Solvent-dependent intramolecular charge transfer delocalization/localization in multibranched push-pull chromophores

Abstract

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A Study of Excitation Delocalization/Localization in Multibranched Chromophores by Using Fluorescence Excitation Anisotropy Spectroscopy

“…In this work, we report the fluorescence excitation and fluorescence excitation anisotropy spectra of three multibranched push–pull molecules in a polymer matrix to probe the intramolecular redistribution of the excitation energy among the multibranched chromophores. Our results directly reflect the interplay between the chromophores, and hence, allow the excitation localization/delocalization in multibranched chromophores to be determined . Three typical dimer compounds (shown in Scheme ) were used to investigate excitation localization/delocalization.…”

“…The G factor measures the ratio of the sensitivities of the detection system for vertically and horizontally polarized light and is determined using horizontally polarized excitation: . To avoid fast rotation of the molecule during the fluorescence lifetime, these dimers were immobilized in a nonpolar Zeonex E48R (Zeon, Japan) film during fluorescence excitation anisotropy measurements, where a nonpolar matrix was used to keep the maximal degree of delocalization in coupled dimers, as the symmetry and intramolecular charge transfer (ICT) of multibranched chromophores are very sensitive to their surrounding environments . Meanwhile, the rigid matrix prevents the rotation of the chromophores within the excited‐state lifetime.…”

“…where the two subscripts, VV and VH, indicate the orientation (V = vertical, H = horizontal) of the excitation and emission polarizers, respectively.T he G factor measures the ratio of the sensitivities of the detection system for vertically and horizontally polarized light and is determined using horizontally polarized excitation: G ¼ I HV =I HH .T oavoid fast rotation of the molecule during the fluorescence lifetime, these dimers were immobilized in an onpolar Zeonex E48R (Zeon, Japan) film during fluorescence excitation anisotropy measurements, where an onpolar matrix was used to keep the maximal degree of delocalization in coupled dimers, as the symmetry and intramolecular charge transfer (ICT) of multibranched chromophores are very sensitive to their surrounding environments. [23,24,40] Meanwhile, the rigid matrix prevents the rotation of the chromophores within the excited-state lifetime. In this case, for the single branched structure of TPA-BT (a dipolar chromophore having parallel absorption and emission transition dipole moments), the anisotropy value has ar oughly constant value of around 0.4, this means that the depolarization effects, due to ori-…”

“…Our results directly reflect the interplay between the chromophores, and hence,a llow the excita-tion localization/delocalization in multibranched chromophores to be determined. [23,24] Three typical dimer compounds( shown in Scheme 1) were used to investigate excitation localization/ delocalization.T he compound 1,3,5-triethynyl benzene-dithienyldiketopyrrolopyrrole-2,2':5',2''-terthiophene (TA-DPP-TT) was prepared by linking dithienyldiketopyrrolopyrrole (DPP) via meta-substituted phenyl rings, [25] whereas both triphenylamine-benzo [1,2,5]thiadiazole (TPA-BT) and triphenylaminebenzothiadiazole-(4-hexyl)thiophene( TPA-BT-4HT) bear ac ommon electron-donating moiety in the central part, which is connected either side to electron-withdrawing groups through conjugated linkers. [26,27] Compared with TPA-BT,t he chromophores in TPA-BT-4HT are additionally terminated by thiophene groupst oi ncreaset he transition dipole moments of the monomers, owing to extended conjugation.…”

Star‐Shaped Push‐Pull Molecules with a Varied Number of Peripheral Acceptors: An Insight into Their Optoelectronic Features

“…Finally, the spectrum of 1 d is further red‐shifted to 390 nm but a high energy shoulder is observed at 373 nm (3.32 eV). According to the Frenkel exciton model, splitting of the excited state in tripodal compounds with C 3 symmetry leads to two degenerate states lying energetically lower than the monomer state as well as to a high energy one which has a vanishing oscillator strength ,,,. In our case, however, the high energy shoulder in the absorption of 1 d , is ascribed to this high energy state that has a non‐vanishing oscillator strength due to the D 3 group of symmetry of 1 d .…”