The capability to control charge transfer dynamics in a donor–acceptor molecule is important for efficient optoelectronic devices. Charge transfer dynamics is governed by thermodynamics of ...donor–acceptor charges in a given dielectric environment. Metamaterial structure has been shown to be able to control charge separation and charge recombination processes via nonlocal effect on dielectric permittivity for a fixed donor–acceptor distance organic film. Here, we report the influence of the metamaterial structure on the donor–acceptor distance dependence of the electron transfer process occurring in liquid crystalline organic semiconductor thin films. By examining the charge recombination rate in three different donor–acceptor distances, it is found that the barrier height β increases from 0.084 to 0.137 Å–1 by 63% in the presence of metal-dielectric multilayered metamaterial structures. Based on the Marcus theory on the charge transfer process, we show that a further increase in the driving force for a larger donor–acceptor distance is mainly responsible for the barrier height increase in the presence of a multilayered metamaterial substrate when compared with a glass substrate. This study will provide a significant step forward in enabling more efficient hybrid organic-optoelectronic devices associated with the charge transfer process.
We report on the demonstration of liquid organic dye lasers based on 9-(2-ethylhexyl)carbazole (EHCz), so-called liquid carbazole, doped with green- and red-emitting laser dyes. Both waveguide and ...Fabry-Perot type microcavity fluidic organic dye lasers were prepared by capillary action under solvent-free conditions. Cascade Förster-type energy transfer processes from liquid carbazole to laser dyes were employed to achieve color-variable amplified spontaneous emission and lasing. Overall, this study provides the first step towards the development of solvent-free fluidic organic semiconducting lasers and demonstrates a new kind of optoelectronic applications for liquid organic semiconductors.
The synthesis, characterization and (TD)-DFT calculations of the electrochemical and photophysical properties of novel ethynylene-analogues of hemicurcuminoids are described. These dyes are both ...emissive in solution and in the solid state. While compounds that emit through an efficient charge transfer (CT) state show solvatochromic behaviour associated with low fluorescence quantum yields, those lacking of donor groups show high fluorescence quantum yields of 70–80%, in solution. The latter dyes also present the advantage to emit in the solid state in the visible region with fluorescence quantum yields up to 23%. Their condensed phase spectrum can be bathochromically shifted to the near infrared region (742 nm) by appending a strong donor group.
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•Synthesis of new fluorophores based on hemicurcuminoid boron difluoride.•Photophysical study reveals strong emission of the dyes not containing charge transfer states.•Fluorescence properties of dyes in their condensed phase show aggregation induced emission.
A plasmonic chiral metamaterial is fabricated from a thin Au film and exhibits static optical rotatory power (ORP) in the visible spectral range. Transient ORP is measured to clarify the temporal ...development of ORP using a circularly polarized light (CPL) pump beam. Three distinct transient behaviors of ORP are identified, resulting from different energy relaxation processes of hot electrons that occur during a period of a few picoseconds after pumping. Nonthermal hot electrons experience Lorentz force from an inverse Faraday effect and electron–boundary scattering, yielding a pump beam CPL helicity‐dependent transient ORP. Once hot electrons are in thermal equilibrium with the lattice, electron energy is distributed among the occupied states, as described by Fermi–Dirac statistics. Moreover, the transient ORP is independent of pump beam CPL helicity, well explained by the selection rule of electron excitation and two‐temperature model of the electron cooling process. Theoretical analysis of the transient ORP in terms of the energy relaxation of thermal hot electrons is carried out by introducing a temperature‐dependent dielectric function and finite‐difference time‐domain simulation. It is found that the magnitude of ORP at an elevated temperature is reduced to less than that at room temperature, agreeing well with the experimental observation.
Time‐resolved pump–probe experiment is performed to measure ultrafast optical rotatory dispersion in a chiral metamaterial. Using a circularly polarized light pump beam, it is clarified that sub‐picosecond hot‐electron dynamics carry information regarding the handedness of chiral metallic inclusion of chiral metamaterial. Once thermalized, the transient optical rotatory dispersion is found to be independent of pump beam circularly polarized light helicity.
