Effects of aggregation on the excitation transfer in perylene-end-capped polyindenofluorene studied by time-resolved photoluminescence spectroscopy

Abstract

We have investigated the excitation transfer in a system comprising poly(6,6Ј,12,12Ј-tetra-2ethylhexyl-2,8-indenofluorene͒ ͑PIFTEH͒ chains end-capped with perylene dye molecules, using femtosecond time-resolved photoluminescence ͑PL͒ spectroscopy as well as polarized photoluminescence measurements. The transfer of excitons from isolated PIFTEH chains to perylene molecules is completed within the first 30-40 ps after excitation, and we extract a Förster radius R 0 ϭ(1.8Ϯ0.3) nm from the time-resolved PL transients. We have modelled the polarization anisotropy for a guest-host system subject to Förster interactions via a Monte Carlo simulation and find that the emission from acceptors becomes unpolarized at sufficiently large acceptor concentrations, permitting an accurate determination of the Förster radius from time-integrated photoluminescence anisotropy measurements. While spectral overlap calculations predict a large efficiency for the transfer of excitations to the perylene molecules from sites where the PIFTEH chains aggregate, no transfer is observed experimentally, which we attribute to chain packing effects within the sample prohibiting sufficiently close contact between PIFTEH aggregates and perylene molecules.

Femtosecond hot-exciton emission in a ladder-typeπ-conjugated rigid-polymer nanowire

“…[22][23][24][25][26][27][28][29][30][31][32][33] Obviously, there is a clear gap between (i) and (ii): in the frequency domain, this gap appears as a large shift from the excitation λ ex to the onset of λ em , as shown in Fig. 1, which corresponds to initial hot-exciton cooling.…”

“…6 If excitation occurs yielding a large E K , any resultant emission from the hot excitons will lie underneath the strong linear absorption band; therefore, its intensity will be very weak, and it is usually not expected to be observed in experiment. [1][2][3][4][5][6][7][8][20][21][22][23][24][25][26][27][28][29][30][31][32][33] In the time domain, this gap represents a period between T * 2 and ∼3 ps. To date, no one has explored the physical processes of hot excitons in π -conjugated polymers because of this.…”

“…To date, no one has explored the physical processes of hot excitons in π -conjugated polymers because of this. [1][2][3][4][5][6][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Femtosecond pump-probe techniques are of little use here due to the superposition of stimulated emission from the hot exciton with photoinduced absorption to high-lying excited states; [2][3][4][5]23,[34][35][36][37][38][39] there are also limitations on the availability of the deep-blue spectral component from the white-light supercontinuum needed as a probe. [34][35][36][37][38][39] 045308-1 1098-0121/2013/87(4)/045308 (9) ©2013 American Physical Society In pristine thin films, π -conjugated polymers are typically amorphous glasses, having a statistical distribution of chain lengths and random orientations, and each chain usually is composed of multiple segments due to chain folding, twisting, kinks, or chain defects, etc., and all of these yield poorly resolved absorption and emission spectra and provide a large heat bath to enable excitons to migrate nondispersively over relatively large distance during their lifetimes.…”

“…[34][35][36][37][38][39] 045308-1 1098-0121/2013/87(4)/045308 (9) ©2013 American Physical Society In pristine thin films, π -conjugated polymers are typically amorphous glasses, having a statistical distribution of chain lengths and random orientations, and each chain usually is composed of multiple segments due to chain folding, twisting, kinks, or chain defects, etc., and all of these yield poorly resolved absorption and emission spectra and provide a large heat bath to enable excitons to migrate nondispersively over relatively large distance during their lifetimes. [1][2][3][4][5][6][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Moreover, the rich vibronic modes and the strong electron-phonon coupling on each single chain greatly broaden the overall optical transition cross sections in absorption and emission. [1][2][3][4][5][6][20][21][22][23][24]…”

“…[1][2][3][4][5][6][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Moreover, the rich vibronic modes and the strong electron-phonon coupling on each single chain greatly broaden the overall optical transition cross sections in absorption and emission. [1][2][3][4][5][6][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]…”