Far infrared response of α- and αt-(BEDT-TTF)2I3

The temperature dependence of the reflectivity of α- and α t-(BEDT-TTF)2I3 was determined in the 10-700 cm-1 range. Moreover the transmission spectra of α-phase between 10 and 33 cm-1 were studied. Using Kramers-Kronig analysis the IR conductivity and permittivity were calculated. The similarity of α t and β-phases was confirmed. The spectra in the metallic phase are dominated by a broad electronic peak between 200 and 500 cm-1 which can be understood as due to transitions across the small gap whose origin is discussed. In the spectra a rich phonon peak structure is observed, mostly of vibronic origin. It is suggested that non totally symmetric modes of BEDT-TTF molecule can couple with electrons.On a déterminé la dépendance en température de la réflectivité des phases α et αt de (BEDT-TTF)2I3 dans le domaine 10-700 cm-1. En outre, on a étudié les spectres de transmission de la phase α entre 10 et 33 cm-1. La conductivité infrarouge et la permittivité ont été calculées au moyen d'une analyse Kramers-Kronig. Des similarités ont été notées entre les phases αt et β. Des transitions à travers un petit gap (dont l'origine reste à discuter) permettent d'interpréter le pic élargi de la phase métallique situé entre 200 et 500 cm-1. Une structure foisonnante en pics est attribuée à des effets vibroniques. Nous suggérons que des modes impartiellement symétriques de la molécule BEDT-TTF peuvent être couplés aux électrons

Redox chemistry in the pigment eumelanin as a function of temperature using broadband dielectric spectroscopy

Conductive biomolecular systems are investigated for their promise of new technologies. One biomolecular material that has garnered interest for device applications is eumelanin. Its unusual properties have led to its incorporation in a wide set of platforms including transistor devices and batteries. Much of eumelanin's conductive properties are due to a solid state redox comproportionation reaction. However, most of the work that has been done to demonstrate the role of the redox chemistry in eumelanin has been via control of eumelanin's hydration content with scant attention given to temperature dependent behavior. Here we demonstrate for the first time consistency between hydration and temperature effects for the comproportionation conductivity model utilizing dielectric spectroscopy, heat capacity measurements, frequency scaling phenomena and recognizing that activation energies in the range of ∼0.5 eV correspond to proton dissociation events. Our results demonstrate that biomolecular conductivity models should account for temperature and hydration effects coherently