Probing the Intrachain and Interchain Effects on the Fluorescence Behavior of Pentiptycene-Derived Oligo(p-phenyleneethynylene)s

Abstract

The synthesis, crystal structure, and fluorescence behavior of acetylene-bridged pentiptycene dimer (2), trimer (3), and tetramer (4) are reported. For comparison, a phenylene-pentiptycene-phenylene three-ring system (5) is also investigated. As a result of the unique intrachain pentiptycene-pentiptycene interactions in 3 and 4, their twisted conformers are populated in polar solvents and at low temperatures, and the phenomenon of nonequilibration of excited rotational conformers is observed. Twisting of the pi-conjugated backbones leads to blue-shifted absorption and fluorescence spectra and increased fluorescence quantum yields and lifetimes. The fluorescence spectra of 2-4 undergo small red shifts but large intensity variations in the 0-1 vs 0-0 bands on going from solutions to thin solid films, which can be accounted for by the reabsorption effect. However, the reduction in fluorescence quantum yields for 2-4 in films vs solutions is mainly attributed to efficient interchain exciton migration to nonfluorescent energy traps. In contrast, the behavior of nonequilibration of excited rotamers is not observed for 5 in solutions. Compound 5 forms J-type aggregates through terminal phenylene pi-stackings in the solid state, resulting in a new absorption band at 377 nm and large red shifts of the structured fluorescence spectra.

Pentiptycene‐Derived Oligo(p‐phenyleneethynylene)s: Conformational Control, Chain‐Length Effects, Localization of Excitation, and Intrachain Resonance Energy Transfer

“…The twisted excited state can be generated and captured by selective excitation of the twisted conformers with shortwavelength light (e.g., 302 nm) in a 2-methyltetrahydrofuran (MTHF) glass at 80 K. This procedure relies not only on the neighboring noncovalent pentiptycene-pentiptycene interactions that favor the twisted form at low temperatures, but also on the large resistance to rotation of the pentiptycene groups in a frozen glass. One particularly interesting but unexplained observation [12] is the same fluorescence profiles recorded for the twisted excited states of 1 and 2 (see below), despite their different chain lengths. We postulated that this observation is due to localized excited states with the excitation confined in a common segment, as the calculated torsion angle (ca.…”

“…[5, 6] It is also widely accepted that a flexible CP chain can be considered as an ensemble of chromophores of different lengths because of the conformational disorder of large torsion angles, [7] and, consequently, excitation delocalization is dominated by resonance energy transfer (ET; Förster-type energy transfer or hopping) among the chromophores. [8] Recent quantum chemical calculations further revealed that a medium torsion angle ( 508) is sufficient to confine the excitation within a short subunit of CPs.[9] Nevertheless, the concept of torsion-induced localization of excitation and the resulting intrachain ET have not yet been verified with structurally well-defined conjugated oligomers, presumably because of the difficulties in conformational control [10] and in prevention of excited-state torsional relaxation [11] for the twisted conformers.Our recent work [12,13] on the pentiptycene-derived oligo(p-phenyleneethynylene)s (OPEs) 1 and 2 have revealed that these systems are excellent candidates for investigation of the concept of torsion-induced localization of excitation. Two distinct fluorescing states, which correspond to excited conformers of small and large torsion angles, have been identified for both 1 and 2.…”

Magnetic properties of two-dimensional hydrocarbon networks of sp2 and sp3 C atoms

“…Recent experiments reported the polymerized and oligomerized networks of iptycene as networks consisting of sp 2 and sp 3 C atoms [33,34]. Furthermore, a honeycomb architecture composed of triptycene connected via NH bridges [35] has been synthesized.…”

Multicolor Fluorescence Writing Based on Host–Guest Interactions and Force‐Induced Fluorescence‐Color Memory

“…Indeed, the as-prepared solid 1 formed fluorescent exciplexes with as eries of aniline derivatives with af luorescence color ranging from greenish yellow to reddish orange.A"black" color was also created by fuming with benzoquinone because of fluorescence quenching.More importantly,mechanical forces not only cause acrystalline-toamorphous phase transition in both the pristine and guestadsorbed solids,thus leading to the MFC properties,but also impose a"memory" of the resulting color,which is the key for multicolor fluorescence writing. Compounds 1 and 2 were readily synthesized through Sonogashira coupling reactions with commercially available 9,10-dibromoanthracene and the known building blocks ethynylpentiptycene [8] and ethynylbenzene [9] (see the Supporting Information for detailed synthetic procedures and compound characterization data). Thepristine solid 1 showed ag rinding-induced change in the color of fluorescence from green (G-form) to yellowish green (YG-form) with fluorescence maxima (l fl )a t5 06 and 540 nm, respectively (Figure 2a).…”

“…[7,8] We also expected that al oose crystalline packing might facilitate the occurrence of force-induced phase transitions and thus the Figure 1. Multicolor fluorescence drawing of an apple, an orange, and ab anana on athin powder film of 1 on glass.…”