Electronic excitations of 1,4-disilyl-substituted 1,4-disilabicycloalkanes: A MS-CASPT2 study of the influence of cage size
2007 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 14, 2804-2810 p.Article in journal (Refereed) Published
We present a multistate complete active space second-order perturbation theory computational study aimed to predict the low-lying electronic excitations of four compounds that can be viewed as two disilane units connected through alkane bridges in a bicyclic cage. The analysis has focused on l,4-disilyl-l,4-disilabicyclo[2.2.1]heptane (la), l,4-bis(trimethylsilyl)-l,4- disilabicyclo[2.2.1]heptane (1b), l,4-disilyl-l,4-disilabicyclo[2.1.1]hexane (2a), and l,4-fcw(trimethylsilyl)-l,4-disilabicyclo[2.1.1]hexane (2b). The aim has been to find out the nature of the lowest excitations with significant oscillator strengths and to investigate how the cage size affects the excitation energies and the strengths of the transitions. Two different substituents on the terminal silicon atoms (H and CH3) were used in order to investigate the end group effects. The calculations show that the lowest allowed excitations are of the same character as that found in disilanes but now redshifted. As the cage size is reduced from a 1,4-disilabicyclo[2.2.1]heptane to a l,4-disilabicyclo[2.1.1]hexane, the Si'"Si through-space distance decreases from approximately 2.70 to 2.50 A and the lowest allowed transitions are red-shifted by up to 0.9 eV, indicating increased interaction between the two Si-Si bonds. The first ionization potential, which corresponds to ionization from the Si-Si a orbitals, is lower in Ib and 2b than in SiiMee by approximately 0.9 and 1.2 eV, respectively. Moreover, Ib and 2b, which have methyl substituents at the terminal Si atoms, have slightly lower excitation energies than the analogous species la and 2a.
Place, publisher, year, edition, pages
2007. Vol. 111, no 14, 2804-2810 p.
IdentifiersURN: urn:nbn:se:uu:diva-95451DOI: 10.1021/jp070010nISI: 000245438600021PubMedID: 17388376OAI: oai:DiVA.org:uu-95451DiVA: diva2:169661