Experimental evidence of the S state and fluorescence emission from the intramolecular charge transfer states in fucoxanthin.

Fucoxanthin is a typical carotenoid that absorbs light in the blue region of the visible spectrum, and its detailed electronic structures remain to be clarified. It is well known that carotenoids harvest energy from sunlight and transfer it to chlorophylls (Chls) and/or bacteriochlorophylls (BChls) through its excited states as the intermediate states; however, some excited states still need evidence to be definitely confirmed. Through steady-state fluorescence emission spectroscopy and femtosecond time-resolved fluorescence up-conversion technique, we provide new evidence for the identification of the excited S state in fucoxanthin, a representative of carotenoids.

Origin of Intersystem Crossing in Red-Light Absorbing Bodipy Derivatives: Time-Resolved Transient Optical and Electron Paramagnetic Resonance Spectral Studies with Twisted and Planar Compounds.

We studied the intersystem crossing (ISC) property of red-light absorbing heavy atom-free dihydronaphtho[]-fused Bodipy derivatives (with phenyl group attached at the lower rim via ethylene bridge, taking constrained geometry, i.e., and the half-oxidized product ) and dispiroflourene[]-fused Bodipy () that have a twisted π-conjugated framework.

Charge Transfer and Intersystem Crossing in Compact Naphthalenediimide-Phenothiazine Triads: Synthesis and Study of the Photophysical Property with Transient Optical and Electron Paramagnetic Resonance Spectroscopic Methods.

In order to obtain a long-lived charge separation (CS) state in compact electron donor-acceptor molecular systems, we prepared a series of naphthalenediimide (NDI)-phenothiazine (PTZ) triads, with phenylene as the linker between the donor and acceptor. Conformation restriction is imposed to control the mutual orientation of the NDI and PTZ units by attaching methyl groups on the phenylene linker to tune the electronic coupling between the donor and the acceptor. Moreover, the PTZ moiety was oxidized to sulfoxide to tune the ordering of the CS state and the LE state (LE: locally excited state).

Photocatalytic Metal Hydride Hydrogen Atom Transfer Mediated Allene Functionalization by Cobalt and Titanium Dual Catalysis.

Catalytic metal hydride hydrogen atom transfer (MHAT) reactions have proven to be a powerful method for alkene functionalization. This work reports the discovery of Co-porphines as highly efficient MHAT catalysts with a loading of only 0.01 mol % for unprecedented chemoselective allene functionalization under photoirradiation.

Plenty of Room on the Top: Pathways and Spectroscopic Signatures of Singlet Fission from Upper Singlet States.

We investigate dynamic signatures of the singlet fission (SF) process triggered by the excitation of a molecular system to an upper singlet state S ( > 1) and develop a computational methodology for the simulation of nonlinear spectroscopic signals revealing the S → TT SF in real time. We demonstrate that SF can proceed directly from the upper state S, bypassing the lowest excited state, S. We determine the main S → TT reaction pathways and show by computer simulation and spectroscopic measurements that the S-initiated SF can be faster and more efficient than the traditionally studied S → TT SF.

Singlet Fission, Polaron Generation and Intersystem Crossing in Hexaphenyl Film.

The ultrafast dynamics of triplet excitons and polarons in hexaphenyl film was investigated by time-resolved fluorescence and femtosecond transient absorption techniques under various excitation photon energies. Two distinct pathways of triplet formation were clearly observed. Long-lived triplet states are populated within 4.

Atomically Dispersed Indium-Copper Dual-Metal Active Sites Promoting C-C Coupling for CO Photoreduction to Ethanol.

Photoreduction of CO to C solar fuel is a promising carbon-neutral technology for renewable energy. This strategy is challenged by its low productivity due to low efficiency in multielectron utilization and slow C-C coupling kinetics. This work reports a dual-metal photocatalyst consisting of atomically dispersed indium and copper anchored on polymeric carbon nitride (InCu/PCN), on which the photoreduction of CO delivered an excellent ethanol production rate of 28.

Radical-Enhanced Intersystem Crossing in Perylene-Oxoverdazyl Radical Dyads.

