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The in situ generation of active photoredox organic catalysts upon anion‐binding co‐catalysis by making use of the ionic nature of common photosensitizers is reported. Hence, the merge of anion‐binding and photocatalysis permitted the modulation of the photocatalytic activity of simple acridinium halide salts, building an effective anion‐binding – photoredox ion pair complex able to promote a variety of visible light driven transformations, such as anti‐Markovnikov addition to olefins, Diels‐Alder and the desilylative C−C bond forming reactions. Anion‐binding studies, together with steady‐state and time‐resolved spectroscopy analysis, supported the postulated ion pair formation between the thiourea hydrogen‐bond donor organocatalyst and the acridinium salt, which proved essential for unlocking the photocatalytic activity of the photosensitizer. [ABSTRACT FROM AUTHOR]

The ability of light to change the properties of light‐responsive polymers opens avenues for targeted release of cargo with a high degree of spatial and temporal control. Recently, we established photoacid polymers as light‐switchable macromolecular amphiphiles. In these systems, light‐induced excited‐state proton transfer (ESPT) causes changes in amphilicity. However, as the intermolecular process itself critically depends on the local environment of the photoacid unit within the polymer, the overall amphiphilicity directly influences ESPT. Thus, understanding the impact of the local environment on the photophysics of photoacidic side chains is key to material design. In this contribution we address both thermodynamic and kinetic aspects of ESPT in oxazoline‐based amphiphilic polymers with pyrenol‐based photoacid side chains. We will compare the effect of polymer design, i. e. statistical and block arrangements, i. e. in poly[(2‐ethyl‐2‐oxazoline)‐co‐(1‐(6/8‐hydroxyperene)sulphonylaziridine)] and poly(2‐ethyl‐2‐oxazoline)‐block‐poly[(2‐ethyl‐2‐oxazoline)‐co‐(2‐(3‐(6‐hydroxypyrene)sulphonamide)propyl‐2‐oxazoline), on the intermolecular proton transfer reaction by combining steady‐state and time‐resolved absorption and emission spectroscopy. ESPT appears more prominent in the statistical copolymer compared to a block copolymer with overall similar pyrenol loading. We hypothesize that the difference is due to different local chain arrangements adopted by the polymers in the two cases. [ABSTRACT FROM AUTHOR]

Studying the direct effects of DNA irradiation is essential for understanding the impact of radiation on biological systems. Gas‐phase interactions are especially well suited to uncover the molecular mechanisms underlying these direct effects. Only relatively recently, isolated DNA oligonucleotides were irradiated by ionizing particles such as VUV or X‐ray photons or ion beams, and ionic products were analyzed by mass spectrometry. This article provides a comprehensive review of primarily experimental investigations in this field over the past decade, emphasizing the description of processes such as ionization, fragmentation, charge and hydrogen transfer triggered by photoabsorption or ion collision, and the recent progress made thanks to specific atomic photoabsorption. Then, we outline ongoing experimental developments notably involving ion‐mobility spectrometry, crossed beams or time‐resolved measurements. The discussion extends to potential research directions for the future. [ABSTRACT FROM AUTHOR]

A close mimic of P680 and the TyrosineZ‐Histidine190 pair in photosystem II (PS II) has been synthesized using a ruthenium chromophore and imidazole‐phenol ligands. The intramolecular oxidation of the ligands by the photoproduced Ru(III) species is characterized by a small driving force, very similar to PS II where the complexity of kinetics was attributed to the reversibility of electron transfer steps. Laser flash photolysis revealed biphasic kinetics for ligand oxidation. The fast phase (τ<50 ns) corresponds to partial oxidation of the imidazole‐phenol ligand, proton transfer within the hydrogen bond, and formation of a neutral phenoxyl radical. The slow phase (5–9 μs) corresponds to full oxidation of the ligand which is kinetically controlled by deprotonation of the distant 1‐nitrogen of the imidazolium. These results show that imidazole with its two protonatable sites plays a special role as a proton relay in a 'proton domino' reaction. [ABSTRACT FROM AUTHOR]

Bodipy (BDP)‐perylenebisimide (PBI) donor–acceptor dyads/triad were prepared to study the spin–orbit charge‐transfer intersystem crossing (SOCT‐ISC). For BDP‐PBI‐3, in which BDP was attached at the imide position of PBI, higher singlet oxygen quantum yield (ΦΔ=85 %) was observed than the bay‐substituted derivative BDP‐PBI‐1 (ΦΔ=30 %). Femtosecond transient absorption spectra indicate slow Förster resonance energy transfer (FRET; 40.4 ps) and charge separation (CS; 1.55 ns) in BDP‐PBI‐3, while for BDP‐PBI‐1, CS takes 2.8 ps. For triad BDP‐PBI‐2, ultrafast FRET (149 fs) and CS (4.7 ps) process were observed, the subsequent charge recombination (CR) takes 5.8 ns and long‐lived 3PBI* (179.8 μs) state is populated. Nanosecond transient absorption spectra of BDP‐PBI‐3 show that the CR gives upper triplet excited state (3BDP*) and subsequently, via a slow intramolecular triplet energy transfer (14.5 μs), the 3PBI* state is finally populated, indicating that upper triplet state is involved in SOCT‐ISC. Time‐resolved electron paramagnetic resonance spectroscopy revealed that both radical pair ISC (RP ISC) and SOCT‐ISC contribute to the ISC. A rare electron spin polarization of (e, e, e, e, e, e) was observed for the triplet state formed via the RP ISC mechanism, due to the S−T+1/T0 states mixing. [ABSTRACT FROM AUTHOR]

The tetrahedral shape‐persistent molecule 14+, containing four identical pyridyl pyridinium units connected via a sp3 hybridized carbon atom, has been investigated in detail by means of steady‐state and time resolved spectroscopy. Remarkable photophysical properties are observed, particularly in comparison with protonated and methylated analogues (1H48+, 1Me48+), which exhibit substantially shorter excited state lifetimes and lower emission quantum yields. Theoretical studies have rationalized the behavior of the tetrameric molecules relative to the monomers, with DFT and TD‐DFT calculations corroborating steady‐state (absorption and emission) and transient absorption spectra. The behavior of the monomeric compounds (each consisting in one of the four identical subunits of the tetramers, i. e. 2+, 2H2+ and 2Me2+) considerably differs from that of the tetramers, indicating a strong electronic interaction between the subunits in the tetrameric species, likely promoted by the homoconjugation through the connecting sp3 C atom. 2+ is characterized by a peculiar S1‐S2 excited state inversion, whereas the short‐lived emitting S1 state of 2H2+ and 2Me2+ exhibits a partial charge‐transfer character, as substantiated by spectro‐electrochemical studies. Among the six investigated systems, only 14+ is a sizeable luminophore (Φem=0.15), which is related to the peculiar features of its singlet state. [ABSTRACT FROM AUTHOR]

