Current approaches to synthesize π‐conjugated polymers (CPs) are dominated by thermally driven, transition‐metal‐mediated reactions. Herein we show that electron‐deficient Grignard monomers readily polymerize under visible‐light irradiation at room temperature in the absence of a catalyst. The product distribution can be tuned by the wavelength of irradiation based on the absorption of the polymer. Conversion studies are consistent with an uncontrolled chain‐growth process; correspondingly, chain extension produces all‐conjugated n‐type block copolymers. Preliminary results demonstrate that the polymerization can be expanded to donor–acceptor alternating copolymers. We anticipate that this method can serve as a platform to access new architectures of n‐type CPs without the need for transition‐metal catalysis.

The functional integration of atomically defined graphene nanoribbons (GNRs) into single-ribbon electronic device architectures has been limited by access to nondestructive high-resolution imaging techniques that are both compatible with common supports such as Si or Si/SiO wafers and capable of resolving individual ribbons in dilute samples. Conventional techniques such as scanning probe (AFM, STM) or electron microscopy (SEM, TEM) have been restricted by requisite sample preparation techniques that are incompatible with lithographic device fabrication. Here we report the design and synthesis of ultralong (∼10 μm) cove-type GNRs (cGNRs) featuring azide groups along the edges that can serve as a universal handle for late-stage functionalization with terminal alkynes. Copper-catalyzed click-chemistry with Cy5 fluorescent dyes gives rise to cGNRs decorated along the edges with fluorescent tags detectable by optical microscopy. The structures of individual dye-functionalized cGNRs spin-coated from a dilute solution onto transparent and opaque insulating substrates were resolved using diffraction-limited fluorescence microscopy and super-resolution microscopy (SRM) imaging techniques. Analysis of SRM images reveals an apparent width of cGNRs in the range 40-50 nm and lengths in excess of 10 μm, the longest GNRs imaged to date. Isolated cGNRs can even be distinguished from bundles and larger aggregates as long as the center-to-center distance is greater than the apparent width.

π-Conjugated polymers (CPs) combine the flexibility, processability, and lightness of plastics with semiconducting properties for optoelectronic applications. These polymers are conventionally synthesized by thermal transition-metal-catalyzed polycondensation. Photochemical approaches to CPs offer the possibility of direct photopatterning, but present mechanistic challenges. Shimidzu first described the photopolymerization of thiophene derivatives in the 1990s, but the field lay dormant for many years. Recently, both oxidative and reductive photopolymerizations have been developed to access p-type and ntype materials. This Minireview summarizes these developments and the outlook for this nascent field.

π-Conjugated polymers can serve as active layers in flexible and lightweight electronics, and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein we describe an experimental and computational investigation into the mechanism of this photopolymerization. Spectroscopic studies performed in situ and after quenching reveal that the propagating chain is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated SRN1type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp 2 radicals and enables C-C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus favor productive monomer binding.

Current approaches to synthesize π-conjugated polymers are dominated by thermally driven, transition metal-mediated methods. Herein we show that electron-deficient Grignard monomers readily polymerize under visible light irradiation at room temperature in the absence of a catalyst. The product distribution can be tuned by the wavelength of irradiation based on the absorption of the polymer. Conversion studies are consistent with an uncontrolled chain-growth process; correspondingly, chain extension produces blocky all-conjugated copolymers. Preliminary results demonstrate that the polymerization can be expanded to donor-acceptor alternating copolymers. We anticipate that this method can serve as a platform to access new architectures of n-type conjugated polymers without the need for transition metal catalysis.