3P-036
Ultrafast dynamics of novel aromatic micelles
encapsulating fluorescent dyes
(Molecular Spectroscopy Lab., RIKEN1, Chemical Resources Lab., Tokyo Tech2)○Matthew M Sartin1, Kei Kondo2, Michito Yoshizawa2, Tahei Tahara1[Introduction]
A recently-synthesized anthracene-embedded amphiphile (AEA) was shown toaggregate into anthracene-shelled micelles (ASM), as illustrated in Figure 1.1 These micelles
can encapsulate a hydrophobic fluorescent guest (e.g. DCM) in water. Steady-state
spectroscopy has shown that the chromophoric host can be photoexcited and subsequently
AEA structureNASMN
2ClOO

transfer energy to the guest, resulting inemission from the latter. In this study, we
examine the time-resolved fluorescence of
these materials to elucidate the dynamics ofFig. 1. Formation of ASM from AEA

this novel aromatic supramolecule.

[Experimental]
AEA and ASM were prepared as described previously.1 ASM was excited using 140
fs, 400 nm pulses. 500 nm pulses were used to excite DCM in solution or within micelles. The
resulting fluorescence transients were collected using a streak camera. Fluorescenceanisotropy data were collected by placing apolarizer in front of the camera to alternately
filter parallel and perpendicular light.
[Results]
Figure2shows

thesteady-state

fluorescence spectra of AEA, ASM, andencapsulated

DCM(i.e.,ASM⊃DCM

host-guest complex). A dilute solution of freeAEA
Fig. 2. Representative fluorescence spectra ofAEA, ASM, and encapsulated DCM.

inwateror

methanolexhibits

fluorescence primarily at short wavelengths,

which decays monoexponentially with a time constant of 6.5 ns. A solution of empty ASM inwater exhibits a bi-exponential fluorescence decay consisting of a 32-ns component, centeredat 500 nm, and 5.2 ns component, which is dominant at shorter wavelengths. The former isassigned to ASM fluorescence, and the latter is assigned to free AEA. Direct excitation of theencapsulated DCM within the ASM⊃DCM complex yields a fluorescence spectrum with apeak at 648 nm and a decay time constant of 3.6 ns.
PhotoexcitationoftheASM⊃DCM

complex at 400 nm, which primarily excites theASM

component,yields

thetransient

fluorescence spectra shown in Figure 3. The
bands with peaks at 630 and 450 nm areassignable to fluorescence from encapsulated
DCM and free AEA, respectively. Fluorescencefrom DCM is observable even at the earliest times,
Fig. 3. Transient fluorescence decays of
400-nm-excited ASM⊃DCM. The black andbrown lines represent the fluorescence of free
AEA and encapsulated DCM, respectively.

indicatingthatenergytransferwithintheASM⊃DCM complex is completed within the 25
ps time resolution of the present measurement.

The fluorescence anisotropy decays of empty ASM and encapsulated DCM were alsocollected to determine whether or not the guest rotates freely within the micelle. Thefluorescence anisotropy of encapsulated DCM decays with a time constant of 740 ps, which ismuch slower than the 100 ps observed for DCM in methanol. Therefore, its motion is highly
restricted in the micelle. Empty ASM shows an anisotropy decay time constant of 520 ps.
Since it is very unlikely that constrained DCM rotates more slowly than its host micelle, theorientation of DCM must be completely fixed within the micelle, so that the two rotate
together. Enlargement of the micelle upon encapsulation of DCM would account for theslower anisotropy decay of the complex.
[References]1

Kondo, K.; Suzuki, A.; Akita, M.; Yoshizawa, M. Angew. Chem. Int. Ed. 2013, 52, 2308.