1. This paper describes two novel population patterns in the dentate gyrus of the awake rat, termed type 1 and type 2 dentate spikes (DS1, DS2). Their cellular generation and spatial distribution were examined by simultaneous recording of field potentials and unit activity using multiple-site silicon probes and wire electrode arrays. 2. Dentate spikes were large amplitude (2-4 mV), short duration (< 30 ms) field potentials that occurred sparsely during behavioral immobility and slow-wave sleep. Current-source density analysis revealed large sinks in the outer (DS1) and middle (DS2) thirds of the dentate molecular layer, respectively. DS1 and DS2 had similar longitudinal, lateral, and interhemispheric synchrony. 3. Dentate spikes invariably were coupled to synchronous population bursts of putative hilar interneurons. CA3 pyramidal cells, on the other hand were suppressed during dentate spikes. 4. After bilateral removal of the entorhinal cortex, dentate spikes disappeared, whereas sharp wave-associated bursts, reflecting synchronous discharge of the CA3-CA1 network, increased several fold. 5. These physiological characteristics of the dentate spikes suggest that they are triggered by a population burst of layer II stellate cells of the lateral (DS1) and medial (DS2) entorhinal cortex. 6. We suggest that dentate spike-associated synchronized bursts of hilar-region interneurons provide a suppressive effect on the excitability of the CA3-CA1 network in the intact brain.

With rapid advances in material synthesis and device performance, the long‐term stability of organic solar cells has become the main remaining challenge toward commercialization. An investigation of photodegradation in blend films of the donor polymer poly(3‐hexylthiophene) (P3HT) and the rhodanine‐flanked small molecule acceptor 5,5′‐[(9,9‐dioctyl‐9H‐fluorene‐2,7‐diyl)bis(2,1,3‐benzothiadiazole‐7,4‐diylmethylidyne)]bis[3‐ethyl‐2‐thioxo‐4‐thiazolidinone] (FBR) is presented in an ambient atmosphere. The photobleaching kinetics of the pure materials and their blends is correlated with the generation of radicals and triplet excitons using optical and magnetic resonance techniques. In addition, spin‐trapping methods are employed to identify reactive oxygen species (ROS). In films of P3HT, FBR, and the P3HT:FBR blend, superoxide is generated by electron transfer to molecular oxygen. However, it is found that the generation of singlet oxygen by energy transfer from the FBR triplet state is responsible for the poor stability of FBR and for the accelerated photodegradation at later times of the P3HT:FBR blend. In the early stage of degradation of the neat blend, it is protected from singlet oxygen by the fast donor–acceptor charge transfer, which competes with triplet exciton formation. These results provide initial input for a rational design of donor and acceptor materials through tuning the molecular singlet and triplet energy levels to prevent ROS‐related photodegradation.

X-ray diffraction (XRD) and electron paramagnetic resonance spectroscopy (EPR) were combined to study the structural transformations induced by temperature, pressure and air humidity of the "breathing" metal-organic framework (MOF) MIL-53(Al), doped with paramagnetic V ions, after activation. The correlation between in situ XRD and thermogravimetric analysis measurements showed that upon heating this MOF in air, starting from ambient temperature and pressure, the narrow pore framework first dehydrates and after that makes the transition to a large pore state (lp). The EPR spectra of V[double bond, length as m-dash]O molecular ions, replacing Al-OH in the structure, also allow to distinguish the as synthesized, hydrated (np-h) and dehydrated narrow pore (np-d), and lp states of MIL-53(Al). A careful analysis of EPR spectra recorded at microwave frequencies between 9.5 and 275 GHz demonstrates that all V[double bond, length as m-dash]O in the np-d and lp states are equivalent, whereas in the np-h state (at least two) slightly different V[double bond, length as m-dash]O sites exist. Moreover, the lp MIL-53(Al) framework is accessible to oxygen, leading to a notable broadening of the V[double bond, length as m-dash]O EPR spectrum at pressures of a few mbar, while such effect is absent for the np-h and np-d states for pressures up to 1 bar.

2D hybrid perovskites consisting of layers of lead halide octahedra separated by long organic linker cations have great potential for functional material design toward tailored optical and electronic properties. Here, we report the first direct observation of light-induced charge transfer (CT) in a series of novel 2D perovskites incorporating conjugated linkers based on the carbazole molecule. Dedicated electron paramagnetic resonance experiments and supporting quantum-chemical calculations reveal that excitons generated in the lead halide layer undergo CT at the organic–inorganic interface, resulting in a positive polaron delocalized over several carbazole moieties and a partner electron residing in the inorganic layer. The occurrence of such CT processes in these materials not only offers interesting new perspectives for the functionalization of future 2D perovskites but could also lead to a better understanding of the unusual broadband emission reported for this material class, which has been directly related to polaronic effects.

Abstract3D hybrid perovskites (APbX3) have made a significant impact on the field of optoelectronic materials due to their excellent performance combined with facile solution deposition and up‐scalable device fabrication. Nonetheless, these materials suffer from environmental instability. To increase material stability, the organic cation (A) is substituted by the non‐volatile cesium cation. However, the desired photoactive cesium lead(II) iodide black phase is metastable in ambient conditions and spontaneously converts into the photo‐inactive yellow δ‐phase. In this work, the black phase is stabilized by the formation of a quasi‐2D perovskite containing a benzothieno[3,2‐b]benzothiophene (BTBT) large organic ammonium cation. Thermal analysis shows that degradation of the butylammonium (BA)‐based quasi‐2D perovskite (BA)2CsPb2I7 sets in at ≈130 °C, while (BTBT)2CsPb2I7 is phase‐stable until ≈230 °C. Additionally, the (BTBT)2CsPb2I7 film does not show any sign of degradation after exposure to 77% Relative Humidity in the dark for 152 days, while (BA)2CsPb2I7 degrades in a single day. Photoconductor‐type detectors based on (BTBT)2CsPb2I7 demonstrate an increased external quantum efficiency and a similar specific detectivity compared to the BA‐based reference detectors. The results demonstrate the utility of employing a BTBT cation within the organic layer of quasi‐2D perovskites to significantly enhance the stability while maintaining the optoelectronic performance.