Evidence of polarized charge-transfer transitions by probing the weak dielectric tensor components of oligothiophene crystals

Unbound exciton–phonon states in oligothiophene crystals – A model approach for spectroscopic purposes

“…2 along with the corresponding experimental spectrum [21]. The position of the lower Davydov component (defining the zero of energy in the plot), as well as the total intensity, are taken for granted and are adjusted to fit the experimental spectrum.…”

“…The width 2C of the exciton band is identified with the Davydov splitting at k = 0. Its calculated value of 1 eV [22] is fine-tuned to 1.083 eV in order to fit exactly the experimental position of the upper Davydov component [21,23]. When expressed in the units of leading progression-forming mode, this yields C = 3.012.…”

Optical Properties of Molecular Crystals: The Effect of Molecular Packing and Polymorphism

“…The maximum intensity is detected for the highest positive angle of incidence (the centre of the band can be tentatively deduced to be 3.75 eV), it decreases with decreasing angle of incidence down to zero at about -15°, and finally it again emerges slightly shifted at higher energy (the maximum is found at about 3.85 eV). This indicates that the corresponding transition moment has a strong component along the normal to the surface and shows directional dispersion (Philpott 1969;Spearman et al 2005;Tavazzi et al 2006b;Weiser & Moller 2002). Considering that the band disappears at about -15°, the inclination of the transition moment to the normal to the surface can be approximately estimated from the experiment to be of the order of -10° (taking into consideration the effect of refraction at the air/crystal interface).…”

“…First we compute the microscopic mechanical exciton states and then we consider the propagation of light in an anisotropic medium, including long-range interactions through the macroscopic dielectric tensor. This theoretical approach takes full account of all the crystal symmetries and the numerical calculations provide a fairly accurate description of the dispersion of the purely excitonic bands, allowing a quantitative comparison with experiments (Raimondo et al 2006;Silvestri et al 2009;Spearman et al 2005;Tavazzi et al 2006aTavazzi et al , 2006b.…”

“…where k inc is the wave vector of the incoming light (|k inc |~0) and d is the excitonic dipole moment (Philpott 1969;Spearman et al 2005;Tavazzi et al 2006b;Weiser & Moller 2002). Thus, TPP is an example with strong directional dispersion (energy and shape of the absorption band are strongly dependent on the angle of incidence on the crystal face).…”