Does Inactive Alkyl Chain Enhance Triplet–Triplet Annihilation of 9,10-Diphenylanthracene Derivatives?

It has been hypothesized that alkyl chains are inactive for electron transport processes through the chains. However, our theoretical study unveiled that loop-like alkyl chains can accelerate the electron transfer of triplet–triplet annihilation (TTA) through overlap of the pseudo π-orbital of the alkyl chain. The TTA reaction time τ (the inverse of the TTA rate) of the dimer models of 9,10-diphenylanthracene (DPA) or the alkyl-strapped derivatives (C<i>n</i>-sDPAs) in a solution was calculated by the sequential charge transfer (SCT) processes of TTA with the Marcus theory. The τ for the C<i>n</i>-sDPAs were much shorter compared to that of DPA even at long distances and at various mutual orientations of the dimers. These shortened τ were due to the large electron coupling matrix elements through the pseudo-π-orbital that was extended to the alkyl chains in the singly occupied orbitals. This finding supports the observed superior performance of TTA upconversion obtained with C<i>n</i>-sDPAs

π‑Expanded Dipyrrolonaphthyridinediones with Large Two-Photon Absorption Cross-Section Values

A synthetic entry to novel dyes based on the dipyrrolonaphthyridinedione core was developed via the Heck reaction. These weakly fluorescent compounds bearing double bond linkages between the core and the peripheral units absorbed strongly in the far-red/NIR region and possessed large values of two-photon absorption (TPA) cross-sections (up to 5180 GM). Additionally, analogous dyes bearing triple bond linkages were also efficient TPA materials with relatively large two-photon absorption cross-sections (up to 2840 GM) as well as two-photon brightness (up to 1450 GM). The centrosymmetric nature of both of these families of dyes is responsible for the location of the maxima of two-photon absorption being at much higher energy than the ones corresponding to the double wavelength of the lowest-energy one-photon absorption. Theoretical calculations clarified that the enhancement of the TPA by the peripheral substitutions arose through different mechanisms depending on either the electron-donating or electron-withdrawing ability of a given substituent to the ambipolar core. The change in the electron distribution of HOMO and HOMO–1 by the push–pull effect was found to govern the strength of the lowest-energy TPA-allowed transition. Importantly, compounds from both series possessed a beneficial ratio of σ₂/MW (1.6–9.8 GM/g)

Phosphorus(V) Tetraazaporphyrin with an Intense, Broad CT Band in the Near-IR Region

In phosphorus tetraazaporphyrins (PTAPs), the Q- and charge-transfer (CT) bands appear as a result of configuration interaction between their excited states. On the basis of this concept, a PTAP with an intense, broad CT band in the near-IR region has been rationally designed and realized by introducing eight diphenylaminophenyl (dPAP) groups. The order of the CT and Q-bands in ascending energy was supported by magnetic circular dichroism (MCD) spectroscopy and theoretical calculations. An intense two-photon absorption was also found in the deep near-IR region

Synthesis and Functionalization of a 1,4-Bis(trimethylsilyl)tetrasila-1,3-diene through the Selective Cleavage of Si(sp²)–Si(sp³) Bonds under Mild Reaction Conditions

Although the oxidative coupling of disilenides, i.e., the disilicon analogues of vinyl anions, represents a promising route to extend the conjugation between SiSi double bonds, previously reported synthetic routes to disilenides involve strongly reducing conditions. Herein, we report a novel synthetic route to disilenides from stable disilenes via the selective cleavage of Si­(sp²)–Si­(sp³) bonds under milder reaction conditions. Using this method, a 1,4-bis­(trimethylsilyl)­tetrasila-1,3-diene (<b>5</b>) was synthesized from the corresponding silyl-substituted disilene. Moreover, Et₃Si-substituted tetrasila-1,3-diene <b>7</b> was synthesized via tetrasila-1,3-dien-1-ide <b>6</b>, which is the first example of a functionalized tetrasila-1,3-diene

Efficient Cycloreversion Reaction of a Diarylethene Derivative in Higher Excited States Attained by Off-Resonant Simultaneous Two-Photon Absorption

Off-resonant excitation of the closed-ring isomer of a photochromic diarylethene derivative at 730 nm induced the efficient cycloreversion reaction with a yield of ∼20%, while the reaction yield was only 2% under one-photon excitation at 365 nm. Excitation wavelength dependence of the one-photon cycloreversion reaction yield under steady-state irradiation in a wide wavelength range showed that the specific electronic state leading to the large cycloreversion reaction yield, which is originally forbidden in the optical transition but partially allowed owing to the low symmetry of the molecule, is spectrally overlapped with the electronic state accessible by the allowed one-photon optical transition in the UV region. Femtosecond transient absorption spectroscopy also revealed that the off-resonant two-photon excitation preferentially pumped the molecule into the specific state, leading to the 10-fold enhancement of the cycloreversion reaction

