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 CC 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.

Replacement of the meso methine carbon atoms of porphyrins with heteroatoms is a powerful strategy for tuning their optical and electronic properties. In particular, 5‐oxaporphyrin is an attractive target due to its importance as an intermediate in heme catabolism. In this work, we describe the synthesis and properties of a free‐base 5‐oxaporphyrinium cation, which was prepared by the ring‐closure of a bilindione with trifluoromethanesulfonic anhydride. This free‐base 5‐oxaporphyrinium cation exhibits dual fluorescence originating from its unique NH tautomerism. In contrast to normal porphyrins, the cis form of the 5‐oxaporphyrinium cation is more stable than the trans form due to the effective delocalization of its positive charge. We thus demonstrate here that meso‐modified heteroporphyrins enable the manipulation of NH tautomerism in porphyrinic macrocycles.

Unsymmetrically fused porphyrins containing one or two naphthalimide subunits were prepared in modular syntheses relying on electron-rich and electron-poor pyrrole building blocks. These new chromophores show progressive changes in their electron-deficient character, while retaining comparably small optical and electrochemical band gaps. The intrinsic curvature and extended optical absorption of these systems make them of interest as mono- and difunctional components of multichromophoric assemblies.

For H-aggregates of perylene bisimide (PBI), it has been reported that upon photoexcitation, an initially delocalized Frenkel exciton is localized by excimer formation. However, in recent studies, the beforehand exciton dynamics preceding the excimer formation was suggested in larger aggregates consisting of at least more than 10-PBI subunits, which was not observed in small aggregates comprising less than four-PBI subunits. This feature implies that the size of molecular aggregates plays a crucial role in the initial exciton dynamics. In this regard, we have tried to unveil the initial exciton dynamics in PBI H-aggregates by tracking down the transient reorientations of electronic transition dipoles formed by interactions between the PBI subunits in systematically size-controlled PBI H-aggregates. The ultrafast coherent exciton dynamics depending on the molecular aggregate sizes can be distinguished using polarization-dependent femtosecond-transient absorption anisotropy spectroscopic measurements with a time resolution of ∼40 fs. The ultrafast decay profiles of the anisotropy values are unaffected by vibrational relaxation and rotational diffusion processes; hence, the coherent exciton dynamics of the PBI H-aggregates prior to the excimer formation can be directly revealed as the energy migration processes along the PBI H-aggregates.