N-Heteroacenes as an Organic Gain Medium for Room-Temperature Masers

The development of future quantum devices such as the maser, i.e., the microwave analog of the laser, could be well-served by the exploration of chemically tunable organic materials. Current iterations of room-temperature organic solid-state masers are composed of an inert host material that is doped with a spin-active molecule. In this work, we systematically modulated the structure of three nitrogen-substituted tetracene derivatives to augment their photoexcited spin dynamics and then evaluated their potential as novel maser gain media by optical, computational, and electronic paramagnetic resonance (EPR) spectroscopy. To facilitate these investigations, we adopted an organic glass former, 1,3,5-tri(1-naphthyl)benzene to act as a universal host. These chemical modifications impacted the rates of intersystem crossing, triplet spin polarization, triplet decay, and spin–lattice relaxation, leading to significant consequences on the conditions required to surpass the maser threshold

Quantum transport through STM-lifted single PTCDA molecules

Using a scanning tunneling microscope we have measured the quantum conductance through a PTCDA molecule for different configurations of the tip-molecule-surface junction. A peculiar conductance resonance arises at the Fermi level for certain tip to surface distances. We have relaxed the molecular junction coordinates and calculated transport by means of the Landauer/Keldysh approach. The zero bias transmission calculated for fixed tip positions in lateral dimensions but different tip substrate distances show a clear shift and sharpening of the molecular chemisorption level on increasing the STM-surface distance, in agreement with experiment.Comment: accepted for publication in Applied Physics

Analysis of Bonding between Conjugated Organic Molecules and Noble Metal Surfaces Using Orbital Overlap Populations

The electronic structure of metal−organic interfaces is of paramount importance for the properties of organic electronic and single-molecule devices. Here, we use so-called orbital overlap populations derived from slab-type band-structure calculations to analyze the covalent contribution to the bonding between an adsorbate layer and a metal. Using two prototypical molecules, the strong acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) on Ag(111) and the strong donor 1H,1′H-[4,4′]bipyridinylidene (HV0) on Au(111), we present overlap populations as particularly versatile tools for describing the metal−organic interaction. Going beyond traditional approaches, in which overlap populations are represented in an atomic orbital basis, we also explore the use of a molecular orbital basis to gain significant additional insight. On the basis of the derived quantities, it is possible to identify the parts of the molecules responsible for the bonding and to analyze which of the molecular orbitals and metal bands most strongly contribute to the interaction and where on the energy scale they interact in bonding or antibonding fashion

N-heteroacenes as an organic gain medium for room temperature masers

The development of future quantum devices such as the maser, i.e., the microwave analog the laser, could be well-served by exploration of chemically tuneable organic materials. Current iterations of room temperature organic solid-state masers are composed of an inert host material that is doped with a spin-active molecule. In this work, we have systematically modulated the structure of three nitrogen-substituted tetracene derivatives to augment their photoexcited spin dynamics and then evaluated their potential as novel maser gain media. To facilitate these investigations, we adopted an organic glass former, 1,3,5-tri(1-naphthyl)benzene (1-TNB) to act a universal host. These chemical modifications impacted the rates of intersystem crossing, triplet spin polarisation, triplet decay and spin-lattice relaxation, leading to significant consequences on the conditions required to surpass the maser threshold

Homelessness and the refugee: De-valorizing displacement in Abdulrazak Gurnah’s By the Sea

© 2015 Taylor & Francis The use of postmodern discourses of movement to analyze literary works involving migration has contributed to a valorization of displacement, which tends to be seen as both inherently resistant and creatively productive. While such approaches have been important for problematizing hegemonic mobilizations of “home”, there is also a danger in reading movement as constitutive of the (post)modern world. In particular, such frameworks often overlook the experiences of those who are forcibly displaced. Critical investment in tropes of migrancy may unwittingly recycle imperialist assumptions by producing imagined spaces of alterity that serve to liberate the centred, “at home” subject at the expense of historicized experiences of homelessness. Abdulrazak Gurnah’s 2001 novel By the Sea represents one such historicized experience, that of its protagonist, asylum seeker Saleh Omar. This article argues that, through its narrative investment in houses and household objects and in the importance of narrative for creating a sense of home for its migrant protagonist, Gurnah’s novel poses a challenge to an aesthetic valorization of displacement. Furthermore, rather than identifying an individualist investment in homelessness as a route to authorship, By the Sea posits storytelling rooted in the domestic sphere as an alternative, restorative migrant aesthetic practice