Photoexcitations in pernigraniline: Ring-torsional polarons and bond-order solitons

Abstract

We report the near-steady-state and long-time photoinduced spectroscopies of pernigraniline base, a novel Peierls ground-state polymer with multiple order parameters. Two kinds of defects are distinguished by differing time domains, ir-active vibrations, and light-induced electron spin resonance (LESR). The short-lived defect has a lifetime of msec scale, defect mass of ~~5m e , and is spinless; in contrast, the long-lived defect (mass -30Qm e ) has a lifetime of greater than several hours at low temperatures and spin j. We propose the short-lived excitation is a soliton defect in the bond-length order parameter, while the long-lived excitation is a polaronlike defect in the ring-torsion-angle order parameter.

Neutral soliton formation and disorder in pernigraniline base

“…2(a) The PA near 1.5 eV, which was reported earlier as having an associated charge and spin 1/2 [10], is consistent with the formation of an electron polaron [9]. The energy levels associated with the corresponding hole polaron are calculated to be near the valence and conduction band edges [9], and could be obscured by the significant subgap absorption due to disorder that is observed in PNB.…”

“…The successful synthesis [5,6] of pernigraniline base (PNB) provides the first degenerate ground state quasi-one-dimensional polymer beyond trans-polyacetylene [trans-(CH)~] that, in principle, can support solitons [7 -9]. Charged solitons have recently been observed in this system [10]. In this Letter, we report the photogeneration of confined neutral solitons in PNB.…”

Kinetic Mass of RT-BO Defect States in a Pernigraniline-Base Polymer

“…This E g is consistent with the 2.3 eV intensive peak of absorption in the PNB polymer [11], and a quantum-chemistry calculation [6] supports the angles. With the parameter set, we have got numerical solutions of the BO relaxation fujg and RT relaxation fYjg for charged Bo±RT polarons and BO±RT solitons through the self-consistent variational calculations [8,9].…”

“…RT relaxation dominates the effective mass of coupled defects. Experimentally, very small infrared active vibration modes indicate a large polaron mass [11,12]. Our theory showed the origin of the large defect mass.…”

Dynamic interaction between polarons and torsional vibrations in conjugated polymers

“…Extensions of this model to include ring-rotational degrees of freedom has been applied to pernigraniline [3] and poly(3-hexyl)thiophene (P3HT) [4]. Bond length and ringtorsion angle dimerizations were found to give rise to two types of topological defects, which explains features in photoinduced vibrational spectra [5].…”