Ultrafast Broadband Transient Absorption and Circular Dichroism Reveal Relaxation of a Chiral Copolymer

Abstract

We present a study of the photoinduced dynamics of the chiral polyfluorene-phenylene copolymer PFPh in THF and in cholesteric thin films. After photoexcitation at 370 nm in THF, ultraviolet–visible–near-infrared (UV–vis–NIR) transient absorption spectra show fast subpicosecond to picosecond intrachain migration of singlet excitons, solvation dynamics, and an exciton lifetime of 410 ps. The PFPh thin film features also interchain singlet exciton migration and exhibits shorter (2.1 and 240 ps) and longer lifetime components (2800 ps, interchain recombination). Furthermore, a setup for ultrafast UV–vis broadband transient circular dichroism (TrCD) spectroscopy has been developed. Fast supramolecular relaxation processes are observed, which are linked to changes in the anisotropic polarizability and pitch length of the cholesteric film. Such combined ultrafast transient CD and absorption experiments hold promise to reveal not only details of relaxation processes in supramolecular arrangements but also structural rearrangements of chiral molecular systems featuring CD signals in the UV–vis region.

Coherent acoustic phonon dynamics in chiral copolymers

“…60 fs. Ultrafast transient circular dichroism (TrCD) spectra of PFPh were obtained on a setup, which was described in detail previously 24 . Briefly, a multifilament supercontinuum was generated using 400 nm seed pulses of either left-handed or right-handed circular polarization.…”

Mapping the broadband circular dichroism of copolymer films with supramolecular chirality in time and space

“…In this work, we present an advanced setup for TrCD detection using a Pockels-cell-based polarisation-switching design employing a deuterated KDP crystal (replacing the previously used BBO 24 , 25 ). Consequently, the time resolution is improved to 100 fs, with the two decisive benefits of a substantial increase in the intensity of the circularly polarised multifilament supercontinuum over the spectral range covered (260−700 nm) and an accompanying reduction of its intensity fluctuations.…”

Circular Polarization of Luminescence as a Tool To Study Molecular Dynamical Processes

“…Experimental and theoretical methods to study the influence of the dynamic coupling between electrons and nuclei are just emerging. [290] Further development of experiment techniques for circular polarization measurement with high spectral resolution [291] and ultrafast time resolution [292,293] may allow us to follow the dynamics of the molecules in more detail either Fourier transformed in the spectral domain or resolved in real time.…”