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Titolo:
EXCITED-STATES OF THE PHTHALIMIDE CHROMOPHORE AND THEIR EXCITON COUPLINGS - A TOOL FOR STEREOCHEMICAL ASSIGNMENTS
Autore:
GAWRONSKI J; KAZMIERCZAK F; GAWRONSKA K; RYCHLEWSKA U; NORDEN B; HOLMEN A;
Indirizzi:
ADAM MICKIEWICZ UNIV POZNAN,DEPT CHEM PL-60780 POZNAN POLAND CHALMERS UNIV TECHNOL,DEPT PHYS CHEM S-41296 GOTHENBURG SWEDEN
Titolo Testata:
Journal of the American Chemical Society
fascicolo: 46, volume: 120, anno: 1998,
pagine: 12083 - 12091
SICI:
0002-7863(1998)120:46<12083:EOTPCA>2.0.ZU;2-R
Fonte:
ISI
Lingua:
ENG
Soggetto:
DIFFERENTIAL-OVERLAP TECHNIQUE; TRANSITION-METAL COMPLEXES; INTERMEDIATE NEGLECT; CIRCULAR-DICHROISM; SPECTROSCOPY; SPECTRA; MOLECULES;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
59
Recensione:
Indirizzi per estratti:
Citazione:
J. Gawronski et al., "EXCITED-STATES OF THE PHTHALIMIDE CHROMOPHORE AND THEIR EXCITON COUPLINGS - A TOOL FOR STEREOCHEMICAL ASSIGNMENTS", Journal of the American Chemical Society, 120(46), 1998, pp. 12083-12091

Abstract

The electronically excited states of the phthalimide chromophore havebeen studied by means of linear dichroism (LD) of samples partially oriented in poly(vinyl alcohol) films, magnetic circular dichroism (MCD), and circular dichroism (CD) spectroscopy. On the basis of the LD measurements, the low-energy tail (340-320 nm) of the first absorption band is assigned to an out-of-plane polarized pi-->pi transition (I). At higher energy, the electronic spectrum is resolved into contributions from five pi-->pi transitions: II(300 nm, long-axis polarized), III (275 nm, short-axis polarized), IV (235 nm, short-axis polarized), V(220 nm, long-axis polarized), and VI (similar to 210 nm, short-axis polarized). The results from semiempirical (INDO/S-CI) and ab initio (CIS/6-31+G(d)) MO calculations compare well with the proposed assignments of the excited states. Degenerate exciton interaction between electric-dipole-allowed transitions of two phthalimide chromophores is observed in the electronic absorption spectra of the achiral bis-phthalimides 2a-c and in the CD spectrum of the chiral bis-phthalimide 3a. Forthe latter compound, the solid-state geometry has been determined by X-ray diffraction analysis. Good agreement between experimental and computed CD spectra confirms that the coupled-oscillator exciton model provides the basis for a reliable nonempirical method for the assignment of absolute configuration for this class of compounds. Nondegenerateexciton coupling between phthalimide and benzoate or phenyl chromophores is born out in the CD spectra of homochiral molecules 3c and 3d with the rigid cyclohexane skeleton. Finally, the exciton coupling method is used to make stereochemical assignments for the acyclic, conformationally flexible derivatives 4a-c and 5b.

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Documento generato il 01/10/20 alle ore 15:22:31