Highlights•Novel D-A and A-D-A type small molecule electron donors were synthesized •Characterization by computational, electrochemical, and spectroscopic methods •A-D-A type materials were tested as active layer components in OSC devices •Relations between molecular structures and properties are studied and discussed Abstract Efficient synthetic methods for carbazole-based small molecule electron donors with donoracceptor (D-A) and A-D-A type structures were developed. In order to study the relation between chemical structures and material properties, the prepared compounds were characterized in detail using absorption spectroscopy, differential pulse voltammetry, and computational methods. In addition, symmetrical A-D-A type compounds were tested as an active layer component in bulk heterojunction based organic solar cell (OSC) devices with conventional structure. The results show that the two compound types have many similar properties. However, the extended molecular structure of A-D-A type compounds offer better film forming properties and higher molar absorption coefficients compared with the D-A type materials. Furthermore, the attachment of fluoro substituents in the A units has a positive effect on all solar cell device parameters. Moreover, the computational studies revealed that the molecular structures are twisted between the central carbazole D unit and -bridge which may result in inefficient intramolecular charge transfer and, also, relatively limited short-circuit currents in OSC devices.Recently, we reported a synthetic pathway to BT-based building blocks [27]. Since then, we have further developed the synthetic strategy and, here, we present the syntheses of two unsymmetrical D-A and two symmetrical A-D-A type small molecules. In these compounds, Cz acts as a D unit and either BT or its fluoro-substituted derivative as an A unit. Thiophene and thiazole have been used as a -bridge in between the D and A units. In order to find out how the changes in molecular structures affect the material properties, the prepared D-A and A-D-A type small molecule compounds have been characterized by spectroscopic, electrochemical, and computational methods.Moreover, the symmetrical A-D-A type compounds have been tested as electron donor materials in BHJ-based OSC devices. Experimental sectionCommercial reagents were used as received. 2-(3-Hexylthiophen-2-yl)-5-(4,4,5,5tetramethyl-1,3,2-dioxaborolan-2-yl)thiazole and compound 3b were synthesized using the previously published methods [27]. The chemical structures of new compounds were characterized by using NMR and HRMS techniques. Melting points (reported as peak values) of compounds 5a, 5b, 6a, and 6b were measured by using Mettler Toledo DSC 1 apparatus with a TSO800GC1 Gas Control system. Samples of 1.6-2.2 mg were placed in 40 L Al crucibles with pierced lids. The DSC scans were carried out from 5 o C to 300 o C at the heating rate of 20 o C min -1 under a nitrogen flow of 60 mL min -1 . Syntheses2.1.1. Synthesis of 4-bromo-5-fluoro-7-(5-hexylthiophen-2-yl...

Dithienosilole moiety is an electron donating unit, and it has been applied, for example, as a part of small molecular and polymeric electron donors in high performance organic photovoltaic cells. Herein, we report efficient synthetic routes to two symmetrical, dithienosilolo-central-unit-based A-D-A type organic semiconducting materials DTS(Th 2 FBTTh) 2 and DTS(ThFBTTh) 2 . Fine-tuned conditions in Suzuki–Miyaura couplings were tested and utilized. The effect of inserting additional hexylthiophene structures symmetrically into the material backbone was investigated, and it was noted that contrary to commonly accepted fact, the distance between electron donor and acceptor seems to play a bigger role in lowering the E gap value of the molecule than just extending the length of the conjugated backbone. We searched for precedent cases from the literature, and these are compared to our findings. The optical properties of the materials were characterized with UV–vis spectroscopy. Majority of the intermediate compounds along the way to final products were produced with excellent yields. Our results offer highly efficient routes to many heterocyclic structures but also give new insights into the design of organic semiconducting materials.