Thionated naphthalene diimides (NDIs) are promising materials for n-type organic semiconductors; despite their potential, synthetic routes to thionated NDIs are generally lengthy, nonselective, and low yielding and their polymeric analogues have yet to be reported in the literature. Here, we describe the rapid and selective thionation of thiophene- and selenophene-flanked NDIs using microwave irradiation and excess Lawesson's reagent. Remarkably, >99% conversion to the trans-dithionated product is observed by NMR within 45 min. Steric effects imparted by NDI core substituents prevent excess thionation, simplifying purification procedures. We apply this methodology to the postpolymerization thionation of NDI-based polymers to afford a series of polymers with varying degrees of thionation. Thionated NDIs exhibit bathochromic shifts of up to ∼100 nm in localized absorption maxima and increased electron affinities.

A series of donor−acceptor (D−A) and donor−acceptor−donor (D−A−D) molecules containing anthracene chromophores paired with a sulfur-containing acceptor group have been prepared. The oxidation state of the acceptor sulfur atom controls the degree of charge transfer character in the excited state wave function. Steady-state photoluminescence spectroscopy shows more pronounced solvatochromism with increasing sulfur oxidation state. Computational methods (DFT/TD-DFT) are used to show that orbital mixing between donor and acceptor is facilitated as the oxidation state of the acceptor sulfur is increased. ■ INTRODUCTIONThe formation of charge transfer (CT) or charge separated states in organic materials is central to the function of both organic photovoltaics (OPVs) 1−3 and light-emitting diodes (OLEDs). 4 In OPVs, the binding energy of an electron/hole pair (Frenkel exciton) determines the ability to separate charges. In OLEDs, electrons and holes are injected from opposite electrodes and combine in the emitting layer of these devices to form luminescent (Frenkel) excitons. 5 At separations greater than the capture radius (typically >100 Å), the polarons have uncorrelated spin states. However, upon capture, an initially formed CT state results which possesses either singlet ( 1 CT) or triplet ( 3 CT) character. In most systems the 1 CT and 3 CT excitons decay to their respective Frenkel excitons in a 1:3 singlet/triplet statistical distribution. With fluorescent materials this statistical branching ratio results in an upper limit for electroluminescence efficiency of 25% as triplet excitons typically decay nonradiatively without the presence of strong spin−orbit coupling. 6 Recently, two separate mechanisms, (1) thermally activated delayed fluorescence (TADF) 7 and (2) "extra-fluorescence", 8 have been proposed for deliberately controlling the singlet/ triplet branching ratio in an electroluminescent device. In the case of TADF it has been demonstrated that by introducing charge transfer in the excited state, the singlet/triplet energy gap (ΔE ST ) can be reduced. By reducing ΔE ST , triplet excitons can be thermally promoted to the emissive singlet state, enabling >25% internal quantum efficiency. Extra-fluorescence, much like TADF, is a photophysical process by which >25% singlet exciton formation is achieved by controlling the decay of singlet and triplet charge transfer states ( 1 CT/ 3 CT) to their respective singlet and triplet Frenkel excitons. For instance, if the energy difference between 1 CT and 3 CT is small, then the rate of singlet (k s ) and triplet (k t ) formation (from 1 CT and 3 CT states) will control the singlet exciton fraction. For both of these methods, deliberate engineering of CT states in the emitting molecules is used to control the singlet/triplet exciton ratio. Accordingly, methods to deliberately interrogate the effect of CT in organic chromophores are of interest.Control over CT states is also expected to be important in singlet fission, a photophysical process by which an excited singl...

Organic electrodes are promising candidates for nextgeneration lithium-ion batteries due to their low cost and sustainable nature; however, they often suffer from very low conductivity and active material loadings. The conventional binder used in organic-based Li-ion batteries is poly(vinylidene fluoride) (PVDF), yet it is electrochemically inactive and thus occupies volume and mass without storing energy. Here, we report an organic mixed ionic-electronic conducting polymer, polyPEDOT-b-PEG for simplicity, as a cathode binder to address the aforementioned issues. The polymer contains a poly(3,4-ethylenedioxythiophene) (PEDOT) functionality to provide electronic conductivity, as well as poly(ethylene glycol) (PEG) chains to impart ionic conductivity to the cathode composite. We compare electrodes containing a perylene diimide (PDI) active material, conductive carbon, and a polymeric binder (either PVDF or PEDOT-b-PEG) with different weight ratios to study the impact of active material loading and type of binder on the performance of the cell. The lithium-ion cells prepared with the PEDOT-b-PEG polymer binder result in higher capacities and decreased impedance at all active material loadings compared to cathodes prepared with the PVDF-containing electrodes, demonstrating potential as a new binder to achieve higher active material loadings in organic electrodes. The strategy of preparing these polymers should be broadly applicable to other classes of mixed polymer conductors.

Templated oxidative polymerization affords organic soluble, oxidatively doped PEDOT-based polymers with controlled molecular weights and low dispersities (Đ ∼ 1.2) for the first time.

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