The benzothiadiazole moiety has been extensively exploited as a building block in the syntheses of efficient organic semiconducting materials during the past decade. In this paper, parallel synthetic routes to benzothiadiazole derivatives, inspired by previous computational findings, are reported. The results presented here show that various C-C cross-couplings of benzothiadiazole, thiophene, and thiazole derivatives can be efficiently performed by applying Xantphos as a ligand of the catalyst system. Moreover, improved and convenient methods to synthesize important chemical building blocks, e.g., 4,7-dibromo-2,1,3-benzothiadiazole, in good to quantitative yields are presented. Additionally, the feasibility of Suzuki-Miyaura and direct coupling methods are compared in the synthesis of target benzothiadiazole derivatives. The computational characterization of the prepared benzothiadiazole derivatives shows that these compounds have planar molecular backbones and the possibility of intramolecular charge transfer upon excitation. The experimental electrochemical and spectroscopic studies reveal that although the compounds have similar electronic and optical properties in solution, they behave differently in solid state due to the different alkyl side-group substitutions in the molecular backbone. These benzothiadiazole derivatives can be potentially used as building blocks in the construction of more advanced small molecule organic semiconductors with acceptor-donor-acceptor motifs.

Multi-state effects should be considered when calculating electronic couplings at local polymer–fullerene interfaces with the non-tuned and optimally tuned long-range corrected functionals.

Here, we investigate the effects of both tuning the range-separation parameter of long-range corrected (LRC) density functionals and including dispersion corrections on describing the local optoelectronic properties of polymer-fullerene interfaces that are critical to the performance of polymer solar cells (PSCs). Focusing on recently studied (Chen, et al., Chem. Mater., 2012, 24, 4766-4772) PSC active layers derived from poly(benzodithiophene-co-quinoxaline) and substituted fullerene PCBM, we compare the performance of global hybrid functionals (B3LYP and B3LYP-D) alongside two LRC functionals (ωB97X and ωB97X-D) and their optimally tuned (OT) analogs (OT-ωB97X and OT-ωB97X-D). Our results confirm that OT-LRC functionals generally improve the description of the optical properties of the individual materials with respect to experiment. For electron-donor (eD)-electron-acceptor (eA) complexes used to describe the local optoelectronic properties of the material interface, PCBM is found to preferentially settle near the quinoxaline acceptor units on the copolymer backbone, regardless of the functional, though dispersion corrections have a strong influence on the intermolecular distances and, in turn, the nature of the excited states. All functionals yield very similar descriptions of the transition maxima for the complexes, i.e. predominant local excitations on the copolymer. Importantly, tuning the range-separation parameter of the LRC functional is shown to have a profound effect, as the OT functionals allow for the description of the charge transfer states of the eD-eA complexes, while the non-tuned LRC functionals predict only local intramolecular excitations. These results hold considerable importance for deriving the appropriate physical understanding of the interfacial structure-property-function relationships of PSCs.

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...

Water existing within thin polyelectrolyte multilayer (PEM) films has significant influence on their physical, chemical, and thermal properties, having implications for applications including energy storage, smart coatings, and biomedical systems. Ionic strength, salt type, and terminating layer are known to influence PEM swelling. However, knowledge of water's microenvironment within a PEM, whether that water is affiliated with intrinsic or extrinsic ion pairs, remains lacking. Here, we examine the influence of both assembly and post-assembly conditions on the water−ion pair interactions of poly(styrene sulfonate)/ poly(diallyldimethylammonium) (PSS/PDADMA) PEMs in NaCl and KBr. This is accomplished by developing a methodology in which quartz crystal microbalance with dissipation monitoring is applied to estimate the number of water molecules affiliated with an ion pair (i), as well as the hydration coefficient,. PSS/PDADMA PEMs are assembled in varying ionic strengths of either NaCl and KBr and then exposed post-assembly to increasing ionic strengths of matching salt type. A linear relationship between the total amount of water per intrinsic ion pair and the post-assembly salt concentration was obtained at post-assembly salt concentrations >0.5 M, yielding estimates for both i and π salt H 2 O . We observe higher values of i and π salt H 2 O in KBr-assembled PEMs due to KBr being more effective in doping the assembly because of KBr's more chaotropic nature as compared to NaCl. Lastly, when PSS is the terminating layer, i decreases in value due to PSS's hydrophobic nature. Classical and ab initio molecular dynamics provide a microstructural view as to how NaCl and KBr interact with individual polyelectrolytes and the involved water shells. Put together, this study provides further insight into the understanding of existing water microenvironments in PEMs and the effects of both assembly and post-assembly conditions.

Conjugated donor-acceptor (D-A) copolymers show tremendous promise as active components in thin-film organic bulk heterojunction solar cells and transistors, as appropriate combinations of D-A units enable regulation of the intrinsic electronic and optical properties of the polymer. Here, the structural, electronic, and optical properties of two D-A copolymers that make use of thieno[3,4-c]pyrrole-4,6-dione as the acceptor and differ by their donor unit-benzo[1,2-b:4,5-b']dithiophene (BDT) vs the ladder-type heptacyclic benzodi(cyclopentadithiophene)-are compared using density functional theory methods. Our calculations predict some general similarities, although the differences in the donor structures lead also to clear differences. The extended conjugation of the stiff ladder-type donor destabilizes both the highest occupied and lowest unoccupied molecular orbital energies of the ladder copolymer and results in smaller gap energies compared to its smaller counterpart. However, more significant charge transfer nature is predicted for the smaller BDT-based copolymer by natural transition orbitals than for the ladder copolymer. That is, the influence of the acceptor on the copolymer properties is "diluted" to some extent by the already extended conjugation of the ladder-type donor. Thus, the use of stronger acceptor units with the ladder-type donors would benefit the future design of new D-A copolymers.

No abstract

Achieving water-induced shape-memory property in poly(D,L-lactide) (PDLLA), generated by means of advanced processing methods, opens possibilities to develop novel bioresorbable medical devices with shape-memory properties activated by the human body without external heat. The main phenomena that affect the molecular movements that enable the water-induced shapememory effect in an oriented PDLLA in an aqueous environment at physiological temperature are related to the water driven disruption of the intermolecular dipole-dipole and/or hydrogen bonding of the oriented PDLLA chains and the subsequent decrease of the glass transition temperature (T g ) to the range of physiological temperature. The diffused water in the polymer matrix decreased the energy needed to finish the glass transition process explaining the higher shape-recovery rate of the c-irradiated PDLLA with respect to the non-c-irradiated PDLLA in an aqueous environment at physiological temperatures. The water-induced decrease in the T g was thermally reversible. The efficacy of the generated shape-memory was tested with PDLLA shape-memory nails in a pullout test, in which the pullout force of the PDLLA nails increased 360% during a seven day test period in vitro at 37