Cyclodextrin-Isolated Alkynylpyrenes as UV-Stable and Blue-Light-Emitting Molecules Even in Condensed States

Abstract

Encapsulation of highly emissive alkynylpyrenes with permethylated α-cyclodextrin (PM-α-CD) followed by capping reaction yielded alkynylpyrene-based [3]rotaxanes. The [3]rotaxane emitted only blue light of monomeric pyrene under various circumstances such as lipophilic, hydrophilic, and even condensed states and exhibited extremely high stability for UV irradiation. These properties would result because PM-α-CD, like bulletproof glass, protected the alkynylpyrene core from the attack of another excited alkynylpyrene and singlet oxygen generated by the energy transfer from the excited alkynylpyrene.

Macroscopic Change in Luminescent Color by Thermally Driven Sliding Motion in [3]Rotaxanes

“…With a view to address this problem, we combined thermal diffusion in rotaxanes with chromophore insulation to control exciplex emission. Here, we design a rotaxane bearing a luminescent station in which the luminophore is insulated at low temperature . Rather than utilizing intramolecular interactions between the macrocycle and the station in the rotaxane, the emission color can be changed by exposing the luminescent station to external molecules, that is, by exciplex formation; at high temperature, macrocyclic sliding occurs, which induces intermolecular interactions between the excited luminophore and external molecules (Figure a).…”

“…Pyrene derivatives generally exhibit monomer emission upon photoexcitation, whereas this luminescence becomes an exciplex emission in the presence of donor molecules such as N , N ‐dimethylaniline (DMA), because of the formation of complexes between pyrene and DMA in the excited state . However, rotaxane structures can isolate such luminophores from external environments . In fact, the pyrene moiety in the S[3]R structure with a short axle distance was demonstrated to be completely protected from external molecules by the two PMαCDs.…”

“…[16] However,r otaxane structures can isolate such luminophores from external environments. [14,15] In fact, the pyrene moiety in the S[3]R structure with as hort axle distance was demonstrated to be completely protected from external molecules by the two PMaCDs. In this study,t he length of the ethylene glycol axle in this rotaxane was systematically tuned to achieveathermally driven switching system in which the luminophore is protected by PMaCDs at low temperature, to displaym onomer emission, [15] but is exposed to DMA at high temperature, to exhibit exciplex emission.…”

“…Here, we design ar otaxane bearing al uminescent station in which the luminophorei si nsulated at low temperature. [14,15] Rathert han utilizingi ntramolecular interactions betweent he macrocycle and the station in the rotaxane, the emission color can be changed by exposing the luminescent station to external molecules, that is, by exciplex formation;a th igh temperature, macrocyclic sliding occurs, which induces intermoleculari nteractions between the excitedl uminophore and external molecules ( Figure 2a). After luminescent emission, the luminophore at the steady state needs to be shielded once more from the externalm olecules.…”

“…The [3]rotaxane S [3]R (n = 0) was synthesized accordingt oa previously reported procedure; [15] in this notation, n determines the chain and rotaxanea xle length (Figure 2b). In addition, [3]rotaxanes with longer ethylene glycol axles, M[3]R (n = 2) and L[3]R (n = 5), were prepared.…”