Exciplex Emission and Förster Resonance Energy Transfer in Polycyclic Aromatic Hydrocarbon-Based Bischromophoric Cyclophanes and Homo[2]catenanes

Abstract

Energy transfer and exciplex emission are not only crucial photophysical processes in many living organisms but also important for the development of smart photonic materials. We report, herein, the rationally designed synthesis and characterization of two highly charged bischromophoric homo[2]catenanes and one cyclophane incorporating a combination of polycyclic aromatic hydrocarbons, i.e., anthracene, pyrene, and perylene, which are intrinsically capable of supporting energy transfer and exciplex formation. The possible coconformations of the homo[2]catenanes, on account of their dynamic behavior, have been probed by Density Functional Theory calculations. The unique photophysical properties of these exotic molecules have been explored by steady-state and timeresolved absorption and fluorescence spectroscopies. The tetracationic pyrene−perylene cyclophane system exhibits emission emanating from a highly efficient Forster resonance energy transfer (FRET) mechanism which occurs in 48 ps, while the octacationic homo[2]catenane displays a weak exciplex photoluminescence following extremely fast (<0.3 ps) exciplex formation. The in-depth fundamental understanding of these photophysical processes involved in the fluorescence of bischromophoric cyclophanes and homo[2]catenanes paves the way for their use in future bioapplications and photonic devices.

Odd–Even Effect in Charge Transfer Complexes through the Regulation of the Alkyl Chain

“…Thus, the energy transfer from TCNPh to the CT complex should be the reason that the strong CT emission was achievable even with small ratios of TAT-nC (Figure 4f). 84,85 These results indicated that the strategy for regulating the molecular arrangement through alkyl chains has no relation to the mixing ratio of the donor and acceptor.…”

Synthesis and Properties of Novel Alkyl-Substituted Hexaazacyclophanes and Their Diradical Dications

“…Conjugated molecules or ions not only have special physical characteristics such as strong nonlinear photoelectric properties, but they are also important in the study of novel materials, including polymer batteries, electronic conductors, and organic light-emitting devices. Among them, cyclic compounds have excellent optoelectronic properties, and their open-shell singlet ground-state double radicals have strong electron coupling characteristics and broad application prospects in magnetic devices [ 6 , 7 , 8 ]. In the past decade, the use of the para -connected phenyl ring as a scaffold for carbon-based materials sparked a research frenzy in the synthesis of cyclic compounds [ 9 , 10 , 11 , 12 ].…”

The Delayed Box: Biphenyl Bisimide Cyclophane, a Supramolecular Nano-environment for the Efficient Generation of Delayed Fluorescence

“…Significant advancements were made by Adachi and co-workers by designing spatially separated donor–acceptor systems for TADF. , Hitherto, this design principle has mainly been exploited in covalent molecular systems that often suffer from arduous syntheses with meager reaction yields and aggregation-caused quenching. A promising alternative approach is the non-covalent supramolecular strategy, where specifically tailored subunits provided by the host and the guest afford desirable photofunctional properties in their host–guest complexes. − A first very successful example for this approach was recently reported by Wong and Chou where the stabilization of triplet excitons and exploration of photofunctional properties from purely organic triplet generators in solution have been accomplished with the help of a guest embedded in a host cage, leading to solid-state materials with excellent OLED performance . However, in this system, the binding strength between host and guest in solution remained low compared to cyclophane-based host–guest systems, , and TADF properties could only be studied in a reliable way in the solid state, like for other donor–acceptor TADF systems relying on the non-covalent approach. − Further, activating the triplet harnessing pathways via a non-covalent strategy using organic chromophores remains a formidable challenge because, in addition to a sufficient binding strength, such a heavy atom-free, purely organic solution-state triplet generator demands an efficient triplet state population, a low singlet–triplet energy gap (Δ E S–T ), and its stabilization from vibrational dissipation and oxygen quenching.…”