Dual fluorescence of 9-anthryl-substituted oligothiophenes in nonpolar environment

Abstract

9-Anthryl-oligothiophenes (9A-T., n= l-4) have been studied in n-hexane solution between helium and room temperature using absorption, fluorescence emission and excitation spectra and time resolved fluorescence measurements. These compounds are reference systems for studies on intramolecular energy and charge transfer in donor/acceptor-substituted conjugated chain molecules. The absorption spectra show contributions of both substituents anthracene and oligothiophene, but no additional bands due to mixed electronic states. Dual fluorescence is observed at T, 120 K for the compounds 9A-T, (n= l-3), but not for 9A-T+ Time resolved spectroscopy reveals a dynamical coupling between the two emission components whose relative quantum yields are strongly temperature dependent. The occurrence of the dual fluorescence is explained by an intramolecular torsional motion between the two molecular subunits.

Dual Emission: Classes, Mechanisms, and Conditions

“…[110] In ESCE-type DE compounds,t wo emitting states are reached from the initial FC state by parallel relaxation [111] or, more commonly,b ys equential relaxation [112][113][114][115][116][117][118] (see Figure 7). The"FC-like" [110] short wavelength (SW) state is twisted, as in PNI [110] or 3Ac-3T, [118] or bent, as in COT [113] or in DPAC [115] (see Figure 7);D PACs hows sub-stantial ICT character.T he relaxed long-wavelength state LW with extended conjugation is reached via afinite,but thermally accessible barrier through large amplitude rotor and/or bending motion (see Figure 7). Ty pically,t his leads to significant dependence on temperature,viscosity,pressure,and polarity, as indeed demonstrated for the examples in Figure 7.…”

“…Conversely,atlow temperatures and in viscous media, the SW/LWr atio increases. [111,113,118,121] This is due to inhibition of the aforementioned large-amplitude motions,w hich promote the path towards LW.A tt he same time, F F usually increases, [111] as this restricts the path towards the CI, which in turn leads to nonradiative decay. [17] Interestingly,t he slow planarization in ESCE compounds has been recently used to dynamically regulate energy/electron transfer processes in D-A dyads with DPAC as the donor moiety.…”

“…[108],C opyright2 016, American ChemicalS ociety,doi.org/10.1021/acs.jpclett.6b01185. [110] COT = cyclooctatetraene, [113] 3Ac-3T = 9anthry-terthiophene, [118] and DPAC = 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine, [115] with the side view from the X-ray structure (CCDC 837117) also shown. Red arrows indicate the large amplitudem otions on the path to the lower emitting state.…”

Fluorescence depolarization in organized media. Two-excited-state reactions controlled by orientation-dependent kinetic rates. I. Theory

“…Ph (1,2) (t) and Ph (2,1) (t) show a initially rising multiexponential evolution because the emitting states 2 and 1 are the transient excited states ͑i.e., they are pumped through the primary excited states 1 and 2, correspondingly͒. Similarly, the fluorescencedetected time-dependent excited-state order parameters ͗D 00 ( j) ͘ ex,k→ (t) of rank jϭ0, 2,4,6,8,10,12 are shown in Figs. 1͑d͒ and 1͑e͒ are shown the time evolutions of the first two terms in expansion ͑33͒.…”

Sulfur‐Containing Oligomers

“…(1 lo)]. In addition, anthryl-oligothiophenes and oligothienylporphyrins representing models for the donor-chain and the chain-acceptor, respectively, were included and synthesized by the same methodology [269]. Despite direct connection of the endgroups with the oligothiophene bridge, the electronic interactions of the anthracene and porphyrin moieties are weak.…”