Collect. Czech. Chem. Commun. 2011, 76, 2085-2116
Published online 2012-02-03 09:45:13

Why do disilanes fail to fluoresce?

Matthew K. MacLeoda and Josef Michla,b,*

a Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA
b Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo nám., 2, 166 10 Prague 6, Czech Republic


In contrast to longer peralkylated oligosilanes, many of which fluoresce efficiently, disilanes and trisilanes exhibit no detectable fluorescence even at low temperatures. This is especially striking in the case of disilanes, whose S1-S0 transition is quite strongly allowed, and which must have very efficient electronic excited state deactivation mechanisms. To identify them, we examine the lowest excited singlet state potential energy surface S1 of Si2Me6 with TDDFT (B3LYP/TZVP, PBE0/TZVP and BHLYP/TZVP) and ab initio (RICC2/TZVP and RIADC(2)/TZVP) methods and identify several shallow minima and nearby funnels. Relaxed excited state structures show strong valence rehybridization relative to the ground state, allowing optimal accomodation of the simultaneous presence of a negative and a positive charge in their Lewis structures. Efficient decay pathways and relations to longer oligosilanes are discussed.

Keywords: Excited states; Relaxed excited state; Excited state potential energy minima; Rydberg; Conical intersection; Funnel; Molecular orbitals; Artificial charge transfer; Disilane; Hypervalent Si; Excitation localization; TDDFT; RICC2; RIADC(2).

References: 58 live references.