Azidoporphinatoiron(III) ([1]) is an archetypal model complex for the photochemical generation of nitridoiron(V) complexes via cleavage of dinitrogen. So far, this process has only been studied with continuous irradiation in thin films under cryogenic conditions or in frozen solutions. In addition, the photooxidation from iron(III) to iron(V) competes with photoreduction to iron(II) via cleavage of an azidyl radical. The quantum yields of both pathways remained hitherto undisclosed. Here, we investigated the photolysis of this model complex in room temperature liquid solution using stationary and time‐resolved infrared spectroscopy. The two reaction pathways are unambiguously identified in quenching studies and their quantum yields are accurately determined. Nitridoporphinatoiron(V) ([2]) exhibits N‐atom‐2‐electron‐transfer reactivity toward tert‐butyl isonitrile and forms a carbodiimido species. In the presence of tert‐butyl isonitrile, the two products of the photoreduction pathway react to cationic diisonitriloporphinatoiron(III) and azide anions, which in turn combine to reform [1] and the quencher. [ABSTRACT FROM AUTHOR]

Fluorescent probes based on photoinduced electron transfer (PET) quenching of long lifetime triangulenium fluorophores have found multiple applications. For such probes a successful design relies on the right balance between the rate of PET quenching and fluorescence. In a series of ADOTA (A) and DAOTA (D) triangulenium fluorophores appended with aniline‐like quencher moieties, we have investigated the rate of quenching and its relation to thermodynamic driving force, distance, and conjugation within the quencher moiety. Three different quenchers, a short (1), a long (2), and a long twisted (3), 4‐aminophenyl, 4'‐aminobiphenyl, and 2,2'‐dimethyl‐4'‐aminobiphenyl, respectively were investigated. Steady‐state spectroscopy and electrochemistry confirms that the quencher moieties are electronically decoupled from the dyes and have similar oxidation potentials and thus driving force for PET quenching, irrespectively of their different length and conjugation. Time‐resolved fluorescence measurement was used to measure the fast PET quenching, with rate constant kPET ranging from >4×1011 to 2×109 s−1. Interestingly, PET quenching is equally efficient/fast from 1 and 2, even with increase in distance between the donor and the acceptor. However, when twisting the biphenyl in 3, a 20‐fold decrease in quenching is found. Even with this decrease in kPET, the quenching in 3 A/D is still highly efficient, with nearly 99 % quenching. The study show that long lifetime fluorophores can be efficiently switched even by relatively slow PET processes and that PET quencher moieties can be removed far from the fluorophore if conjugated linkers are applied. [ABSTRACT FROM AUTHOR]

Metal‐free organic emitters that display solution‐phase room temperature phosphorescence (sRTP) remain exceedingly rare. Here, we investigate the structural and photophysical properties that support sRTP by comparing a recently reported sRTP compound (BTaz−Th−PXZ) to two novel analogous materials, replacing the donor group by either acridine or phenothiazine. The emissive triplet excited state remains fixed in all three cases, while the emissive charge‐transfer singlet states (and the calculated paired charge‐transfer T2 state) vary with the donor unit. While all three materials show dominant RTP in film, in solution different singlet‐triplet and triplet‐triplet energy gaps give rise to triplet‐triplet annihilation followed by weak sRTP for the new compounds, compared to dominant sRTP throughout for the original PXZ material. Engineering both the sRTP state and higher charge‐transfer states therefore emerges as a crucial element in designing emitters capable of sRTP. [ABSTRACT FROM AUTHOR]

Stimuli responsive luminescent materials possessing room temperature phosphorescence (RTP) are extremely desirable for various applications. The here investigated derivative of cyclic triimidazole (TT) functionalized with carbazole (Cz), namely TT‐Ph‐Cz, belongs to this class. TT‐Ph‐Cz possesses high conformational freedom resulting in rigidochromic and multi‐stimuli responsive emissive behavior. It has been isolated as MeOH‐solvated and de‐solvated forms characterized by distinctive emissive features. In particular, the solvated form, in which hydrogen bonds with MeOH inhibit competitive non‐radiative deactivation channels, possesses a higher quantum yield associated with a strong phosphorescence contribution which is preserved in DMSO/water solutions. [ABSTRACT FROM AUTHOR]

The photophysical processes involved in the electron donor-acceptor thermally activated delayed fluorescence (TADF) emitters are complicated and controversial. The recent consensus is that at least three states are involved, i. e. the singlet charge transfer state (¹CT), the triplet localized excited state (³LE) and the triplet CT state (³CT). It is clear the very often used steady state and time-resolved luminescence spectroscopic methods are unable to present direct evidence for the dark states, i. e. the ³LE and ³CT states, as well as the interconversion of these states. Concerning this aspect, the femtosecond-nanosecond transient absorption spectroscopic methods are in particular interests. Both the emissive state and the dark state can be detected in these spectra, and interconversion of the states involved in TADF process can be also revealed. This review article focuses on the recent development of using the transient absorption spectra to study the photophysics of the TADF emitters. [ABSTRACT FROM AUTHOR]

Two four-coordinate organoboron N,C-chelate complexes with different functional terminals on the PEG chains are studied with respect to their photophysical properties within human MCF-7 cells. Their excited-state properties are characterized by time-resolved pump-probe spectroscopy and fluorescence lifetime microscopy. The excited-state relaxation dynamics of the two complexes are similar when studied in DMSO. Aggregation of the complexes with the carboxylate terminal group is observed in water. When studying the light-driven excited-state dynamics of both complexes in cellulo, i. e., after being taken up into human MCF-7 cells, both complexes show different features depending on the nature of the anchoring PEG chains. The lifetime of a characteristic intramolecular charge-transfer state is significantly shorter when studied in cellulo (360±170 ps) as compared to in DMSO (-960 ps) at 600 nm for the complexes with an amino group. However, the kinetics of the complexes with the carboxylate group are in line with those recorded in DMSO. On the other hand, the lifetimes of the fluorescent state are almost identical for both complexes in cellulo. These findings underline the importance to evaluate the excited-state properties of fluorophores in a complex biological environment in order to fully account for intra- and intermolecular effects governing the light-induced processes in functional dyes. [ABSTRACT FROM AUTHOR]

