Building efficient triplet-harvesting layers for photovoltaic applications requires a deep understanding of the microscopic properties of the components involved and their dynamics. Singlet fission is a particularly appealing mechanism as it generates two excitons from a single photon. However, the pathways of the coupled triplets into free species, and their dependence on the intermolecular geometry, has not been fully explored. In this work, we produce highly ordered dilute pentacene films with distinct parallel and herringbone dimers and aggregates. Using electron paramagnetic resonance spectroscopy, we provide compelling evidence for the formation of distinct quintet excitons in ambient conditions, with intrinsically distinctive electronic and kinetic properties. We find that the ability of quintets to separate into free triplets is promoted in the parallel dimers and this provides molecular design rules to control the triplets, favouring either enhanced photovoltaic efficiency (parallel) or strongly bound pairs that could be exploited for logic applications (herringbone).

Moving from hexagonal boron nitride (h-BN), a well-known crystalline insulator, to amorphous BN, leads to the creation of a semiconductor able to photoreduce CO2 in the gas/solid phase, under UV-vis and pure visible light.

Porous boron nitride (BN), a combination of hexagonal, turbostratic and amorphous BN, has emerged as a new platform photocatalyst. Yet, this material lacks photoactivity under visible light. Theoretical studies predict that tuning the oxygen content in oxygen-doped BN (BNO) could lower the band gap. This is yet to be verified experimentally. We present herein a systematic experimental route to simultaneously tune BNO's chemical, magnetic and optoelectronic properties using a multivariate synthesis parameter space. We report deep visible range band gaps (1.50-2.90 eV) and tuning of the oxygen (2-14 at.%) and specific paramagnetic OB 3 contents (7-294 a.u. g À 1 ). Through designing a response surface via a design of experiments (DOE) process, we have identified synthesis parameters influencing BNO's chemical, magnetic and optoelectronic properties. We also present model prediction equations relating these properties to the synthesis parameter space that we have validated experimentally. This methodology can help tailor and optimise BN materials for heterogeneous photocatalysis.

A combination of inelastic neutron scattering (INS), far-IR magnetospectroscopy (FIRMS), and Raman magneto-spectroscopy (RaMS) has been used to comprehensively probe magnetic excitations in Co(AsPh 3 ) 2 I 2 (1), a reported singlemolecule magnet (SMM). With applied field, the magnetic zero-field splitting (ZFS) peak (2D′) shifts to higher energies in each spectroscopy. INS placed the ZFS peak at 54 cm −1 , as revealed by both variable-temperature (VT) and variable-magnetic-field data, giving results that agree well with those from both far-IR and Raman studies. Both FIRMS and RaMS also reveal the presence of multiple spin−phonon couplings as avoided crossings with neighboring phonons. Here, phonons refer to both intramolecular and lattice vibrations. The results constitute a rare case in which the spin− phonon couplings are observed with both Raman-active (g modes) and far-IR-active phonons (u modes; space group P2 1 /c, no. 14, Z = 4 for 1). These couplings are fit using a simple avoided crossing model with coupling constants of ca. 1−2 cm −1 . The combined spectroscopies accurately determine the magnetic excited level and the interaction of the magnetic excitation with phonon modes. Density functional theory (DFT) phonon calculations compare well with INS, allowing for the assignment of the modes and their symmetries. Electronic calculations elucidate the nature of ZFS in the complex. Features of different techniques to determine ZFS and other spin-Hamiltonian parameters in transition-metal complexes are summarized.

This work investigates the evolution of structure and morphology of pure and co-evaporated thin films, as a function of pentacene concentration in a solid host of p-terphenyl.

Effective control over the molecular orientation of pentacene was achieved with copper(i) iodide and results in a change in the functional properties with increases in both visible light absorption and work function.

<p>Developing robust, multifunctional photocatalysts that can facilitate both hydrogen evolution via photoreforming of water and gas phase CO2 photoreduction is highly desirable with the long-term vision of integrated photocatalytic setups. Here, we present a new addition to the boron nitride (BN) photocatalyst material platform, boron-doped boron oxynitride (B-BNO), capable of fulfilling this goal. Detailed EPR studies revealed hyperfine interactions between free charges located on discrete OB3 sites, exhibiting an out-of-plane symmetry, and the nuclei of neighbouring boron atoms. This material resolves two long-standing bottlenecks associated to BN-based materials concomitantly: instability in water and lack of photo activity under visible light. We show that B-BNO maintains prolonged stability in water for at least three straight days and can facilitate both liquid phase H2 evolution and gas phase CO2 photoreduction, using UV-Vis and deep visible irradiation (λ > 550 nm), without any cocatalysts. The evolution rates, apparent quantum yields, and selectivities observed for both reactions with B-BNO exceed those of its porous BNO counterpart, P25 TiO2 and bulk g-C3N4. This work provides scope to expand the BN photocatalyst platform to a wider range of reactions.</p>

Singlet fission -whereby one absorbed photon generates two coupled triplet excitons -is a key process for increasing the efficiency of optoelectronic devices by overcoming the Shockley-Queisser limit. A crucial parameter is the rate of dissociation of the coupled triplets, as this limits the number of free triplets subsequently available for harvesting and ultimately the overall efficiency of the device. Here, we present an analysis of the thermodynamic and kinetic parameters for this process in parallel and herringbone dimers measured by electron paramagnetic resonance spectroscopy in co-evaporated films of pentacene in p-terphenyl. The rate of dissociation is faster for parallel dimers than for their herringbone counterparts, as is the recombination to the ground state. DFT calculations, which provide the magnitude of the electronic coupling as well as the distribution of molecular orbitals for each geometry, suggest that lower triplet coupling in the parallel dimer is the driving force for faster dissociation. Conversely, localization of the molecular orbitals and stronger triplet-triplet interaction result in slower dissociation and recombination. The identification and understanding of how intermolecular geometry promote efficient triplet dissociation provides the basis for control of triplet coupling and thereby the optimization of one important parameter of device performance.