A Computational Investigation of the Substituent Effects on Geometric, Electronic, and Optical Properties of Siloles and 1,4-Disilacyclohexa-2,5-dienes

Abstract

Thirty two differently substituted siloles 1a–1p and 1,4-disilacyclohexa-2,5-dienes 2a–2p were investigated by quantum chemical calculations using the PBE0 hybrid density functional theory (DFT) method. The substituents included σ-electron donating and withdrawing, as well as π-electron donating and withdrawing groups, and their effects when placed at the Si atom(s) or at the C atoms were examined. Focus was placed on geometries, frontier orbital energies and the energies of the first allowed electronic excitations. We analyzed the variation in energies between the orbitals which correspond to HOMO and LUMO for the two parent species, here represented as ΔεHL, motivated by the fact that the first allowed transitions involve excitation between these orbitals. Even though ΔεHL and the excitation energies are lower for siloles than for 1,4-disilacyclohexa-2,5-dienes the latter display significantly larger variations with substitution. The ΔεHL of the siloles vary within 4.57–5.35 eV (ΔΔεHL = 0.78 eV) while for the 1,4-disilacyclohexa-2,5-dienes the range is 5.49–7.15 eV (ΔΔεHL = 1.66 eV). The excitation energy of the first allowed transitions display a moderate variation for siloles (3.60–4.41 eV) whereas the variation for 1,4-disilacyclohexa-2,5-dienes is nearly doubled (4.69–6.21 eV). Cyclobutadisiloles combine the characteristics of siloles and 1,4-disilacyclohexa-2,5-diene by having even lower excitation energies than siloles yet also extensive variation in excitation energies to substitution of 1,4-disilacyclohexa-2,5-dienes (3.47–4.77 eV, variation of 1.30 eV).

Tuning the Optoelectronic Properties of Stannoles by the Judicious Choice of the Organic Substituents

“…However, using σ*-π*-conjugation as a means for lowering the HOMO-LUMO gap is much less common; this phenomenon can be observed by formally substituting the sp 3 Since then, investigations of different synthetic routes [19][20][21] and studies of the (opto-) electronic properties, [22][23] aromaticity 24 and reactivity were conducted for the related siloles, [25][26][27] but germoles, [28][29] stannoles 30 and plumboles [31][32] are much less well investigated. 33 However, the study of such heterocycles is of great interest, since they themselves or their ring fused analogs [34][35][36][37][38][39][40] show great potential in organic electronic devices.…”

The Combination of Cross‐Hyperconjugation and σ‐Conjugation in 2,5‐Oligosilanyl Substituted Siloles

“…As structural indicators of both, σ‐ and π‐conjugation, we have compared the lengths of the exocyclic Si−C single bonds and of the ring C=C double bonds as well as the R‐Si‐C angles of siloles 2 – 4 (Figure 6). Electron delocalization between the substituents in the 2,5‐positions and the silole core generally leads to a shortening of single bonds and elongation of double bonds [7] . As it is shown in Table 2, change of the substituent R (as represented in Figure 6) in the 2,5‐positions leads neither to elongation of the C=C double bond (7(C=C)) of the silole ring nor to a shortening of the exocyclic Si−C single bond (3 (Si−C)).…”

“…Electron delocalization between the substituents in the 2,5-positions and the silole core generally leads to as hortening of singleb onds and elongationo fd ouble bonds. [7] As it is shown in Ta ble 2, change of the substituent R (as represented in Figure 6) in the 2,5-positions leads neither to elongation of the C=Cd ouble bond (7(C=C)) of the silole ring nor to as hortening of the exocyclic SiÀCs ingleb ond (3 (SiÀC)). However,t he R-Si-C bond angle a calculated for tris-(trimethylsilyl)silyl-substituteds ilole 3 is widened from values typical for sp 3 hybridization of the carbon atom to values closert osp 2 hybridization.…”

“…Typically,t his expression refers to organic p-conjugated compounds, where sp 2 -hybridized carbon atoms in ac o-planar arrangementl ead to the formation of an extended p-system. Apart from plain p-conjugation of alternating multiple bonds, other types of conjugation are known such as that of cross-hyperconjugation [1,2] present in siloles and related molecules [3][4][5][6][7] and that of s-conjugation, which is known forpolysilanes and other catenatedheavy group 14 elements (Figure1). [3,8] It is also known that different types of conjugation can be combined, and phenyls ubstituted siloles and polysilanes can be considered as examples of mixed p-conjugation/cross-hyperconjugation and p-conjugation/s-conjugation, respectively.…”

Stability and semi‐conductive property of some derivatives of mono‐and di‐silole: A theoretical study

“…[5][6][7][8][9] Furthermore, substituents at the ring Si atom in some silole derivatives have been studied by Aleksandra V. Denisova and his co-workers. [10] The analysis of the variation in energies between HOMO and LUMO presented that the HOMO-LUMO gap of the silole derivatives can be varied in the range 4.57 to 5.35 eV. To further investigate the effects of 1-substituents on silole, we have studied two kinds of substituents.…”