Organic solar cells (OSCs) have been a rising star in the field of renewable energy since the introduction of the bulk heterojunction (BHJ) in 1992. Recent advances have pushed the efficiencies of OSCs to over 13%, an impressive accomplishment via collaborative efforts in rational materials design and synthesis, careful device engineering, and fundamental understanding of device physics. Throughout these endeavors, several design principles for the conjugated donor polymers used in such solar cells have emerged, including optimizing the conjugated backbone with judicious selection of building blocks, side-chain engineering, and substituents. Among all of the substituents, fluorine is probably the most popular one; improved device characteristics with fluorination have frequently been reported for a wide range of conjugated polymers, in particular, donor-acceptor (D-A)-type polymers. Herein we examine the effect of fluorination on the device performance of solar cells as a function of the position of fluorination (on the acceptor unit or on the donor unit), aiming to outline a clear understanding of the benefits of this curious substituent. As fluorination of the acceptor unit is the most adopted strategy for D-A polymers, we first discuss the effect of fluorination of the acceptor units, highlighting the five most widely utilized acceptor units. While improved device efficiency has been widely observed with fluorinated acceptor units, the underlying reasons vary from case to case and highly depend on the chemical structure of the polymer. Second, the effect of fluorination of the donor unit is addressed. Here we focus on four donor units that have been most studied with fluorination. While device-performance-enhancing effects by fluorination of the donor units have also been observed, it is less clear that fluorine will always benefit the efficiency of the OSC, as there are several cases where the efficiency drops, in particular with "over-fluorination", i.e., when too many fluorine substituents are incorporated. Finally, while this Account focuses on studies in which the polymer is paired with fullerene derivatives as the electron accepting materials, non-fullerene acceptors (NFAs) are quickly becoming key players in the field of OSCs. The effect of fluorination of the polymers on the device performance may be different when NFAs are used as the electron-accepting materials, which remains to be investigated. However, the design of fluorinated polymers may provide guidelines for the design of more efficient NFAs. Indeed, the current highest-performing OSC (∼13%) features fluorination on both the donor polymer and the non-fullerene acceptor.

Solvent-free reversible deactivation radical polymerization of myrcene, a naturally occurring terpenoid monomer, with high regioselectivity was developed recently. Here, this green polymerization system is further improved to reach increased yields and produce polymers with high molar mass but still low dispersity and regioregular microstructure. To this end, two initiators (dibenzoyl peroxide, DBPO; azobis­(isobutyro­nitrile), AIBN) at 65, 90, and 130 °C were applied, and it was demonstrated that these varying conditions have a huge effect not only on the monomer conversion and the molar mass of the product, but also on the microstructure of the resulting polymyrcene. The polymerizations utilized two trithio­carbonate chain-transfer agents, and were similar in yields, molar masses, and dispersity of the produced polymyrcene, but progressed differently for the diverse initiator–temperature pairs. Generally, in all systems, pseudo-first-order kinetics, linear increase of molar mass with conversion, and low Đ values were found as a result of controlled polymerization. The systems using AIBN and DBPO initiators at 90 and 130 °C, respectively, have rate constants of propagation (k p app) lower than the decomposition rates (k d) of initiators, likewise important to control the polymerizations. At 130 °C, also branching occurred at the higher stage of the reaction, and lower regioregularity developed during the polymerization as a consequence of the favorable junction formation at elevated temperature and increased viscosity. Generally, compared to the previous study on the reversible deactivation radical polymerization of myrcene via reversible addition–fragmentation chain-transfer polymerization process, significantly higher conversions (30 → 65%) and increased chain length (9 → 40 kDa) were reached. The dispersity values for these polymerizations remained as low as 1.3–1.6, and also regioregular microstructures (up to 94%) were detected.

The complexation of Cm(III) with human serum transferrin was investigated in a pH range from 3.5 to 11.0 using time-resolved laser fluorescence spectroscopy (TRLFS). At pH ≥ 7.4 Cm(III) is incorporated at the Fe(III) binding site of transferrin whereas at lower pH a partially bound Cm(III) transferrin species is formed. At physiological temperature (310 K) at pH 7.4, about 70% of the partially bound and 30% of the incorporated Cm(III) transferrin species are present in solution. The Cm(III) results obtained by TRLFS are in very good agreement with Am(III) EXAFS results, confirming the incorporation of Am(III) at the Fe(III) binding site at pH 8.5.

Non-fullerene acceptors (NFAs) are becoming a serious contender to fullerene-based electron acceptors in organic photovoltaics, due to their structural versatility and easily tunable optical and electronic properties.