1. Introduction
Organic semiconductors (OSCs) refers to both π-conjugated polymers and
semiconductors [1]. Currently, OSCs are available as well as a
viable commercial alternative to traditional organic and inorganic
materials. Several typical observations, such as light-emitting diodes
(OLEDs), organic effect transistors (OFETs), photovoltaic cells (OPVs),
and sensors are directly related to OSCs [2,3]. The molecular
designation is the best way to make the possibility of tuning the
conductivity, low-temperature processability, flexibility, diverse
colors, and low-cost effective of OSCs materials. In materials science,
siloles-based OSCs have received much more attention because of their
unique optical and electrochemical characteristics [4]. Silole
(silacyclopentadiene) can be defined as a ring system which contains
silicon σ*-orbital interacted
with π*-orbital of butadiene fragment, lowered the
LUMO energy level, and reduced the
ELUMO-HOMO (Egap) [5]. As shown in
Fig. 1, after calculating at B3LYP/6-311G(d,p) level, the silole shows a
smaller band gap (4.896 eV) than that of the same hetero-compound.
Particularly, dithienosilole (DTS ) not only have a smaller band
gap when compared to silole but also has a smaller one (4.043 eV) among
the fused bithiophene systems. In addition, the fused bithiophene
typical siloles not only have associated with the properties of high
conjugation, planarity, and rigidity, they are more flexible in the
tuning structure than regular silole [6,7]. Due to lowered LUMO
level, DTS and related compounds stabilized in the air, and
possessed high electron mobility, thereby being suitable for electron
transport materials and emitter in OLEDs [1]. Hence, we scrutinize
DTS based molecules for optoelectronic function. The introduction of
saturated and/or unsaturated functional groups on thiophene ring,
especially in terms of 1,1’-positions, have directly affected the
character of materials. Taking the structure of
ITO/TPD/Alq3/DTS(Py)2/Mg–Ag as an example, this
electroluminescent (EL) device emitted a strong green light with a high
luminance of 16000 cd/m2 because of the effects of
electron-withdrawing pyridyl groups at 1,1’-positions [4,8]. The
vacuum-deposited film was made of 1-tricynanoethenyl DTS which
showed vapor chromic behaviors when in contact with organic solvent
vapors [4]. Within the large uses, DTS derivatives were
historically mostly focused on synthesizing, but extensive quantum
scientific rationales might be limited.
To date, no specific theoretically useful account has been reported. In
this paper, we aim to provide insight, using means of density functional
theory (DFT) and time dependent DFT (TD-DFT) to understand the role of
selective DTS molecules as promising candidates in OLED
materials. The objectives of this work are in the scope of assessments
of analytical electronic structures, optoelectronic aspects, and
structure-property relationship, regarding fourteen previous synthetic
parent molecular DTS and its eleven derivatives 1-11and four new designated analogs.