Emitters for organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) require small singlet (S1)‐triplet (T1) energy gaps as well as fast intersystem crossing (ISC) transitions. These transitions can be mediated by vibronic mixing with higher excited states Sn and Tn (n=2, 3, 4, ...). For a prototypical TADF emitter consisting of a triarylamine and a dicyanobenzene moiety (TAA‐DCN) it is shown that these higher states can be located energetically by time‐resolved near‐infrared (NIR) spectroscopy. [ABSTRACT FROM AUTHOR]

In this paper, the photophysical behavior of four panchromatically absorbing, homoleptic bis(4H‐imidazolato)CuI complexes, with a systematic variation in the electron‐withdrawing properties of the imidazolate ligand, were studied by wavelength‐dependent time‐resolved femtosecond transient absorption spectroscopy. Excitation at 400, 480, and 630 nm populates metal‐to‐ligand charge transfer, intraligand charge transfer, and mixed‐character singlet states. The pump wavelength‐dependent transient absorption data were analyzed by a recently established 2D correlation approach. Data analysis revealed that all excitation conditions yield similar excited‐state dynamics. Key to the excited‐state relaxation is fast, sub‐picosecond pseudo‐Jahn‐Teller distortion, which is accompanied by the relocalization of electron density onto a single ligand from the initially delocalized state at Franck‐Condon geometry. Subsequent intersystem crossing to the triplet manifold is followed by a sub‐100 ps decay to the ground state. The fast, nonradiative decay is rationalized by the low triplet‐state energy as found by DFT calculations, which suggest perspective treatment at the strong coupling limit of the energy gap law. [ABSTRACT FROM AUTHOR]

Catalyst recovery is an integral part of photoredox catalysis. It is often solved by adding another component‐a sacrificial agent‐whose role is to convert the catalyst back into its original oxidation state. However, an additive may cause a side reaction thus decreasing the selectivity and overall efficiency. Herein, we present a novel approach towards chemoselective photooxidation reactions based on suitable solvent‐acetonitrile acting simultaneously as an electron acceptor for catalyst recovery, and on anaerobic conditions. This is allowed by the unique properties of the catalyst, 7,8‐dimethoxy‐3‐methyl‐5‐phenyl‐5‐deazaflavinium chloride existing in both strongly oxidizing and reducing forms, whose strength is increased by excitation with visible light. Usefulness of this system is demonstrated in chemoselective dehydrogenations of 4‐methoxy‐ and 4‐chlorobenzyl alcohols to aldehydes without over‐oxidation to benzoic acids achieving yields up to 70 %. 4‐Substituted 1‐phenylethanols were oxidized to ketones with yields 80–100 % and, moreover, with yields 31‐98 % in the presence of benzylic methyl group, diphenylmethane or thioanisole which are readily oxidized in the presence of oxygen but these were untouched with our system. Mechanistic studies based on UV‐Vis spectro‐electrochemistry, EPR and time‐resolved spectroscopy measurements showed that the process involving an electron release from an excited deazaflavin radical to acetonitrile under formation of solvated electron is crucial for the catalyst recovery. [ABSTRACT FROM AUTHOR]

The ambitious goal of artificial photosynthesis is to develop active systems that mimic nature and use light to split water into hydrogen and oxygen. Intramolecular design concepts are particularly promising. Herein, we firstly present an intramolecular photocatalyst integrating a perylene‐based light‐harvesting moiety and a catalytic rhodium center (RhIIIphenPer). The excited‐state dynamics were investigated by means of steady‐state and time‐resolved absorption and emission spectroscopy. The studies reveal that photoexcitation of RhIIIphenPer yields the formation of a charge‐separated intermediate, namely RhIIphenPer⋅+, that results in a catalytically active species in the presence of protons. [ABSTRACT FROM AUTHOR]

Increasing the metal‐to‐ligand charge transfer (MLCT) excited state lifetime of polypyridine iron(II) complexes can be achieved by lowering the ligand's π* orbital energy and by increasing the ligand field splitting. In the homo‐ and heteroleptic complexes [Fe(cpmp)2]2+ (12+) and [Fe(cpmp)(ddpd)]2+ (22+) with the tridentate ligands 6,2"‐carboxypyridyl‐2,2'‐methylamine‐pyridyl‐pyridine (cpmp) and N,N'‐dimethyl‐N,N'‐di‐pyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) two or one dipyridyl ketone moieties provide low energy π* acceptor orbitals. A good metal‐ligand orbital overlap to increase the ligand field splitting is achieved by optimizing the octahedricity through CO and NMe units between the coordinating pyridines which enable the formation of six‐membered chelate rings. The push‐pull ligand cpmp provides intra‐ligand and ligand‐to‐ligand charge transfer (ILCT, LL'CT) excited states in addition to MLCT excited states. Ground and excited state properties of 12+ and 22+ were accessed by X‐ray diffraction analyses, resonance Raman spectroscopy, (spectro)electrochemistry, EPR spectroscopy, X‐ray emission spectroscopy, static and time‐resolved IR and UV/Vis/NIR absorption spectroscopy as well as quantum chemical calculations. [ABSTRACT FROM AUTHOR]

The design of photoactive systems capable of storing and relaying multiple electrons is highly demanded in the field of artificial photosynthesis, where transformations of interest rely on multielectronic redox processes. The photophysical properties of the ruthenium photosensitizer [(bpy)2Ru(oxim‐dppqp)]2+ (Ru), storing two electrons coupled to two protons on the π‐extended oxim‐dppqp ligand under light‐driven conditions, are investigated by means of excitation wavelength‐dependent resonance Raman and transient absorption spectroscopies, in combination with time‐dependent density functional theory; the results are discussed in comparison to the parent [(bpy)2Ru(dppz)]2+ and [(bpy)2Ru(oxo‐dppqp)]2+ complexes. In addition, this study provides in‐depth insights on the impact of protonation or of accumulation of multiple reducing equivalents on the reactive excited states. [ABSTRACT FROM AUTHOR]