Attaching stable radicals to organic chromophores is an effective method to enhance the intersystem crossing (ISC) of the chromophores. Herein we prepared perylene-oxoverdazyl dyads either by directly connecting the two units or using an intervening phenyl spacer. We investigated the effect of the radical on the photophysical properties of perylene and observed strong fluorescence quenching due to radical enhanced ISC (REISC).

Plasmonic Active "Hot Spots"-Confined Photocatalytic CO Reduction with High Selectivity for CH Production.

Plasmonic nanostructures have tremendous potential to be applied in photocatalytic CO reduction, since their localized surface plasmon resonance can collect low-energy-photons to derive energetic "hot electrons" for reducing the CO activation-barrier. However, the hot electron-driven CO reduction is usually limited by poor efficiency and low selectivity for producing kinetically unfavorable hydrocarbons. Here, a new idea of plasmonic active "hot spot"-confined photocatalysis is proposed to overcome this drawback.

Trap-free exciton dynamics in monolayer WS oleic acid passivation.

Two-dimensional transition metal dichalcogenides have attracted a great deal of attention in the past few decades owing to their attractive optoelectronic properties. However, their widespread utility in photonic devices and components is still limited owing to their weak photoluminescence. While various treating methods are in place to improve the photoluminescence yield, the impact of these treatments on the excited state (especially exciton) dynamics in these two-dimensional materials remains ill defined.

Toward efficient photochemistry from upper excited electronic states: Detection of long S lifetime of perylene.

A long 0.9 ps lifetime of the upper excited singlet state in perylene is resolved by femtosecond pump-probe measurements under ultraviolet (4.96 eV) excitation and further validated by theoretical simulations of transient absorption kinetics.

Switching Pathways of Triplet State Formation by Twisted Intramolecular Charge Transfer.

With the aim of constructing efficient photoelectric organic materials, a pyrido[3,2-]quinoline derivative named LA17b has been synthesized, and its photodynamic relaxation processes in solvents and films were studied by time-resolved fluorescence and femtosecond transient absorption techniques. The steady-state fluorescence spectra show pronounced red-shift with the increase of the solvent polarity as well as in binary solvent hexane/ethanol by increasing ethanol concentration. However, the strong red-shift does not lead to quenching of the fluorescence.

Bodipy-Containing Porous Microcapsules for Flow Heterogeneous Photocatalysis.

Photocatalysis is a facile strategy for complex chemical transformations. Heterogeneous photocatalysis, especially in the flow system, has attracted much attention as it avoids the separation of catalysts. Herein, a kind of a Bodipy-containing porous microcapsule heterogeneous photocatalyst was rationally constructed with modulation on a multiscale.

Does Twisted π-Conjugation Framework Always Induce Efficient Intersystem Crossing? A Case Study with Benzo[]- and []Phenanthrene-Fused BODIPY Derivatives and Identification of a Dark State.

The photophysical properties, especially the intersystem crossing (ISC) of two heavy-atom-free BODIPY derivatives with twisted π-conjugated frameworks (benzo[]-fused BODIPY, ; and []phenanthrene-fused BODIPY, ), are studied with steady-state and time-resolved optical and electron paramagnetic resonance (TREPR) spectroscopic methods as well as with ADC(2) theoretical investigations. Interestingly, has a planar π-conjugation framework, but it displays UV-vis absorption (ε = 3.8 × 10 M cm at 569 nm) and fluorescence (Φ < 0.

Ultrafast spectroscopy reveals singlet fission, ionization and excimer formation in perylene film.

Singlet exciton fission (SF) is a spin-allowed process whereby two triplet excitons are created from one singlet exciton. This phenomenon can offset UV photon energy losses and enhance the overall efficiency in photovoltaic devices. For this purpose, it requires photostable commercially available SF materials.

Singlet fission from upper excited singlet states and polaron formation in rubrene film.

