Evidence for Excimer Photoexcitations in an Ordered {\pi}-Conjugated Polymer Film

TL;DR

This study investigates pressure effects on excitations in ordered and disordered poly(para-phenylenevinylene) films, revealing evidence for excimer photoexcitations in ordered films through transient photomodulation and theoretical calculations.

Contribution

It provides experimental and theoretical evidence for excimer photoexcitations in ordered polymer films, highlighting differences in exciton binding energies between ordered and disordered states.

Findings

Ordered films exhibit pressure-sensitive midinfrared PA bands attributed to excimers.

Disordered films show weak pressure dependence, linked to intrachain excitons and polarons.

Ordered films have reduced exciton binding energy due to new energy states below the continuum.

Abstract

We report pressure-dependent transient picosecond and continuous-wave photomodulation studies of disordered and ordered films of 2-methoxy-5-(2-ethylhexyloxy) poly(para-phenylenevinylene). Photoinduced absorption (PA) bands in the disordered film exhibit very weak pressure dependence and are assigned to intrachain excitons and polarons. In contrast, the ordered film exhibits two additional transient PA bands in the midinfrared that blueshift dramatically with pressure. Based on high-order configuration interaction calculations we ascribe the PA bands in the ordered film to excimers. Our work brings insight to the exciton binding energy in ordered films versus disordered films and solutions. The reduced exciton binding energy in ordered films is due to new energy states appearing below the continuum band threshold of the single strand.