Inorganic red‐NIR emissive materials are particularly relevant in many fields like optoelectronic, bioimaging or solar cells. Benefiting from their emission in devices implies their integration in easy‐to‐handle materials like liquid crystals, whose long‐range ordering and self‐healing abilities could be exploited and influence emission. Herein, we present red‐NIR emissive hybrid materials obtained with phosphorescent octahedral molybdenum cluster anions electrostatically associated with amphiphilic guanidinium minidendrons. Polarized optical microscopy and X‐ray analysis show that while the minidendron chloride salts self‐organize into columnar phases, their association with the dianionic metal cluster leads to layered phases. Steady‐state and time‐resolved emission investigations demonstrate the influence of the minidendron alkyl chain length on the phosphorescence of the metal cluster core. [ABSTRACT FROM AUTHOR]

Multichromophoric systems based on a RuII polypyridine moiety containing an additional organic chromophore are of increasing interest with respect to different light‐driven applications. Here, we present the synthesis and detailed characterization of a novel RuII photosensitizer, namely [(tbbpy)2Ru((2‐(perylen‐3‐yl)‐1H‐imidazo[4,5‐f][1,10]‐phenanthrolline))](PF6)2RuipPer, that includes a merged perylene dye in the back of the ip ligand. This complex features two emissive excited states as well as a long‐lived (8 μs) dark state in acetonitrile solution. Compared to prototype [(bpy)3Ru]2+‐like complexes, a strongly altered absorption (ϵ=50.3×103 M−1 cm−1 at 467 nm) and emission behavior caused by the introduction of the perylene unit is found. A combination of spectro‐electrochemistry and time‐resolved spectroscopy was used to elucidate the nature of the excited states. Finally, this photosensitizer was successfully used for the efficient formation of reactive singlet oxygen. [ABSTRACT FROM AUTHOR]

Recent advances in sustainable optoelectronics including photovoltaics, light‐emitting diodes, transistors, and semiconductors have been enabled by π‐conjugated organic molecules. A fundamental understanding of light‐matter interactions involving these materials can be realized by time‐resolved electronic and vibrational spectroscopies. In this Minireview, the photoinduced mechanisms including charge/energy transfer, electronic (de)localization, and excited‐state proton transfer are correlated with functional properties encompassing optical absorption, fluorescence quantum yield, conductivity, and photostability. Four naturally derived molecules (xylindein, dimethylxylindein, alizarin, indigo) with ultrafast spectral insights showcase efficient energy dissipation involving H‐bonding networks and proton motions, which yield high photostability. Rational design principles derived from such investigations could increase the efficiency for light harvesting, triplet formation, and photosensitivity for improved and versatile optoelectronic performance. [ABSTRACT FROM AUTHOR]

Polyoxothiometalate ions (ThioPOM) are active hydrogen‐evolution reaction (HER) catalysts based on modular assembly built from electrophilic clusters {MoSx} and vacant polyoxotungstates. Herein, the dumbbell‐like anion [{(PW11O39)Mo3S4(H2O)3(OH)}2]8− exhibits very high light‐driven HER activity, while the active cores {Mo3S4} do not contain any exposed disulfido ligands, which were suspected to be the origin of the HER activity. Moreover, in the catalyst architecture, the two central {Mo3S4} cores are sandwiched by two {PW11O39}7− subunits that act as oxidant‐resistant protecting groups and behave as electron‐collecting units. A detailed photophysical study was carried out confirming the reductive quenching mechanism of the photosensitizer [Ir(ppy)2(dtbbpy)]+ by the sacrificial donor triethanolamine (TEOA) and highlighting the very high rate constant of the electron transfer from the reduced photosensitizer to the ThioPOM catalyst. Such results provide new insights into the field of molecular catalytic systems able to promote high HER activity. [ABSTRACT FROM AUTHOR]

Organic materials with multiple emissions tunable by external stimuli represent a great challenge. TTPyr, crystallizing in different polymorphs, shows a very rich photophyisics comprising excitation‐dependent fluorescence and phosphorescence at ambient conditions, and mechanochromic and thermochromic behavior. Transformation among the different species has been followed by thermal and X‐ray diffraction analyses and the emissive features interpreted through structural results and DFT/TDDFT calculations. Particularly intriguing is the polymorph TTPyr(HT), serendipitously obtained at high temperature but stable also at room temperature, whose non‐centrosymmetric structure guarantees an SHG efficiency 10 times higher than that of standard urea. Its crystal packing, where only the TT units are strongly rigidified by π‐π stacking interactions while the Pyr moieties possess partial conformational freedom, is responsible for the observed dual fluorescence. The potentialities of TTPyr for bioimaging have been successfully established. [ABSTRACT FROM AUTHOR]

Chemical and spectroscopic characterization of the mononuclear photosensitizers [(DPEPhos)Cu(I)(MPyrT)]0/+ (CuL, CuLH) and their dinuclear analogues (Cu2L', Cu2L'H2), backed by (TD)DFT and high‐level GW‐Bethe‐Salpeter equation calculations, exemplifies the complex influence of charge, nuclearity and structural flexibility on UV‐induced photophysical pathways. Ultrafast transient absorption and step‐scan FTIR spectroscopy reveal flattening distortion in the triplet state of CuLH as controlled by charge, which also appears to have a large impact on the symmetry of the long‐lived triplet states in Cu2L' and Cu2L'H2. Time‐resolved luminescence spectroscopy (solid state), supported by transient photodissociation spectroscopy (gas phase), confirm a lifetime of some tens of μs for the respective triplet states, as well as the energetics of thermally activated delayed luminescence, both being essential parameters for application of these materials based on earth‐abundant copper in photocatalysis and luminescent devices. [ABSTRACT FROM AUTHOR]