Femtosecond fluorescence up-conversion and transient absorption pump-probe setups are applied to study the relaxation dynamics of the lower and upper excited singlet electronic states in easy-to-make rubrene films. Upon 250 nm (4.96 eV) excitation, singlet fission was observed directly from S state bypassing S state within 30 fs breaking the classical Kasha rule.

Spin-Orbit Charge-Transfer Intersystem Crossing in Anthracene-Perylenebisimide Compact Electron Donor-Acceptor Dyads and Triads and Photochemical Dianion Formation.

Perylenebisimide (PBI)-anthracene (AN) donor-acceptor dyads/triad were prepared to investigate spin-orbit charge-transfer intersystem crossing (SOCT-ISC). Molecular conformation was controlled by connecting PBI units to the 2- or 9-position of the AN moiety. Steady-state, time-resolved transient absorption and emission spectroscopy revealed that chromophore orientation, electronic coupling, and dihedral angle between donor and acceptor exert a significant effect on the photophysical property.

N^N Pt(II) Bisacetylide Complexes with Oxoverdazyl Radical Ligands: Preparation, Photophysical Properties, and Magnetic Exchange Interaction between the Two Radical Ligands.

To study the effect of a stable radical on the photophysical properties of a phosphorescent Pt(II) coordination framework and the intramolecular magnetic interaction between radical ligands in the N^N Pt(II) bisacetylide complexes, we prepared a series of N^N Pt(II) bis(acetylide) complexes with oxoverdazyl radical acetylide ligands. The linker between the Pt(II) center and the spin carrier was systematically varied, to probe the effect on the sign and magnitude of the spin exchange interactions between the radical ligands and photophysical properties. The complexes were studied with steady-state and femtosecond/nanosecond transient absorption spectroscopy, continuous-wave electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) computations.

Upper Excited State Photophysics of Malachite Green in Solution and Films.

Relaxation pathways of upper excited electronic states of malachite green (MG) in ethanol and in films are studied by steady-state and time-resolved spectroscopic techniques. In contrast to ethanol, where MG emits weak short-lived spectrally well separated S and S fluorescence with the lifetimes ∼0.3 and ∼0.

Direct Observation of Long-Lived Upper Excited Triplet States and Intersystem Crossing in Anthracene-Containing Pt Complexes.

Exceptionally long-lived T states (7 ns) were observed with the N^N Pt bisacetylide complex () and -bis(phosphine) Pt bisacetylide complexes (, ) containing anthryl acetylide ligands. For , fluorescence of the anthryl moiety (An) was quenched and phosphorescence was observed. Under 350 nm excitation, the upper long-lived triplet state T (An) was populated via ultrafast intersystem crossing (ISC) of S (An) → T (An) (within 0.

Singlet Fission from Upper Excited Electronic States of Cofacial Perylene Dimer.

Singlet fission directly from the upper excited vibrational and electronic states of cofacial perylene dimers, bypassing the relaxed state S, was detected within 50 fs. This process competes well with vibrational cooling in S (4.7-7.

Nitroreductase-Activatable Theranostic Molecules with High PDT Efficiency under Mild Hypoxia Based on a TADF Fluorescein Derivative.

High specificity detection and site-specific therapy are still the main challenges for theranostic anticancer prodrugs. In this work, we reported two smart activatable theranostic molecules based on a thermally activated delayed fluorescence fluorescein derivative. Nitroreductase induced by a mild hypoxia microenvironment of a solid tumor was used to activate the fluorescence and photodynamic therapy (PDT) efficiency by employing the intramolecular photoinduced electron transfer mechanism.

Anthracene-Naphthalenediimide Compact Electron Donor/Acceptor Dyads: Electronic Coupling, Electron Transfer, and Intersystem Crossing.

We attached different electron donors of phenyl, anthryl, and alkylamino moieties, to electron acceptor naphthalenediimide (NDI) to construct compact electron donor/acceptor dyads. The purpose is to study the effect of electron coupling (the magnitude is the matrix element, V) on the photophysical properties of UV-vis absorption, fluorescence emission, especially spin-orbit charge transfer intersystem crossing. We found that the magnitude of V depends on the electron donating strength of the aryl moieties ( V = 0.