Manifestations of Conformational Defects in Electronic Spectra of Polysilanes – a Theoretical Study

Abstract

Summary In this paper, density functional theory (DFT) and time dependent DFT (TDDFT) are applied on the calculation of electronic properties of alkyl‐ and aryl‐substituted oligosilanes with conformational defect introduced into their silicon chain. Oligo[methyl(phenyl)silane]s and oligo(dimethylsilane)s up to 10 or 13 mer units, respectively, are treated as model structures by DFT and TDDFT with B3LYP/6–31 G* base. Frontier molecular orbital (FMO) energies evince the dependence on the presence as well as on the position of the defect in oligomer backbones. Delocalization of FMO is strongly influenced by position of the defect which in some cases divides the molecule to the FMO‐rich part and the part almost without FMO delocalization and therefore affects location of electrons. Behaviour of longer chains in analogous polysilanes is deduced from linear regression of plots of FMO energy over the inverse of the polymerization degree.

Effect of backbone conformation and its defects on electronic properties and assessment of the stabilizing role of π–π interactions in aryl substituted polysilylenes studied by DFT on deca[methyl(phenyl)silylene]s

“…The backbone end atoms were capped with methyl groups and calculation was set in vacuum with no constrained bonds or angles. OMPSi 10 with approximately transoid conformation was obtained as can be also found in our previous work [ 20 ]. This optimal structure was used for virtual preparation of other OMPSi 10 analogues with a kink, which represents a conformational defect.…”

“…Such bend can be regarded as conformational defect because it disrupts regular σ-delocalization and therefore influences final polysilylene properties [ 18 , 19 ]. This defect was defined as a gauche -kink in the backbone and described on oligo-DMSi n (ODMSi) and oligo-MPSi n (OMPSi) with n = 1–10 by density functional theory (DFT) in our previous work, where the kink influence on the electronic properties of oligosilylenes was confirmed [ 20 ]. The change has been clearly manifested in absorption spectra plots, where hypsochromic shift of the main absorption band had been detected.…”

Thickness dependent structural ordering, degradation and metastability in polysilane thin films: A photoluminescence study on representative σ-conjugated polymers

“…Although the presented study is based on only yet superiorly powerful PL study, it may invoke a revision of the recent knowledge on thin film structure with thickness range from tens to thousands nanometers using both experimental and theoretical [42] approaches. We believe that our observations may be very helpful not only in the field of σ-conjugated PSis but also for much broader scientific interest given to π-conjugated polymers and that the correlation between the thickness and microstructure ergo optoelectronic properties of various π-conjugated polymers will be elucidated in the near future while seeing first achievements so far.…”