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Inter/intrachain interactions behind the formation of charge transfer states in polyspirobifluorene: A case study for complex excited-state dynamics in different polarity index solvents

Aydemir, Murat; Jankus, Vigintas; Dias, Fernando B.; Monkman, Andrew P.

Authors

Murat Aydemir

Vigintas Jankus

Andrew P. Monkman



Abstract

In this work, we demonstrate the complex excited-state nature of the conjugated polymer, polyspirobifluorene (PSBF), using steady-state and time-resolved spectroscopy techniques to understand the origin of excited charge transfer state (CT) formation and their contribution to the total photoluminescence (PL). The measurements were compared in two solvents with different polarity, for example, methyl cyclohexane (MCH) and 2-methyltetrahydrofuran (2-MeTHF), which allow us to reveal solvent quality and temperature dependent CT state formation arising from “inter/intrachain” interaction phenomena. The inter/intrachain interactions are explained by means of spatial conformational changes of the polymer chain configuration, such as coiling and collapse of the backbone with concomitant side chain reorganization. It has been found that the PL emission at room temperature (RT) demonstrates a mixed state configuration containing contributions from 1(π, π*) excited states along with the CT states contribution, with the spectra arising from a mixture of the two emissive species. However, with decreasing temperatures to ca. 145 K (prior to the freezing point) in 2-MeTHF, the two emissive species become separated, with the emission from the CT state showing a red-shift with decreasing temperature. At 145 K, we observe the formation of an unstructured, wholly new emission band, which is strongly red-shifted relatively to the 1(π, π*) excited-state and shows classic Gaussian line shape. This emission is attributed to the formation of “inter/intrachain” CT states. In the case of frozen solutions (∼90 K), the spectra dramatically blue-shifts and loses all contribution from the “inter/intrachain” species, and emission then arises completely from the pure “intrachain” CT excitonic state. The behavior of the polymer is strongly dependent on both solvent quality and temperature effects on the excited state geometry relaxation by means of the local solvent–solute interactions that stabilize the CT states, due to solvation of the new charge distribution, and also changes on the transition states via manipulating energy barriers.

Citation

Aydemir, M., Jankus, V., Dias, F. B., & Monkman, A. P. (2015). Inter/intrachain interactions behind the formation of charge transfer states in polyspirobifluorene: A case study for complex excited-state dynamics in different polarity index solvents. Journal of Physical Chemistry C, 119(11), 5855-5863. https://doi.org/10.1021/jp512467g

Journal Article Type Article
Acceptance Date Feb 23, 2015
Online Publication Date Mar 3, 2015
Publication Date 2015-03
Deposit Date Jul 17, 2017
Journal Journal of Physical Chemistry C
Print ISSN 1932-7447
Electronic ISSN 1932-7455
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 119
Issue 11
Pages 5855-5863
DOI https://doi.org/10.1021/jp512467g