Elucidating structural roles in photoinduced charge transfer is indispensable, as nuclear rearrangements are simultaneously usually involved in the dynamics. However, it is hard to evaluate whether the structural changes occur or not by using conventional time‐resolved electronic spectroscopy. Here, time‐resolved impulsive stimulated Raman spectroscopy is applied to record the evolution of vibrational snapshots during charge‐separation dynamics of donor–acceptor–donor‐type quadrupolar perylene bisimide in real time. Drastic frequency shifts were observed for several Raman bands with their population kinetics, thus symmetry‐breaking charge separation accompanies significant structural changes, as supported by (TD)‐DFT calculations. A comparison between time‐resolved Raman spectra of the neutral S1 state and the radical anion species shows that the spectral signatures, especially in high‐frequency regions, provide important clues to bond length alternation patterns in the PBI core.
Herein, the ultrafast photoinduced dynamics and vibrational coherences for two perylenebisimide (PBI) H-aggregates showcase the formation of the excimer state and the delocalized radical anion state in the excited state, respectively. Using femtosecond transient absorption (fs-TA) and time-resolved impulsive stimulated Raman scattering (TR-ISRS) measurements, we unveiled excited-state dynamics of PBI H-aggregates in two aspects: (1) the intermolecular interactions between PBI units in Haggregates induce the formation of new excited states, excimer and delocalized radical anion states, and (2) the intermolecular out-of-plane along the aggregate axis and the PBI core CC stretch Raman modes can be a crucial indicator to understand the coherent exciton dynamics in H-aggregates. Notably, those excited-state Raman modes showed stationary peak positions during the excited-state dynamics. TR-ISRS analysis provides insights into the excited-state vibrational coherences concerning the formation of the excimer and charge-delocalized state in each aggregate system.
We report on the fabrication of organic light-emitting devices (OLEDs) using a thin NaCl interlayer as an electron-injection medium. The results show that the device containing the NaCl layer has a higher brightness and electroluminescent efficiency than the device without this layer. We also fabricated similar-structured comparable devices, which were prepared with a LiF layer as a different electron-injection medium. The maximum electroluminescent efficiency of the NaCl (1 nm)/Al cathode device was 2.85 cd/A, which is higher than the 2.25 cd/A of the LiF (1 nm)/Al cathode device. The ultrathin NaCl layer modified the carrier injection properties. In conclusion, the NaCl layer between a cathode and an emitting layer of OLEDs can be used as the carrier injection layer to improve the EL properties.
A bright near‐infrared (NIR) fluorescent molecule was developed based on the donor–acceptor–donor (D–A–D) approach using an aza‐BODIPY analog called pyrrolopyrrole aza‐BODIPY (PPAB) as an electron‐accepting chromophore. Directly introducing electron‐donating triphenylamine (TPA) to develop a D–A–D structure caused redshifts of absorption and emission of PPAB into the NIR region with an enhanced fluorescence brightness of up to 5.2×104 m−1 cm−1, whereas inserting a phenylene linker between the TPA donor and the PPAB acceptor induced solvatochromic behavior in emission. Transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge‐transfer state in the former case and the contribution of the dark charge‐separated state to the excited state in the latter case. The bright D–A–D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7 % and a low amplified spontaneous emission threshold of ca. 80 μJ cm−2, indicating the high potential for NIR optoelectronic applications.
Hexameric
and tetrameric porphyrin nanorings, Z6·T6 and Z4·T4, were synthesized
in 53% and 14% yields, respectively, by the Sonogashira-type self-oligomerization
of porphyrin monomer 1 using hexadentate template T6 and tetrapyridylporphyrin template T4. Template-free
nanorings Z6 and Z4 were also prepared.
The femtosecond transient absorption measurements revealed fast excitation
energy hopping (EEH) along these nanorings with hopping rates of 2–5
ps. Treatment of Z6 with chiral template CT6 gave Z6·CT6 showing circular dichroism
(CD) and circularly polarized luminescence (CPL) in the absorption
and fluorescence regions of Z6, respectively, which indicates
chirality transfer from CT6 to Z6.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.