The photophysical properties of donor-acceptor (D-A) and donor-acceptor-donor (D-A-D) liquid crystalline dyads and triads based on two different discotic mesogens are examined in thin films by ...steady-state optical spectroscopy and subpicosecond transient absorption measurements. In these systems, triphenylene and perylene bisimide units are covalently linked by flexible decyloxy chain(s) and act as an electron donor (D) and acceptor (A), respectively. These discotic liquid-crystalline systems form well-separated D and A π-stacked columnar structures in thin films. The absorption spectra of the films indicate an aggregation of the perylene bisimide and triphenylene moieties along the columns. Steady-state photoluminescence measurements show a strong fluorescence quenching that is mainly attributed to a photo-induced charge transfer process taking place between the triphenylene and perylene bisimide units. Subpicosecond transient absorption measurements show that the photoinduced charge transfer (CT) states in the dyad and triad films are formed within 0.3 ps and recombine on a 150-360 ps time scale. In addition, a correlation between the dynamics of the charge recombination process and the spacing distances between D and A units can be established in the dyad and triad films. This study provides important information on the relationship between molecular packing and the charge transfer properties in such self-organized D and A columnar nanostructures.
Dynamics of the photo-induced charge transfer are correlated with the structural properties of self-assembled discotic donor-acceptor dyad and triad films.
A novel defect mode is realized in a three‐layered structure: a left‐handed cholesteric liquid crystal (CLC) layer sandwiched between right‐handed CLC films (see Figure). The defect states emerge, ...and the photonic density of state is resonantly enhanced when the defect mode coincides with the edge mode. The lasing from this enhanced mode is found to show a lower threshold value.
Light possesses both spin and orbital angular momentum (AM). While spin AM is determined by helicity of circular-polarization, orbital AM is characterized by topological charge of vortex beam. ...Interaction of AM with optical beam orbit leads to optical spin Hall or orbital Hall effect, exhibited as spin-dependent or topological charge-dependent transverse shift of optical beam. Conservation of AM enables spin-to-orbital AM conversion, where circular-polarized Gaussian beam is converted to opposite-helicity circular-polarized vortex beam with topological charge \(\pm 2\), an example of controlling spatial beam profiling by spin flip. However, the resultant vortex beam has the beam center of gravity unchanged, the same as that of incident Gaussian beam, meaning a null transverse shift. Here we introduce a cyclic group symmetric metasurface to demonstrate generation of vortex beam exhibiting spin-dependent transverse shift, namely, spin- and orbital-Hall effect, attributed to an alteration of dynamical phase of scattered beam according to the order \(n\) of cyclic group while keeping geometric phase constant. Capability of spin-controlled spatial beam profiling with a transverse shift via spin- and orbital-Hall effect has important implications for spatial demultiplexing in optical communication utilizing orbital AM mode division multiplexing as well as for optical vortex tweezer and signal processing involving vortex beams.
The authors have measured the electro-optic Kerr effect in the isotropic phase of a urea derivative. Electric-field-induced birefringence Deltan was observed in the isotropic phase even 30 degrees C ...above the isotropic-columnar phase transition temperature. The induced birefringence is inversely proportional to temperature, as predicted by the Landau-de Gennes theory. Two distinct regions are identified from the proportionality constants in the isotropic phase; optical second-harmonic generation (SHG) is easily observable in the low-temperature region on applying an electric field, whereas SHG activity does not emerge in the higher-temperature region. The structure of molecular assemblies is discussed based on these experimental results.
Block copolymers, 9-ethylcarbazolyl methacrylate (CzMA) with 3-nitro-9-ethylcarbazolyl methacrylate (NCzMA), and styrene with optically functionalized isocyanates containing disperse red 1 (DR1NCO) ...and (s)-(-)-2-methylbutanol (MBI), were prepared by anionic polymerization for photo-electronic materials. The living condition of CzMA was found at -78°C for 3 h with diethyl zinc and block copolymers of CzMA with NCzMA were synthesized successfully. The polymers show potential to be used as energy transfer materials in UV and PL spectra. Block copolymers of styrene with optically functionalized isocyanates were also synthesized with high yield and the polymers showed the large optical activity at 476 nm.
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