Determining long-lived photo-excited species in thin-film anthracene derivatives using quasi-continuous wavelength photo
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Determining long‑lived photo‑excited species in thin‑film anthracene derivatives using quasi‑continuous wavelength photo‑induced absorption Murat Aydemir1 Received: 14 April 2020 / Revised: 9 September 2020 / Accepted: 23 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Long-lived excited states dynamics of sky-blue emitting 9,10-bis [9-hexyl-6-((E)styryl)-9H-carbazol-3-yl] anthracene derivatives have been investigated by means of time-correlated single photon counting and quasi-continuous wavelength photoinduced absorption (QCW-PIA) spectroscopies. The QCW-PIA is a versatile tool to investigate the long-lived photo-excited species with lifetimes ranging from microsecond to millisecond time scale. In this time regime, mobile and trapped polarons were recognized, and their long and short mean lifetimes were estimated using a modulation frequency dependence technique at 20 K. Keywords Anthracene derivatives · Quasi-continuous wavelength photo-induced absorption · Long-lived photo-excited states
Introduction Pump–probe spectroscopy techniques help to get better understanding on variety of complex molecular interactions in organic [1] and inorganic [2] materials Especially, transient absorption [3] (TAS) and quasi-continuous wavelength photo-induced absorption [4] (QCW-PIA) spectroscopies were used to investigate the nature of excited species in π-conjugated polymers and different small molecules. QCWPIA spectroscopy is one of the brilliant techniques to study the long-lived photoexcitations, using a modulated laser beam (~ 100 mW/cm2). In working principal of QCW-PIA, the absorption of excited species is formed in the organic molecules by the pump beam and monitored by the probe beam. The differential change in absorption or transmission signals is monitored, and the observed signals are attributed as either photo-induced absorption (PIA) or photo-induced bleaching (PIB). With this * Murat Aydemir [email protected] 1
Department of Fundamental Sciences, Faculty of Science, Erzurum Technical University, Erzurum, Turkey
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Polymer Bulletin
spectroscopy technique, the excited state dynamics of the molecules can be investigated from microsecond to millisecond time scale [5]. The signals are commonly aroused by phase space filling after depopulation of the ground state of the molecule; therefore, the QCW-PIA signal typically becomes negative as given in Eq. 1,
∑ ΔT Ai (𝜆)Ni (wm )L (𝜆, t) = − T j
(1)
where λ, L, t, w, N and Ai are the probe wavelength, sample thickness, time, frequency, number of states and multiline cross section (CS), respectively. The CS may include several transitions at different energies that may be included in photoexcitation spectrum. QCW-PIA data with different temperatures usually give detailed information on transitions of newly formed excited species, which can be excitons, polarons or free charge carriers, [6] but in organic semiconductors, long-lived species are usually triplet states or charge carriers [7]. Ther
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