Optical probes of excited states in poly(p-phenylenevinylene)

Solid state effects on exciton states and optical properties of PPV

We perform ab initio calculations of optical properties for a typical semiconductor conjugated polymer, poly-para-phenylenevinylene, in both isolated chain and crystalline packing. In order to obtain results for excitonic energies and real-space wave functions we explicitly include electron-hole interaction within the density-matrix formalism. We find that the details of crystalline arrangement crucially affect the optical properties, leading to a richer exciton structure and opening nonradiative decay channels. This has implications for the optical activity and optoelectronic applications of polymer films.

Ultrafast spectroscopy of even-parity states in pi-conjugated polymers

Relaxation dynamics of even parity ( A(g)) states in poly( p-phenylene vinylene) derivatives are studied using a novel fsec transient spectroscopy, in which two different excitation pulses successively generate odd parity ( 1 (1)B(u)) excitons at 2.2 eV and then reexcite them to higher A(g) states. For reexcitation energies Planck's over 2piomega<1.1 eV ultrafast internal conversion back to 1 (1)B(u) takes place in accordance with Vavilov-Kasha's rule. However, for Planck's over 2piomega>1.1 eV the decay occurs in a nonemissive state identified as a polaron pair, showing that the A(g) states above 3.3 eV mediate charge transfer.