UV, MCD, and LD spectra of a conformationally constrained ortho-tetrasilane: Support for the avoided crossing model of conformational effects on excited states

Citation
H. Tsuji et al., UV, MCD, and LD spectra of a conformationally constrained ortho-tetrasilane: Support for the avoided crossing model of conformational effects on excited states, J PHYS CH A, 105(45), 2001, pp. 10246-10248
Citations number
33
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY A
ISSN journal
1089-5639 → ACNP
Volume
105
Issue
45
Year of publication
2001
Pages
10246 - 10248
Database
ISI
SICI code
1089-5639(20011115)105:45<10246:UMALSO>2.0.ZU;2-8
Abstract
UV absorption,. magnetic circular (MCD), and linear (LD) dichroism of an n- tetrasilane configurationally constrained to the ortho conformation (calcul ated SiSiSiSi dihedral angle omega similar or equal to 95 degrees) are repo rted, and the results are compared with them theoretical expectation of fou r low-energy transitions. Two strong UV absorption maxima with similar inte nsity and positive MCD B terms are assigned to states of B symmetry. A thir d calculated transition to an 2(1)A state was clearly detected in the LD sp ectrum, but a calculated weak transition to a 3(1)A state at a higher energ y was not observed. The results support a previous rationalization of the c onformational properties of the n-tetrasilane chromophore, according to whi ch one of two low-energy transitions into B-symmetry states is of sigma sig ma* and the other of sigma pi* type in the planar cis and anti limits, and they undergo a strongly avoided crossing as co changes from 0 degrees to 18 0 degrees, keeping their energies nearly constant but interchanging their o scillator strengths.