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Excitation/detection energy controlled anisotropy dynamics in asymmetrically cyano substituted tri-podal molecules
Authors: Seintis K | Kalis I-K | Klikar Milan | Bureš Filip | Fakis M
Year: 2020
Type of publication: článek v odborném periodiku
Name of source: Physical Chemistry Chemical Physics
Publisher name: Royal Society of Chemistry
Place: Cambridge
Page from-to: 16681-16690
Titles:
Language Name Abstract Keywords
cze Excitační/detekční energií kontrolovaná anizotropní dynamika u kyan-substituovaných tripodálních molekul. V této práci jsou studovány fotofyzikální vlastnosti dvou sérií asymetrických tripodálních molekul za účelem stanovení závislosti lokalizační/delokalizační energie na excitační a detekční vlnové délce pomocí fluorescenčních technik a femtosekundové anizotropní spektroskopie. intramolekulární přenos náboje; fotofyzikální vlastnosti; kvadrupolární chromofory; absorpční vlastnosti; dvoufotonová absorpce
eng Excitation/detection energy controlled anisotropy dynamics in asymmetrically cyano substituted tri-podal molecules In the present work, the photophysical properties of two series of asymmetrical tri-podal molecules are studied, in order to determine the dependence of energy localization/delocalization phenomena on excitation and detection wavelength, by means of steady state, femtosecond time-resolved fluorescence and anisotropy spectroscopy. The molecules bear triphenylamine as an electron donating core and an acetylenic or olefinic pi-conjugated bridge. At the periphery, they are substituted by no, one, two or three -CN groups used as electron acceptors. Thus, the compounds with only one or two -CN groups are asymmetrically substituted. As a comparison, the photophysics of their dipolar and quadrupolar analogues is also presented. The steady state absorption spectra of the asymmetrical tri-podal compounds exhibit a broadening and a low energy shoulder due to the splitting of the excited states. The fluorescence spectra are more red-shifted in the tri-podal molecules with a single -CN group, providing the first evidence of its mostly dipolar nature. Time-resolved anisotropy measurements by using different excitation and detection wavelengths provide clear evidence that the asymmetrical tri-podal molecules with one or two -CN groups behave like octupolar molecules upon high-energy excitation (the initial anisotropy is found 0.1-0.15), while upon low-energy excitation they reveal a behavior expected for linear dipolar or V-shaped quadrupolar molecules (the initial anisotropy is very close to 0.4 and 0.17, respectively). The symmetrical tri-podal compounds with no or three cyano groups, exhibit an anisotropy depolarization time of 2.5 ps attributed to energy hopping. The amplitude of this energy hopping component is wavelength dependent and increases as the excitation is shifted towards the long wavelength edge. intramolecular charge-transfer; photophysical properties; quadrupolar chromophores; absorption properties; 2-photon absorption

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