Showing papers on "Pi interaction published in 1983"
15 May 1983
TL;DR: In this paper, the ET spectra of monosubstituted benzenes containing the −OH, −OCH 3, −OC(CH 3 ) 3, −SH, −SCH 3 and −SC(CH3 ) 3 derivatives were analyzed and the electron affinity of the LUMO π* 2a 2 is close to that of benzene.
Abstract: The ET spectra of monosubstituted benzenes containing the −OH, −OCH 3 , −OC(CH 3 ) 3 , −SH, −SCH 3 , −SC(CH 3 ) 3 and −NHCH 3 groups show that in the non-hindered nitrogen and oxygen derivatives the lone pair/π* interaction produces a significant destabilization of the ring 4b 1 π* MO, while the electron affinity (EA) of the LUMO π* 2a 2 is close to that of benzene. The stabilization of the empty π* MOs produced by the sulphur-containing substituents demonstrates the presence of interacting empty orbitals localized at the substituent. The stabilizing effect of these orbitals does not change significantly with the σ framework of the substituent nor with its torsional angle around the S-ring bond. This is consistent with the S 3d character of the stabilizing orbitals. The EA increase of the LUMO in the rotated −SC(CH 3 ) 3 derivative is mainly ascribed to the reduced interaction between the S lone-pair orbital and the 4b 1 π* MO, and, in part, to σ*/π* interaction.
35 citations
25 citations
TL;DR: In this article, the first two substituents perturb the energies of the outer filled π orbitals and of the empty π* orbitals in opposite directions, causing a reduction of the HOMO/LUMO energy separation.
15 citations
TL;DR: In this article, the nature of the lowest energy triplet state of PNA, N, N-dimethyl-p-nitroaniline (DMPNA), and NB was examined using the semi-empirical CNDO/S-CI method with selected parameter options.
Abstract: The nature of the lowest energy triplet state (T
1) ofp-nitroaniline (PNA), N,N-dimethyl-p-nitroaniline (DMPNA) and nitrobenzene (NB) is reexamined using the semiempirical CNDO/S-CI method with selected parameter options. The present results indicate that in the case of theunperturbed molecules the short-axis polarized π* ←n(π) triplet largely localized at the acceptor end of the molecule may lie lower in energy than the triplet manifold counterpart of the intense intramolecular charge-transferD
+ →A
−singlet excitation. Computations suggest, however, that polar solvents strongly stabilize the PNA and DMPNA π* ← π charge-transfer triplet relative to other excitations, whereas specific solvent hydrogen-bonded interactions stabilize the π* ←n(σ) triplet of NB below those of π* ← π character. These assignments allow a rationalization of phosphorescence lifetime data,T
n
←T
1 absorption measurements and relative photochemical behavior.
14 citations
TL;DR: The absorption and fluorescence spectra have shown that, depending on the pH of the medium, the 7-azaindolines can exist in an anionic, cationic, and a neutral form as discussed by the authors.
Abstract: 1.
The absorption and fluorescence spectra have shown that, depending on the pH of the medium, the 7-azaindolines can exist in an anionic, cationic, and a neutral form. Protonation of the pyridine nitrogen atom leads to the formation of the σ, π* state, an increase in the lifetime of the S1 (π, π*) state, and to the possibility of photodissociation through this state.
2.
In an alkaline medium the adiabatic photodissociation of 7-azaindolines takes place according to an acid mechanism, leading to the formation of an anion in the excited state.