One of the most effective ways to tune the electronic properties of conjugated polymers is to dope them with small-molecule oxidizing agents, creating holes on the polymer and molecular anions. Undesirably, strong electrostatic attraction from the anions of most dopants localize the holes created on the polymer, reducing their mobility. Here, we employ a new strategy utilizing a substituted boron cluster as a molecular dopant for conjugated polymers. By designing the cluster to have a high redox potential and steric protection of the corelocalized electron density, we obtain highly delocalized polarons with mobilities equivalent to films doped with no anions present. AC Hall effect measurements show that P3HT films doped with our boron clusters have conductivities and polaron mobilities roughly an order of magnitude higher than films doped with F 4 TCNQ, even though the boron-cluster-doped films have poor crystallinity. Moreover, the number of free carriers approximately matches the number of boron clusters, yielding a doping efficiency of ∼100%. These results suggest that shielding the polaron from the anion is a critically important aspect for producing high carrier mobility, and that the high polymer crystallinity required with dopants such as F 4 TCNQ is primarily to keep the counterions far from the polymer backbone.

We recently reported the photophysical properties of boron dipyridylmethene (DIPYR) dyes, a class of intensely fluorescent pyridine-based chromophores, which are structural analogues of both acenes and BODIPYs. In this work, we endeavored to explore the properties of DIPYR dimers. The synthesis and characterization of two novel homoleptic meso-linked dimers of boron dipyridylmethene dyes, bis-DIPYR and bis-α-DIPYR, are herein reported. Their structural, electrochemical, and photophysical properties have been probed using both steady-state and time-resolved techniques including femtosecond and nanosecond transient absorption spectroscopies. Of particular focus are the excited-state photophysical dynamics of the dimers, which are studied in several solvents of varying polarity, from methylcyclohexane to acetonitrile. It was found that both dimers undergo symmetry-breaking charge transfer within 3 ps of photoexcitation, forming a radical anion and radical cation, which were observed using transient absorption and confirmed by spectroelectrochemical characterization. Further, it was found that the emitting species is the symmetry-broken state, which is stable for several nanoseconds before radiative recombination to the ground state occurs. The efficiency and rapidity of symmetry breaking, even in nonpolar media, is highly promising for application of these materials to optoelectronic technologies requiring charge transfer from an excitonic state.

The measurement of the dimerization constants of hydrogen-bonded ruthenium complexes (1 2, 2 2, 3 2) linked by a self-complementary pair of 4-pyridylcarboxylic acid ligands in different redox states is reported.

Electron transfer across a mixed-valent hydrogen-bonded self-dimer of oxo-centered triruthenium clusters bridged by a pair of 4(3H)-pyrimidinones is reported. Spectroelectrochemical studies in methylene chloride reveal that 1 rapidly self-dimerizes upon oneelectron reduction, forming the strongly coupled mixedvalent hydrogen-bonded dimer (1 2 ) − . In the mixed-valent state, significantly broadened, partially coalesced ν(CO) bands are observed, allowing estimation of the electron transfer rate (k ET ) by an optical Bloch line shape analysis. Simulation of the FTIR line shapes provides an estimate of k ET on the order of 10 11 s −1 , indicating a highly delocalized electronic structure across the hydrogen bonds. These findings are supported by the determination of the formation constant (K MV ) for (1 2 ) − , which is found to be on the order of 10 6 M −1 , or nearly 4 orders of magnitude higher than that for the neutral isovalent dimer (1 2 ). This represents a stabilization of approximately 5.7 kcal/mol (1980 cm −1 ) arising from electron exchange across the hydrogen bonds in the mixed-valent state. Significantly, an enormous intensity enhancement of the amide ν(NH) band (3300 cm −1 ) of (1 2 ) − is observed, supporting strong mixing of the bridging ligand vibrational modes with the electronic wave function of the mixedvalent state. These findings demonstrate strong donor− bridge−acceptor coupling and that highly delocalized electronic structures can be attained in hydrogen-bonded systems, which are often considered to be too weakly bound to support strong electronic communication.