3.1. Geometries
Fig. 2 depicts the chemical structure of parent molecular DTSand its synthetic derivatives 1-9 that belong to the class of
monomer; whereas two compounds 10-11 have fallen into the
categorical dimer with/without the bridge. All were selected from
several previous works of literature and have been identified as
synthetic compounds [4,8,11,15-17]. The optimized geometrical
structures of studied systems are shown in Figs. 3 and Fig. S1,
including four states of neutral, cation, anion and S1.
Meanwhile, the selective bond lengths/bond angles are tabulated in Table
S1. The most striking feature is that not only previous calculations,
but synthetic outcomes also confirmed that siloles presented in both
planar, twist intramolecular transfer, and J-aggregate formations
[4,8,18]. In all four states, the computational DFT method points
out that the optimized planarity or co-planarity are observed for the
compounds 5 and 10 . It is well known that the more
co-planar the structures of all compounds are in the S1 state, the
faster the transfer of the photo-induced electron from S0 to S1.(19)
However, the dihedral angle θS-C4”-C4”-C3” in
flexible thiophene bridge of compound 11 shows that the values
of 74.7o/neutral form, 31.4o/anion,
27.8o/cation, and
13.3o/S1. This suggests that molecule11 has lost the co-planarity in the S1 state (Table S2).
We found that parent DTS and its analogs 1-5 have an
equation in bond distances between C1-C2 and C1’-C2’ in each compound.
These compounds also contain a C2 axis going
through bond C4-C4 and the silicon atom, while compound 11possesses a C2 axis between C4”-C4”. ACi center has been observed via C1’-C1’ in
DTS-DTS typical compound 10 [8]. The symmetrical property
is further identified by means of electronic indices. For instance,
compound 10 is comprised of the definite dipole moment of 0.00
Debye and is much lower than that of the bulky asymmetrical one of
compound 11 (3.876 Debye) (Table 1).
Having a detailed analysis, from all studied compounds, C1-C2 and/or
C1’-C2’ bond lengths of a typical neutral and anion appear to be
consistently shorter than those of S1 and cation in each
compound. Similarly, the values of C4-C4 and/or C4-C4’ bond distances in
neutral mostly generate longer outcomes than those of the anion, cation
and S1 forms. For dimeric compounds 10 and 11 , it can
be seen from Table S3 that the structure of compound 10 is more
planar than compound 11 in both states. It is interesting to
note that for all compound which have substutient SMe (compounds3 , 6 , 8 , 9 , 10 ), the methyl
groups of terminal methylthio moieties are almost perpendicular with the
DTS units in the neutral, anion, and S1 states, and mostly
planarization/co-planarization is found in cation ones. Because the more
relaxation in structure between the neutral and cation form of these
compounds can lead to the lager hole reorganization energy so these
molecules will show the lager the λh than other
compounds (as will be discussed later). The distortion in bond/dihedral
of the compound 11 is lager than other compounds, which
increase the reorganization energy of this compound.