▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

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Proton-Coupled Electron Transfer

Switches, and Actuators Masahiro Irie,*,† Tuyoshi Fukaminato,‡ Kenji Matsuda, and Seiya Kobatake †Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan ‡Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020, Japan Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan

Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators

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The π → π* transitions of more than 100 organic dyes from the major classes of chromophores (quinones, diazo, ...) have been investigated using a Time-Dependent Density Functional Theory (TD-DFT) procedure relying on large atomic basis sets and the systematic modeling of solvent effects. These calculations have been performed with pure (PBE) as well as conventional (PBE0) and long-range (LR) corrected hybrid functionals (LC-PBE, LC-ωPBE, and CAM-B3LYP). The computed wavelengths are systematically guided by the percentage of exact exchange included at intermediate interelectronic distance, i.e., the λmax value always follows the PBE > PBE0 > CAM-B3LYP > LC-PBE > LC-ωPBE > HF sequence. The functional giving the best estimates of the experimental transition energies may vary, but PBE0 and CAM-B3LYP tend to outperform all other approaches. The latter functional is shown to be especially adequate to treat molecules with delocalized excited states. The mean absolute error provided by PBE0 is 22 nm (0.14 eV) wit...

TD-DFT Performance for the Visible Absorption Spectra of Organic Dyes: Conventional versus Long-Range Hybrids

Solid state emitters based on excited state intramolecular proton transfer (ESIPT) have been attracting considerable interest since the past few years in the field of optoelectronic devices because of their desirable unique photophysical properties. The photophysical properties of the solid state ESIPT fluorophores determine their possible applicability in functional materials. Less fluorescence quantum efficiencies and short fluorescence lifetime in the solid state are the shortcomings of the existing ESIPT solid state emitters. Designing of ESIPT chromophores with high fluorescence quantum efficiencies and a long fluorescence lifetime in the solid state is a challenging issue because of the unclear mechanism of the solid state emitters in the excited state. Reported design strategies, detailed photophysical properties, and their applications will help in assisting researchers to overcome existing challenges in designing novel solid state ESIPT fluorophores for promising applications. This review highlights recently developed solid state ESIPT emitters with focus on molecular design strategies and their photophysical properties, reported in the last five years.

Excited-state intramolecular proton-transfer (ESIPT)-inspired solid state emitters

The cyclization and cycloreversion reactions of diarylethene derivatives have been studied with picosecond time-resolved Stokes and anti-Stokes Raman spectroscopies. The cyclization reaction of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (DMTF) is found to occur within 4 ps to produce the vibrationally excited closed forms in the ground electronic (S0) state. The time constant of the vibrational relaxation toward a thermal equilibrium with solvent molecules is estimated to be about 10 ps. The cycloreversion reaction of 1,2-bis(3,4-dimethyl-5-phenyl-2-thienyl)perfluorocyclopentene (DMPTF) also generates the vibrationally excited open forms in the S0 state within 4 ps, which decay on a picosecond time scale. The picosecond time-resolved anti-Stokes Raman spectra of DMPTF show two vibrational bands assignable to the CC stretching modes of the cyclopentene and thiophene moieties of the generated open forms. The Raman intensity arising from the cyclopentene moiety relative to that from the thiophene m...

Picosecond Time-Resolved Stokes and Anti-Stokes Raman Studies on the Photochromic Reactions of Diarylethene Derivatives

The laser fluorescence excitation spectrum and the single vibronic level fluorescence spectra from the \ ildeA1B2 state of tropolone have been measured in a supersonic free jet. Some vibronic bands observed in the region of 270–450 cm−1 from the 000 band have been assigned. A tunneling doublet separation for the ν′14 in-plane ring deformation mode has been measured to be 30 cm−1, which is significantly larger than 19 cm−1 for that for the zero-point level, suggesting that the average geometry of the ν′14 mode deviates significantly from that of the zero-point level.

The Electronic Spectra of Jet-Cooled Tropolone. Vibrational Assignment for the \ildeA1B2–\ildeX1A1 Transition

Infrared photodissociation spectra of [aniline−(H2O)n]+ (n = 1−8) are measured in the 2700−3800 cm-1 region. The spectra are interpreted with the aid of density functional theory calculations. The n = 1 ion has an N−H···O hydrogen bond. The spectrum of the n = 2 ion demonstrates a large perturbation to both of the NH oscillators, indicating the 1−1 structure where each NH bond is bound to a water molecule. For the n = 3 ion, the calculated spectrum of the 2−1 branched structure coincides well with the observed one. For the n = 4 ion, there exist three strong bands at 2960, 3100, and 3430 cm-1, as well as a very weak one at 3550 cm-1. The observed spectrum in the 3600−3800 cm-1 region is decomposed into four bands centered at 3640, 3698, 3710, and 3734 cm-1. The 2−2 branched isomer is responsible for all the features except the 3550 and 3710 cm-1 bands. These two bands are due to another isomer with a five-membered ring. An infrared band characteristic of the n = 5 ion appears at 3684 cm-1, which is not se...

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Infrared photodissociation spectroscopy of [Aniline-(Water)n]+ (n = 1-8): Structural change from branched and cyclic to proton-transferred forms

The S1–S0 fluorescence excitation and dispersed fluorescence spectra have been measured for jet‐cooled 5‐bromotropolone (5BTR‐h), 5‐chlorotropolone (5CTR‐h), and their OD derivatives in order to investigate substituent effects on proton tunneling. Both the 0++ and 0−− transitions were identified in the fluorescence spectra of these molecules. The tunneling doublet splittings in the electronic origin band of 5BTR‐h (16 cm−1) decreased by 4 cm−1, whereas that of 5CTR‐h (23 cm−1) increased by 3 cm−1 as compared with tropolone (TRN‐h). Relatively small deviation in the tunneling separations for these molecules from that for tropolone is ascribed to conjugation in the S1 state. An electron‐withdrawing character of chlorine and bromine atoms is almost canceled by a conjugative electron‐releasing effect.

Hiroshi Sekiya

Papers

Picosecond Time-Resolved Stokes and Anti-Stokes Raman Studies on the Photochromic Reactions of Diarylethene Derivatives

The Electronic Spectra of Jet-Cooled Tropolone. Vibrational Assignment for the \ildeA1B2–\ildeX1A1 Transition

Infrared photodissociation spectroscopy of [Aniline-(Water)n]+ (n = 1-8): Structural change from branched and cyclic to proton-transferred forms

Electronic spectra of jet‐cooled 5‐bromotropolone and 5‐chlorotropolone. Influence of symmetrical substitution on proton tunneling in the S1 state

Excited-state double-proton transfer in the (3-methyl-7-azaindole)-(7-azaindole) hetero-dimer in the gas phase