Perpendicular crossing chains enable high mobility in a noncrystalline conjugated polymer.

The nature of interchain π-system contacts, and their relationship to hole transport, are elucidated for the high-mobility, noncrystalline conjugated polymer C16-IDTBT by the application of scanning tunneling microscopy, molecular dynamics, and quantum chemical calculations. The microstructure is shown to favor an unusual packing motif in which paired chains cross-over one another at near-perpendicular angles. By linking to mesoscale microstructural features, revealed by coarse-grained molecular dynamics and previous studies, and performing simulations of charge transport, it is demonstrated that the high mobility of C16-IDTBT can be explained by the promotion of a highly interconnected transport network, stemming from the adoption of perpendicular contacts at the nanoscale, in combination with fast intrachain transport.

Element-specific investigations of ultrafast dynamics in photoexcited CuZnSnS nanoparticles in solution.

Ultrafast, light-induced dynamics in copper-zinc-tin-sulfide (CZTS) photovoltaic nanoparticles are investigated through a combination of optical and x-ray transient absorption spectroscopy. Laser-pump, x-ray-probe spectroscopy on a colloidal CZTS nanoparticle ink yields element-specificity, which reveals a rapid photo-induced shift of electron density away from Cu-sites, affecting the molecular orbital occupation and structure of CZTS. We observe the formation of a stable charge-separated and thermally excited structure, which persists for nanoseconds and involves an increased charge density at the Zn sites.

Simulation of time-resolved x-ray absorption spectroscopy of ultrafast dynamics in particle-hole-excited 4-(2-thienyl)-2,1,3-benzothiadiazole.

To date, alternating co-polymers based on electron-rich and electron-poor units are the most attractive materials to control functionality of organic semiconductor layers in which ultrafast excited-state processes play a key role. We present a computational study of the photoinduced excited-state dynamics of the 4-(2-thienyl)-2,1,3-benzothiadiazole (BT-1T) molecule, which is a common building block in the backbone of -conjugated polymers used for organic electronics. In contrast to homo-polymer materials, such as oligothiophene, BT-1T has two non-identical units, namely, thiophene and benzothiadiazole, making it attractive for intramolecular charge transfer studies.

Benchmarking triplet-triplet annihilation photon upconversion schemes.

Photon upconversion facilitated by triplet-triplet annihilation in molecular systems is a promising path toward utilization of sub bandgap photons in photovoltaic devices. Prior to the challenging synthesis of new molecules, quantum chemical computations can aid the design process and provide suggestions for new and optimal systems. Here, we benchmark time-dependent density functional methods by their ability to describe relevant photophysical quantities of a range of different types of sensitizer/annihilator pairs to provide guidelines for future computational studies of potential new pairs.

Molecular solar thermal systems - control of light harvesting and energy storage by protonation/deprotonation.

Molecular solar thermal (MOST) systems that undergo photoisomerizations to long-lived, high-energy forms present one approach of addressing the challenge of solar energy storage. For this approach to mature, photochromic molecules which can absorb at the right wavelengths and which can store a sufficient amount of energy in a controlled time period have to be developed. Here we show in a combined experimental and theoretical study that incorporation of a pyridyl substituent onto the dihydroazulene/vinylheptafulvene photo-/thermoswitch results in molecules whose optical properties, energy-releasing back-reactions and energy densities can be controlled by protonation/deprotonation.

Density Functional Theory Study of the Solvent Effects on Systematically Substituted Dihydroazulene/Vinylheptafulvene Systems: Improving the Capability of Molecular Energy Storage.

Former work has improved the energy storage capacity of the dihydroazulene/vinylheptafulvene photo/thermoswitch by substitution with NH and NO in vacuum. This work extends the former by investigating the solvent effects systematically using cyclohexane, toluene, dichloromethane, ethanol, and acetonitrile and comparing them with the inclusion of vacuum calculations. The investigation includes more than 8000 calculations using density functional theory for comparison of energy storage capacities, activation energies for the thermal conversion of vinylheptafulvene to dihydroazulene, and UV-Vis absorption spectra.

Aromaticity-Controlled Energy Storage Capacity of the Dihydroazulene-Vinylheptafulvene Photochromic System.

Photochemical conversion of molecules into high-energy isomers that, after a stimulus, return to the original isomer presents a closed-cycle of light-harvesting, energy storage, and release. One challenge is to achieve a sufficiently high energy storage capacity. Here, we present efforts to tune the dihydroazulene/vinylheptafulvene (DHA/VHF) couple through loss/gain of aromaticity.

Characterisation of dihydroazulene and vinylheptafulvene derivatives using Raman spectroscopy: The CN-stretching region.

The effect of adding electron donating and withdrawing groups on the dihydroazulene (DHA)/vinylheptafulvene (VHF) photochromic system has been investigated using Raman spectroscopy in CS2 solutions. The photoswitching between DHA and VHF is often characterised with UV-Vis spectroscopy. However, Raman spectroscopy can also be used for this purpose and give structural insight, as the light induced ring-opening from DHA to VHF causes changes in the CN-stretching frequencies.