The synthesis of copper and zinc complexes of four variably substituted iminophosphonamide ligands is presented. While the copper complexes form ligand‐bridged dimers, the zinc compounds are monomeric. Due to different steric demand of the ligand the arrangement of the ligands within the dimeric complexes varies. Similar to the structurally related iminophosphonamide complexes of alkali metals and calcium, the steady‐state and time‐resolved photoluminescence (PL) of four of the seven compounds studied here as solids in a temperature range of 5–295 K can be described within the scheme of thermally activated delayed fluorescence (TADF). Accordingly, they exhibit bright blue‐green phosphorescence at low temperatures (<100 K), which turns into delayed fluorescence by increasing the temperature. However, unusually, the fluorescence is practically absent in two copper complexes which otherwise still conform to the TADF scheme. In these cases, the excited singlet states decay essentially non‐radiatively and their thermal population from the corresponding low‐lying triplet states efficiently quenches PL (phosphorescence). Three other copper and zinc complexes only exhibit prompt fluorescence, evidencing a wide variation of photophysical properties in this class of compounds. The excited states of the copper complex with especially pronounced phosphorescence quenching were also investigated by low‐temperature time‐resolved infrared spectroscopy and quantum chemical calculations. [ABSTRACT FROM AUTHOR]

A new base metal iron‐cobalt dyad has been obtained by connection between a heteroleptic tetra‐NHC iron(II) photosensitizer combining a 2,6‐bis[3‐(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]pyridine with 2,6‐bis(3‐methyl‐imidazol‐2‐ylidene)‐4,4′‐bipyridine ligand, and a cobaloxime catalyst. This novel iron(II)‐cobalt(III) assembly has been extensively characterized by ground‐ and excited‐state methods like X‐ray crystallography, X‐ray absorption spectroscopy, (spectro‐)electrochemistry, and steady‐state and time‐resolved optical absorption spectroscopy, with a particular focus on the stability of the molecular assembly in solution and determination of the excited‐state landscape. NMR and UV/Vis spectroscopy reveal dissociation of the dyad in acetonitrile at concentrations below 1 mM and high photostability. Transient absorption spectroscopy after excitation into the metal‐to‐ligand charge transfer absorption band suggests a relaxation cascade originating from hot singlet and triplet MLCT states, leading to the population of the 3MLCT state that exhibits the longest lifetime. Finally, decay into the ground state involves a 3MC state. Attachment of cobaloxime to the iron photosensitizer increases the 3MLCT lifetime at the iron centre. Together with the directing effect of the linker, this potentially makes the dyad more active in photocatalytic proton reduction experiments than the analogous two‐component system, consisting of the iron photosensitizer and Co(dmgH)2(py)Cl. This work thus sheds new light on the functionality of base metal dyads, which are important for more efficient and sustainable future proton reduction systems. [ABSTRACT FROM AUTHOR]

Enhancement of the luminescence efficiency of two new diazapentacenium salts (D1 and D2) of more than 55 for D1 and 22 times for D2) in poor solvents, acetonitrile and/or dichloromethane, was observed and rationalized as formation of emissive J‐aggregates. Both compounds displaying 4‐n‐decylphenyl substituents at the 7,14‐carbons and phenyl (D1) or 2,6‐difluorophenyl (D2) substituents at the quaternary nitrogen atoms in 5,12‐positions have been synthetized in a two‐step procedure involving a two‐fold Buchwald‐Hartwig‐type CN cross‐coupling and an electrophilic Friedel‐Crafts‐type cyclization. The optical properties of the dicationic diazapentacenium salts in various solvents and in thin films have been investigated by steady‐state and time‐resolved absorption and photoluminescence spectroscopies. In thin films and in good solvents, isolated molecules coexist with aggregates. Nonetheless, D1 is seven times more emissive than D2, reflecting a higher J‐aggregate contribution in the former. [ABSTRACT FROM AUTHOR]

The photochemical behaviour of selected aryl sulfonates and phosphates (ArOX) in polar and nonpolar media has been investigated by laser flash photolysis (LFP) experiments. Two main pathways have been identified, namely the photohomolysis of the ArO−X bond or the photoheterolysis of the Ar−OX bond depending on the nature of the leaving group (OX) and on the nature of the substituents on the aromatic ring. In nonpolar solvents the esters are quite photostable due to an efficient triplet deactivation. In polar solvents, the homolytic fragmentation of the ArO−S bond from the exited singlets was found in aryl sulfonates bearing moderately electron‐donating groups as well as electron‐withdrawing groups. In electron‐rich aryl phosphates and sulfonates photoheterolysis of the Ar−OP/Ar−OS bond took place as the exclusive pathway. [ABSTRACT FROM AUTHOR]

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. The dyad PBI‐9‐AN with orthogonal geometry shows weak ground‐state coupling and efficient intersystem crossing (ISC, ΦΔ=86 %) as compared with PBI‐2‐AN (ΦΔ=57 %), which has a more coplanar geometry. By nanosecond transient absorption spectroscopy, a long‐lived PBI localized triplet state was observed (τT=139 μs). Time‐resolved EPR spectroscopy demonstrated that the electron spin polarization pattern of the triplet state is sensitive to the geometry and number of AN units attached to PBI. Reversible and stepwise generation of near‐IR‐absorbing PBI radical anion (PBI−⋅) and dianion (PBI2−) was observed on photoexcitation in the presence of triethanolamine, and it was confirmed that selective photoexcitation at the near‐IR absorption bands of PBI.− is unable to produce PBI2−. [ABSTRACT FROM AUTHOR]

Ultrafast optical control of intramolecular charge flow was demonstrated, which paves the way for photocurrent modulation and switching with a highly wavelength‐selective ON/OFF ratio. The system that was explored is a fac‐[Re(CO)3(TTF‐DPPZ)Cl] complex, where TTF‐DPPZ=4',5'‐bis(propylthio)tetrathiafulvenyl[i]dipyrido[3,2‐a:2',3'‐c]phenazine. DFT calculations and AC‐Stark spectroscopy confirmed the presence of two distinct optically active charge‐transfer processes, namely a metal‐to‐ligand charge transfer (MLCT) and an intra‐ligand charge transfer (ILCT). Ultrafast transient absorption measurements showed that the ILCT state decays in the ps regime. Upon excitation to the MLCT state, only a long‐lived 3MLCT state was observed after 80 ps. Remarkably, however, the bleaching of the ILCT absorption band remained as a result of the effective inhibition of the HOMO–LUMO transition. [ABSTRACT FROM AUTHOR]

