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.