Search

The functional properties of mammalian presynaptic nerve endings remain elusive since most terminals of the central nervous system are not accessible to direct electrophysiological recordings. In this study, direct recordings were performed for the first time at endbulb of Held terminals to characterize passive membrane properties, voltage-gated Ca(2+) channels (VGCCs) and Ca(2+)-dependent exocytosis. Endbulb of Held terminals arise from endings of auditory nerve fibres contacting spherical bushy cells (SBCs) in the anterior ventral cochlear nucleus (AVCN). These terminals had a high mean input resistance (1.1 G) and a small mean capacitance (4.3 pF). Presynaptic VGCCs were predominantly of the P/Q type (86%) and expressed at a high density with an estimated average number of 6400 channels per terminal. Presynaptic Ca(2+) currents (I(Ca(V))) activated and deactivated rapidly. Simulations of action potential (AP)-driven gating of VGCCs suggests that endbulb APs trigger brief Ca(2+) influx with a mean half-width of 240 μs and a peak amplitude of 0.45 nA which results from the opening of approximately 2600 channels. Unlike Ca(2+) currents at the calyx of Held, I(Ca(V)) of endbulb terminals showed no inactivation during trains of AP-like presynaptic depolarizations. Endbulb terminals are endowed with a large readily releasable vesicle pool (1064 vesicles) of which only a small fraction (10%) is consumed during a single AP-like stimulus. Fast presynaptic APs together with rapidly gating VGCCs will generate brief intracellular Ca(2+) transients that favour highly synchronous transmitter release. Collectively these characteristics ensure sustained and precise transmission of timing information from auditory stimuli at the endbulbSBC synapse.

The reorganization energy (lambda), which quantifies the structural rearrangement of a molecule when accommodating a charge, is a key parameter in the evaluation of charge mobility in molecular solids. However, it is unclear how lambda is influenced by conformational isomerism, which is diverse in amorphous solids. Here, we examine the conformational space of a family of model amorphous organic hole transport materials (HTMs), derived from triphenylamine in a core-arm template, and probe the effect of conformational complexity on lambda. We observe an extreme dependence of lambda on the conformer geometry of sterically congested HTMs, which to the best of our knowledge has not been described previously. These results serve as a cautionary tale that, while extracting the reorganization energy from a single molecular conformer optimized in the gas phase may be appropriate for rigid and sterically unencumbered structures, this approach is not suitable for many state-of-the-art HTMs that contain multiple bulky substituents.

Four spirobisacridine (SBA) hole-transporting materials were synthesized and employed in perovskite solar cells (PSCs). The molecules bear electronically inert alkyl chains of different length and bulkiness, attached to in-plane N atoms of nearly orthogonal spiro-connected acridines. Di-p-methoxyphenylamine (DMPA) substituents tailored to the central SBA-platform define electronic properties of the materials mimicking the structure of the benchmark 2,2',7,7'-tetrakis(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-MeOTAD), while the alkyl pending groups affect molecular packing in thin films and affect the long-term performance of PSCs. Devices with SBA-based hole transporting layers (HTL) attain efficiencies on par with spiro-MeOTAD. More importantly, solar cells with the new HTMs are hysteresis-free and demonstrate good operational stability, despite being doped as spiro-MeOTAD. The best performing MeSBA-DMPA retained 88% of the initial efficiency after a 1000 h aging test under constant illumination. The results clearly demonstrate that SBA-based compounds are potent candidates for a design of new HTMs for PSCs with improved longevity.

We present a fragment-based decomposition analysis tool (FB-REDA) for the reorganisation energy (lambda). This tool delivers insights on how to rationally design low-lambda organic semiconductors. The contribution of the fragment vibrational modes to the reorganization energy is exploited to identity the individual contributions of the molecular building blocks. The usefulness of the approach is demonstrated by offering three strategies to reduce the reorganization energy of a promising dopant-free hole transport material (TPA1PM, lambda = 213 meV). A reduction of nearly 50% (TPD3PM, lambda = 108 meV) is achieved. The proposed design principles are likely transferable to other organic semiconductors exploiting common molecular building blocks.

We explore several potential dopant-free triphenylamine-based hole transport materials for perovskite solar cells by combining two design strategies: (1) incorporation of multiple arms for mobility enhancement and (2) including Lewis bases that assist in defect passivation. Through multiscale computations along with the analysis of the electronic structure, molecular transport network, and data clustering, we established the relationship among hole mobility, transport parameters, intrinsic molecular properties, and molecular packing. Our results showed that multiarm design can be an effective strategy for 4-fold hole mobility enhancement (from 7 x 10(-6) to 3 x 10(-5) cm(2) V-1 s(-1)) through reducing the reorganization energy and energetic disorder. Furthermore, ionization potential (IP) optimization by changing substituents was performed because the IP decreases with an increasing number of arms. Via an adequate choice of substituents, the IP approaches the minus valence band maximum of MAPbI(3) and the hole mobility is further increased similar to 3-fold. The simulated mobility is in fair agreement with that obtained from field-effect transistors, supporting our computational protocols.

We present a fragment-based decomposition analysis tool (FB-ECDA) for the electronic coupling of charge transfer processes. This tool provides insight on the sophisticated relationship between molecular packing, electronic coupling, and the molecular transport network present in organic amorphous semiconductors. On the basis of atomic orbitals, FB-ECDA decomposes the total electronic coupling into individual electronic coupling terms arising from each molecular building blocks in a straightforward manner. The usefulness of this approach is demonstrated by revealing the structure-packing-property relationships for two series of molecules differing by the number of arm substituents and acene core length. Overall, we provide insight on the design of organic semiconductors exhibiting efficient charge transport network through achieving a subtle balance between molecular packing and electronic structure. We expect FB-ECDA to be a valuable tool for understanding sophisticated charge transfer processes in amorphous systems and guiding the rational design of organic semiconductors.