To develop new and flexible CuI containing luminescent substances, we extend our previous investigations on two metal‐centered species to four metal‐centered complexes. These complexes could be a basis for designing new organic light‐emitting diode (OLED) relevant species. Both the synthesis and in‐depth spectroscopic analysis, combined with high‐level theoretical calculations are presented on a series of tetranuclear CuI complexes with a halide containing Cu4X4 core (X=iodide, bromide or chloride) and two 2‐(diphenylphosphino)pyridine bridging ligands with a methyl group in para (4‐Me) or ortho (6‐Me) position of the pyridine ring. The structure of the electronic ground state is characterized by X‐ray diffraction, NMR, and IR spectroscopy with the support of theoretical calculations. In contrast to the para system, the complexes with ortho‐substituted bridging ligands show a remarkable and reversible temperature‐dependent dual phosphorescence. Here, we combine for the first time the luminescence thermochromism with time‐resolved FTIR spectroscopy. Thus, we receive experimental data on the structures of the two triplet states involved in the luminescence thermochromism. The transient IR spectra of the underlying triplet metal/halide‐to‐ligand charge transfer (3M/XLCT) and cluster‐centered (3CC) states were obtained and interpreted by comparison with calculated vibrational spectra. The systematic and significant dependence of the bridging halides was analyzed. [ABSTRACT FROM AUTHOR]

One‐electron reduced metal complexes derived from photoactive ruthenium or iridium complexes are important intermediates for substrate activation steps in photoredox catalysis and for the photocatalytic generation of solar fuels. However, owing to the heavy atom effect, direct photochemical pathways to these key intermediates suffer from intrinsic efficiency problems resulting from rapid geminate recombination of radical pairs within the so‐called solvent cage. In this study, we prepared and investigated molecular dyads capable of producing reduced metal complexes via an indirect pathway relying on a sequence of energy and electron transfer processes between a Ru complex and a covalently connected anthracene moiety. Our test reaction to establish the proof‐of‐concept is the photochemical reduction of ruthenium(tris)bipyridine by the ascorbate dianion as sacrificial donor in aqueous solution. The photochemical key step in the Ru‐anthracene dyads is the reduction of a purely organic (anthracene) triplet excited state by the ascorbate dianion, yielding a spin‐correlated radical pair whose (unproductive) recombination is strongly spin‐forbidden. By carrying out detailed laser flash photolysis investigations, we provide clear evidence for the indirect reduced metal complex generation mechanism and show that this pathway can outperform the conventional direct metal complex photoreduction. The further optimization of our approach involving relatively simple molecular dyads might result in novel photocatalysts that convert substrates with unprecedented quantum yields. [ABSTRACT FROM AUTHOR]

Manganese‐mediated borylation of aryl/heteroaryl diazonium salts emerges as a general and versatile synthetic methodology for the synthesis of the corresponding boronate esters. The reaction proved an ideal testing ground for delineating the Mn species responsible for the photochemical reaction processes, that is, involving either Mn radical or Mn cationic species, which is dependent on the presence of a suitably strong oxidant. Our findings are important for a plethora of processes employing Mn‐containing carbonyl species as initiators and/or catalysts, which have considerable potential in synthetic applications. [ABSTRACT FROM AUTHOR]

Six pyrimidine‐based push–pull systems substituted at positions C2 and C4/6 with phenylacridan and styryl moieties, employing methoxy or N,N‐diphenylamino donors, have been designed and synthesized through cross‐coupling and Knoevenagel reactions. X‐ray analysis confirmed that the molecular structure featured the acridan moiety arranged perpendicularly to the residual π system. Photophysical studies revealed significant differences between the methoxy and N,N‐diphenylamino chromophores. Solvatochromic studies revealed that the methoxy derivatives showed dual emission in polar solvents. Time‐resolved spectroscopy revealed that the higher energy band involved very fast (<80 ps) fluorescence, whereas the lower energy one included long components (≈30 ns) due to long‐lived intramolecular charge‐transfer fluorescence. In contrast to N,N‐diphenylamino chromophores, the methoxy derivatives also showed aggregation‐induced emission in mixtures of THF/water, as well as dual emission in thin films, covering almost the whole visible spectrum with corresponding chromaticity coordinates not far from that of pure white light. These properties render the methoxy derivatives as very promising organic materials for white organic light‐emitting diodes. [ABSTRACT FROM AUTHOR]

A semiconductor‐metal‐complex hybrid photocatalyst was previously reported for CO2 reduction; this photocatalyst is composed of nitrogen‐doped Ta2O5 as a semiconductor photosensitizer and a Ru complex as a CO2 reduction catalyst, operating under visible light (>400 nm), with high selectivity for HCOOH formation of more than 75 %. The electron transfer from a photoactive semiconductor to the metal‐complex catalyst is a key process for photocatalytic CO2 reduction with hybrid photocatalysts. Herein, the excited‐state dynamics of several hybrid photocatalysts are described by using time‐resolved emission and infrared absorption spectroscopies to understand the mechanism of electron transfer from a semiconductor to the metal‐complex catalyst. The results show that electron transfer from the semiconductor to the metal‐complex catalyst does not occur directly upon photoexcitation, but that the photoexcited electron transfers to a new excited state. On the basis of the present results and previous reports, it is suggested that the excited state is a charge‐transfer state located between shallow defects of the semiconductor and the metal‐complex catalyst. [ABSTRACT FROM AUTHOR]

Quinoline photobases exhibit a distinctly higher pKa in their electronically excited state than in the ground state, thereby enabling light‐controlled proton transfer reactions, for example, in molecular catalysis. The absorption of UV light translates to a pKa jump of approximately 10 units, as established for small‐molecule photobases. This contribution presents the first synthesis of quinoline‐based polymeric photobases prepared by reversible addition‐fragmentation chain‐transfer (RAFT) polymerization. The integration of quinolines as photobase chromophores within copolymers offers new possibilities for light‐triggered proton transfer in nanostructured materials, that is, in nanoparticles, at surfaces, membranes and interfaces. To exploit the light‐triggered reactivity of photobases within such materials, we first investigated how the ground‐ and excited‐state properties of the quinoline unit changes upon polymer integration. To address this matter, we combined absorption and emission spectroscopy with time‐resolved transient‐absorption studies to reveal photoinduced proton‐transfer dynamics in various solvents. The results yield important insights into the thermodynamic and kinetic properties of these polymeric quinoline photobases. [ABSTRACT FROM AUTHOR]

