory.

SCF CI calculation of the electronic spectra of cis and trans isomers of stilbene and azo-benzene

The interaction of several nucleosides with proflavine hemisulphate was investigated by absorption and fluorescence spectroscopy in solvents with different dielectric constants. In each case, the ground state charge transfer complex was formed (observed from the difference absorption spectra) and the formation constants were calculated using the Benesi-Hildebrand equation (H.A. Benesi and J.H. Hildebrand, J. Am. Chem. Soc., 71 (1949) 2703). Fluorescence spectroscopy ruled out the possibility of exciplex formation as no new band was observed. However, static quenching occurred within a limited range of acceptor to donor concentration ratio. The formation constants calculated were found to be higher than those observed by adsorption spectroscopy.

Studies of charge transfer interaction of nucleotides with proflavine

A purely analytical method designed to compute the two-electron integrals that appear in anab-initio calculation of the electronic structures of diatomic molecules using elliptical basis set is presented. Test calculations are successfully carried out on LiH molecule.

An analytical algorithm for the evaluation of two-electron integrals in diatomics: A test calculation with an elliptical basis set

SCF calculation with CI has been found to give a reasonable value for the longest wavelength π-π* transition in nitroso and nitro benzene if a sufficient number of configurations are taken into considerations. The applicability of this method to the case of n-π* transition is, however, of doubtful validity. For the electron density approximation of chemical reactivity simple Huckel calculation may be good enough if the parameters are carefully chosen.

Rama Basu

Papers

SCF CI calculation of the electronic spectra of cis and trans isomers of stilbene and azo-benzene

Studies of charge transfer interaction of nucleotides with proflavine

An analytical algorithm for the evaluation of two-electron integrals in diatomics: A test calculation with an elliptical basis set

SCF CI calculation of the electronic spectra of nitroso and nitro benzene

Simple Hückel calculation on triphenyl cyclopropenyl cation