Diradicals acting through diamagnetic phenylene vinylene bridges: Raman spectroscopy as a probe to characterize spin delocalization.

We present a complete Raman spectroscopic study in two structurally well-defined diradical species of different lengths incorporating oligo p-phenylene vinylene bridges between two polychlorinated triphenylmethyl radical units, a disposition that allows sizeable conjugation between the two radicals through and with the bridge. The spectroscopic data are interpreted and supported by quantum chemical calculations. We focus the attention on the Raman frequency changes, interpretable in terms of: (i) bridge length (conjugation length); (ii) bridge conformational structure; and (iii) electronic coupling between the terminal radical units with the bridge and through the bridge, which could delineate through-bond spin polarization, or spin delocalization. These items are addressed by using the "oligomer approach" in conjunction with pressure and temperature dependent Raman spectroscopic data. In summary, we have attempted to translate the well-known strategy to study the electron (charge) structure of π-conjugated molecules by Raman spectroscopy to the case of electron (spin) interactions via the spin delocalization mechanism.

Understanding optoelectronic properties of cyano-terminated oligothiophenes in the context of intramolecular charge transfer.

In this paper we have prepared a new series of oligothiophenes capped with hexyl groups and a variety of strong acceptors, mainly cyanovinyl moieties. An exhaustive analysis of the absorption, photophysical, electrochemical, solid state, nonlinear optical and vibrational properties has been presented guided by theoretical calculations. The investigation is centered on the efficiency of the intramolecular charge transfer (i.e., chain length and acceptor dependence) and its impact on all the relevant electronic, structural, optical, and vibrational properties. The most significant features imparted by the acceptors through the π-conjugated oligothiophene path are (i) intense visible electronic absorptions, (ii) tuned fluorescence wavelength emissions, (iii) solid state π-stacking, (iv) ambipolar redox behavior, (v) S(1) ⇝ S(0) internal conversion as being the major route for the deactivation of the excited state, and (vi) large electronic and vibrational contributions to their nonlinear optical response (hyperpolarizability). The analysis establishes connections between the different properties of the materials and structure-function relationships useful in organic electronics.