Phytochrome photoreceptors operate via photoisomerization of a bound bilin chromophore. Their typical architecture consists of GAF, PAS and PHY domains. Knotless phytochromes lack the PAS domain, while retaining photoconversion abilities, with some being able to photoconvert with just the GAF domain. Therefore, we investigated the ultrafast photoisomerization of the Pr state of a knotless phytochrome to reveal the effect of the PHY domain and its "tongue" region on the transduction of the light signal. We show that the PHY domain does not affect the initial conformational dynamics of the chromophore. However, it significantly accelerates the consecutively induced reorganizational dynamics of the protein, necessary for the progression of the photoisomerization. Consequently, the PHY domain keeps the bilin and its binding pocket in a more reactive conformation, which decreases the extent of protein reorganization required for the chromophore isomerization. Thereby, less energy is lost along nonproductive reaction pathways, resulting in increased efficiency. [ABSTRACT FROM AUTHOR]

Ultrafast time‐resolved infrared (TRIR) is used to report on the binding site of the [Ru(phen)2(dppz)]2+ "light‐switch" complex with both bimolecular (Oxytricha nova telomere) and intramolecular (human telomere) guanine‐quadruplex structures in both K+ and Na+ containing solutions. TRIR permits the simultaneous monitoring both of the "dark" and "bright" states of the complex and of the quadruplex nucleobase bases, the latter via a Stark effect induced by the excited state of the complex. These data are used to establish the contribution of guanine base stacking and loop interactions to the binding site of this biologically relevant DNA structure in solution. A particularly striking observation is the strong thymine signal observed for the Na+ form of the human telomere sequence, which is expected to be in the anti‐parallel conformation. [ABSTRACT FROM AUTHOR]

As a novel rylene type dye a diimine ligand with a fully rigid and extended π‐system in its backbone was prepared by directly fusing a 1,10‐phenanthroline building block with 1,8‐naphthalimide. The corresponding heteroleptic ruthenium photosensitizer bearing one biipo and two tbbpy ligands was synthesized and extensively analyzed by a combination of NMR, single crystal X‐ray diffraction, steady‐state absorption and emission, time‐resolved spectroscopy and different electrochemical measurements supported by time‐dependent density functional theory calculations. The cyclic and differential pulse voltammograms revealed, that the naphthaloylenebenzene moiety enables an additional second reduction of the ligand. Moreover, this ligand possesses a very broad absorption in the visible region. In the RuII complex this causes an overlap of ligand‐centered and metal‐to‐ligand charge transfer transitions. The emission of the complex is clearly redshifted compared to the ligand emission with very long‐lived excited states lifetimes of 1.7 and 24.7 μs in oxygen‐free acetonitrile solution. This behavior is accompanied by a surprisingly high oxygen sensitivity. Finally, this photosensitizer was successfully applied for the effective evolution of singlet oxygen challenging some of the common RuII prototype complexes. [ABSTRACT FROM AUTHOR]

The lipophilic nature of organic dyes complicates their effectiveness in aqueous solutions. In this work we investigate three different strategies for achieving water‐solubility of the diazaoxatriangulenium (DAOTA+) chromophore: hydrophilic counter ions, aromatic sulfonation of the chromophore, and attachment of charged side chains. The long fluorescence lifetime (FLT, τf=20 ns) of DAOTA+ makes it a sensitive probe to analyze solvation and aggregation effects. Direct sulfonation of the chromophore was found to increase solubility drastically, but at the cost of greatly reduced quantum yields (QYs) due to enhanced non‐radiative deactivation processes. The introduction of either cationic (4) or zwitterionic side chains (5), however, brings the FLT (τf=18 ns) and QY (ϕf=0.56) of the dye to the same level as the parent chromophore in acetonitrile. Time‐resolved fluorescence spectroscopy also reveals a high resistance to aggregation and non‐specific binding in a high loading of bovine serum albumin (BSA). The results clearly show that addition of charged flexible side chains is preferable to direct sulfonation of the chromophore core. [ABSTRACT FROM AUTHOR]

The light‐gated organocatalysis via the release of 4‐N,N‐dimethylaminopyridine (DMAP) by irradiation of the [Ru(bpy)2(DMAP)2]2+ complex with visible light was investigated. As model reaction the acetylation of benzyl alcohols with acetic anhydride was chosen. The pre‐catalyst releases one DMAP molecule on irradiation at wavelengths longer than 455 nm. The photochemical process was characterized by steady‐state irradiation and ultrafast transient absorption spectroscopy. The latter enabled the observation of the 3MLCT state and the spectral features of the penta‐coordinated intermediate [Ru(bpy)2(DMAP)]2+. The released DMAP catalyzes the acetylation of a wide range of benzyl alcohols with chemical yields of up to 99 %. Control experiments revealed unequivocally that it is the released DMAP which takes the role of the catalyst. [ABSTRACT FROM AUTHOR]

Time‐resolved X‐ray (Tr‐XAS) and optical transient absorption (OTA) spectroscopy on the pico‐microsecond timescale coupled with density functional theory calculations are applied to study the light‐induced spin crossover processes of a Fe‐based macrocyclic complex in solution. Tr‐XAS analysis after light illumination shows the formation of a seven‐coordinated high‐spin quintet metastable state, which relaxes to a six‐coordinated high‐spin configuration before decaying to the ground state. Kinetic analysis of the macrocyclic complex reveals an unprecedented long‐lived decay lifetime of approximately 42.6 μs. Comparative studies with a non‐macrocyclic counterpart illustrate a significantly shortened approximately 568‐fold decay lifetime of about 75 ns, and highlight the importance of the ligand arrangement in stabilizing the reactivity of the excited state. Lastly, OTA analysis shows the seven‐coordinated high‐spin state to be formed within approximately 6.2 ps. These findings provide a complete understanding of the spin crossover reaction and relaxation pathways of the macrocyclic complex, and reveal the importance of a flexible coordination environment for their rational design. [ABSTRACT FROM AUTHOR]

