Effects of Side-Chain Engineering with the S Atom in Thieno[3,2-b]thiophene-porphyrin to Obtain Small-Molecule Donor Materials for Organic Solar Cells

A unified evaluation descriptor for π-bridges applied to metalloporphyrin derivatives

Establishing the structure of porphyrins with a A-π-D-π-A configuration is one of the effective strategies to maintain their dominance and compensate shortcomings through flexible changes in fragments. In this regard, π-bridges have attracted wide attention as a parameter affecting molecular backbones, electron transfer, energy levels, absorption, and other properties. However, the essence and influence of π-bridges have not yet been confirmed. In order to satisfy the requirements of intelligent application in molecular design, this study aimed to investigate the control effect of differences in π-bridge composition (thiophene and selenophene) and connection type (single bonds, ethylenic bonds and fused) on photoelectric performance. Y6 and PC61BM were used as acceptors to build donor/acceptor (D/A) interfaces and characterize the film morphology in three dimensions. Results showed that the essence of π-bridges involves a strong bridging effect (adjusting ability) between A and D fragments rather than highlighting its own nature. The large value could obtain high open circuit voltages (VOC), large separation and small recombination rates as well as stable and tight morphology. Therefore, adjusting ability is a unified descriptor for evaluating π-bridges, and it is an effective strategy to adjust material properties and morphology. This insight and discovery may provide a new evaluation descriptor for the screening and design of π-bridges.

Carbazole and Diketopyrrolopyrrole-Based D-A π-Conjugated Oligomers Accessed via Direct C-H Arylation for Opto-Electronic Property and Performance Study

Five carbazole and diketopyrrolopyrrole-based donor-acceptor (D-A) new π-conjugated oligomers (π-COs) with gradually elongated lengths are facilely synthesized via a single pot of direct C-H arylation with merits of atom- and step-economy. The structure-property-performance correlations of these π-COs and their parent polymer are studied in detail by opto-electronic characterizations and bulk heterojunction (BHJ) organic photovoltaic (OPV) devices. It is found that the π-COs having longer lengths enable better performance in OPVs owing to the enhanced intermolecular interaction with the elongation of the conjugations. The above results not only highlight the powerful synthetic strategy here provided, but also reveal that π-COs with unique properties might find promising application in OPVs.

Amphipolar, Amphiphilic 2,4-diarylpyrano[2,3-b]indoles as Turn-ON Luminophores in Acidic and Basic Media

A versatile amphiphilic pyrano[2,3-b]indole for halochromic turn-ON luminescence in acidic or basic media is accessed by an insertion-coupling-cycloisomerization and adjusting solubilizing and phenolic functionalities. While almost non-emissive in neutral solutions, treatment with acids or bases like trifluoroacetic acid (TFA) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) reveals distinct luminescence at wavelengths of 540 nm or 630 nm in propan-2-ol, respectively. Turn-ON emission can be detected at pH values as mild as pH = 5.31 or 8.70. Quantum yields in propan-2-ol are substantial for protonated (Φf = 0.058) and deprotonated (Φf = 0.059) species. Photometrically, pKa1 of 3.5 and pKa2 of 10.5 were determined in propan-2-ol. With lipophilic polyether sidechains and hydrophilic protonation and deprotonation sites the molecule can be regarded as amphipolar, which results in good solubility properties for different organic solvents. In aqueous media, an organic co-solvent like propan-2-ol (35%) or tetrahydrofuran (25%) is needed, and the solution can be diluted with pure water without precipitation of the compound. At higher concentrations of water, a turbid solution is formed, which indicates the formation of micellar structures or clusters. With dynamic light scattering we could show that these clusters increase in size with increasing water content.