Singlet Diradical Character from Experiment

Understanding the electronic structure of the singlet diradical state tackles the fundamentals of the chemical bond itself. The singlet diradical character is a key factor, which determines the chemical reactivity, the reaction products, as well as the chemical/physical (electronic, optical and magnetic) properties, although this quantity is defined in a purely theoretical manner. In this Letter, on the basis of the valence configuration interaction scheme, we present an explicit connection between the singlet diradical character and measured quantities obtained from one- and two-photon absorption spectra as well as from phosphorescence and electron spin resonance peaks. This enables us to estimate the singlet diradical character experimentally

Fine Spatiotemporal Control of Nitric Oxide Release by Infrared Pulse-Laser Irradiation of a Photolabile Donor

Two-photon-excitation release of nitric oxide (NO) from our recently synthesized photolabile NO donor, Flu-DNB, was confirmed to allow fine spatial and temporal control of NO release at the subcellular level <i>in vitro</i>. We then evaluated <i>in vivo</i> applications. Femtosecond near-infrared pulse laser irradiation of predefined regions of interest in living mouse brain treated with Flu-DNB induced NO-release-dependent, transient vasodilation specifically at the irradiated site. Photoirradiation in the absence of Flu-DNB had no effect. Further, NO release from Flu-DNB by pulse laser irradiation was shown to cause chemoattraction of microglial processes to the irradiated area in living mouse brain. To our knowledge, this is the first demonstration of induction of biological responses <i>in vitro</i> and <i>in vivo</i> by means of precisely controlled, two-photon-mediated release of NO

Fine Spatiotemporal Control of Nitric Oxide Release by Infrared Pulse-Laser Irradiation of a Photolabile Donor

Two-photon-excitation release of nitric oxide (NO) from our recently synthesized photolabile NO donor, Flu-DNB, was confirmed to allow fine spatial and temporal control of NO release at the subcellular level <i>in vitro</i>. We then evaluated <i>in vivo</i> applications. Femtosecond near-infrared pulse laser irradiation of predefined regions of interest in living mouse brain treated with Flu-DNB induced NO-release-dependent, transient vasodilation specifically at the irradiated site. Photoirradiation in the absence of Flu-DNB had no effect. Further, NO release from Flu-DNB by pulse laser irradiation was shown to cause chemoattraction of microglial processes to the irradiated area in living mouse brain. To our knowledge, this is the first demonstration of induction of biological responses <i>in vitro</i> and <i>in vivo</i> by means of precisely controlled, two-photon-mediated release of NO

Fine Spatiotemporal Control of Nitric Oxide Release by Infrared Pulse-Laser Irradiation of a Photolabile Donor

Two-photon-excitation release of nitric oxide (NO) from our recently synthesized photolabile NO donor, Flu-DNB, was confirmed to allow fine spatial and temporal control of NO release at the subcellular level <i>in vitro</i>. We then evaluated <i>in vivo</i> applications. Femtosecond near-infrared pulse laser irradiation of predefined regions of interest in living mouse brain treated with Flu-DNB induced NO-release-dependent, transient vasodilation specifically at the irradiated site. Photoirradiation in the absence of Flu-DNB had no effect. Further, NO release from Flu-DNB by pulse laser irradiation was shown to cause chemoattraction of microglial processes to the irradiated area in living mouse brain. To our knowledge, this is the first demonstration of induction of biological responses <i>in vitro</i> and <i>in vivo</i> by means of precisely controlled, two-photon-mediated release of NO

Epidendrum proliferum

The characteristics of the edge state, which is a peculiar magnetic state in zigzag-edged graphene nanoribbons (ZGNRs) that originates from electron–electron correlation in an edge-localized π-state, are investigated by preparing and characterizing quarteranthene molecules. The molecular geometry that was determined from the X-ray analysis is consistent with a zigzag-edge-localized structure of unpaired electrons. The localized electrons are responsible for the peculiar magnetic (room-temperature ferromagnetic correlation), optical (the lowest-lying doubly excited state), and chemical (peroxide bond formation) behaviors. On the basis of these distinguishing properties and a careful consideration of the valence bonding, insight into the edge state of ZGNRs can be gained