The dye rhodamine 6G can act as a photocatalyst through photoinduced electron transfer. After electronic excitation with green light, rhodamine 6G takes an electron from an electron donor, such as N,N‐diisopropylethylamine, and forms the rhodamine 6G radical. This radical has a reduction potential of around −0.90 V and can split phenyl iodide into iodine anions and phenyl radicals. Recently, it has been reported that photoexcitation of the radical at 420 nm splits aryl bromides into bromide anions and aryl radicals. This requires an increase in reduction potential, hence the electronically excited rhodamine 6G radical was proposed as the reducing agent. Here, we present a study of the mechanism of the formation and photoreactions of the rhodamine 6G radical by transient absorption spectroscopy in the time range from femtoseconds to minutes in combination with quantum chemical calculations. We conclude that one photon of 540 nm light produces two rhodamine 6G radicals. The lifetime of the photoexcited radicals of around 350 fs is too short to allow diffusion‐controlled interaction with a substrate. A fraction of the excited radicals ionize spontaneously, presumably producing solvated electrons. This decay produces hot rhodamine 6G and hot rhodamine 6G radicals, which cool with a time constant of around 10 ps. In the absence of a substrate, the ejected electrons recombine with rhodamine 6G and recover the radical on a timescale of nanoseconds. Photocatalytic reactions occur only upon excitation of the rhodamine 6G radical, and due to its short excited‐state lifetime, the electron transfer to the substrate probably takes place through the generation of solvated electrons as an additional step in the proposed photochemical mechanism. [ABSTRACT FROM AUTHOR]

Light‐induced activation of biomolecules by uncaging of photolabile protection groups has found many applications for triggering biochemical reactions with minimal perturbations directly within cells. Such an approach might also offer unique advantages for solid‐state NMR experiments on membrane proteins for initiating reactions within or at the membrane directly within the closed MAS rotor. Herein, we demonstrate that the integral membrane protein E. coli diacylglycerol kinase (DgkA), which catalyzes the phosphorylation of diacylglycerol, can be controlled by light under MAS‐NMR conditions. Uncaging of NPE‐ATP or of lipid substrate NPE‐DOG by in situ illumination triggers its enzymatic activity, which can be monitored by real‐time 31P‐MAS NMR. This proof‐of‐concept illustrates that combining MAS‐NMR with uncaging strategies and illumination methods offers new possibilities for controlling biochemical reactions at or within lipid bilayers. [ABSTRACT FROM AUTHOR]

Intersystem crossing (ISC) was observed for naphthalimide (NI)‐derived Tröger's base, and the ISC was confirmed to occur by a spin‐orbital charge‐transfer (SOCT) mechanism. Conventional electron donor/acceptor dyads showing SOCT‐ISC have semirigid linkers. In contrast, the linker between the two chromophores in Tröger's base is rigid and torsion is completely inhibited, which is beneficial for efficient SOCT‐ISC. Femtosecond transient absorption (TA) spectra demonstrated charge‐separation and charge‐recombination‐induced ISC processes. Nanosecond TA spectroscopy confirmed the ISC, and the triplet state is long‐lived (46 μs, room temperature). The ISC quantum yield is dependent on solvent polarity (8–41 %). The triplet state was studied by pulsed‐laser‐excited time‐resolved EPR spectroscopy, and both the NI‐localized triplet state and triplet charge‐transfer state were observed, which is in good agreement with the spin‐density analysis. The Tröger's base was confirmed to be a potent photodynamic therapy reagent with HeLa cells (EC50=5.0 nm). [ABSTRACT FROM AUTHOR]

Site‐specific isotopic labeling of molecules is a widely used approach in IR spectroscopy to resolve local contributions to vibrational modes. The induced frequency shift of the corresponding IR band depends on the substituted masses, as well as on hydrogen bonding and vibrational coupling. The impact of these different factors was analyzed with a designed three‐stranded β‐sheet peptide and by use of selected 13C isotope substitutions at multiple positions in the peptide backbone. Single‐strand labels give rise to isotopically shifted bands at different frequencies, depending on the specific sites; this demonstrates sensitivity to the local environment. Cross‐strand double‐ and triple‐labeled peptides exhibited two resolved bands that could be uniquely assigned to specific residues, the equilibrium IR spectra of which indicated only weak local‐mode coupling. Temperature‐jump IR laser spectroscopy was applied to monitor structural dynamics and revealed an impressive enhancement of the isotope sensitivity to both local positions and coupling between them, relative to that of equilibrium FTIR spectroscopy. Site‐specific relaxation rates were altered upon the introduction of additional cross‐strand isotopes. Likewise, the rates for the global β‐sheet dynamics were affected in a manner dependent on the distinct relaxation behavior of the labeled oscillator. This study reveals that isotope labels provide not only local structural probes, but rather sense the dynamic complexity of the molecular environment. [ABSTRACT FROM AUTHOR]

Inspired by the sulfur‐rich environment found in active hydrogenase enzymes, a Ni‐based proton reduction catalyst with pentadentate N2S3 ligand was synthesised. When coupled with [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N2S2 ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time‐resolved X‐ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The NiII catalyst undergoes a photoinduced metal‐centred reduction to form a NiI intermediate with distorted square‐bipyramidal geometry. Further kinetic analyses revealed differences in charge‐separation dynamics between the pentadentate and tetradentate forms. [ABSTRACT FROM AUTHOR]

A series of seven homoleptic CuI complexes based on hetero‐bidentate P^N ligands was synthesized and comprehensively characterized. In order to study structure–property relationships, the type, size, number and configuration of substituents at the phosphinooxazoline (phox) ligands were systematically varied. To this end, a combination of X‐ray diffraction, NMR spectroscopy, steady‐state absorption and emission spectroscopy, time‐resolved emission spectroscopy, quenching experiments and cyclic voltammetry was used to assess the photophysical and electrochemical properties. Furthermore, time‐dependent density functional theory calculations were applied to also analyze the excited state structures and characteristics. Surprisingly, a strong dependency on the chirality of the respective P^N ligand was found, whereas the specific kind and size of the different substituents has only a minor impact on the properties in solution. Most importantly, all complexes except C3 are photostable in solution and show fully reversible redox processes. Sacrificial reductants were applied to demonstrate a successful electron transfer upon light irradiation. These properties render this class of photosensitizers as potential candidates for solar energy conversion issues. [ABSTRACT FROM AUTHOR]

Spin–orbit charge‐transfer intersystem crossing (SOCT‐ISC) is useful for the preparation of heavy atom‐free triplet photosensitisers (PSs). Herein, a series of perylene‐Bodipy compact electron donor/acceptor dyads showing efficient SOCT‐ISC is prepared. The photophysical properties of the dyads were studied with steady‐state and time‐resolved spectroscopies. Efficient triplet state formation (quantum yield ΦT=60 %) was observed, with a triplet state lifetime (τT=436 μs) much longer than that accessed with the conventional heavy atom effect (τT=62 μs). The SOCT‐ISC mechanism was unambiguously confirmed by direct excitation of the charge transfer (CT) absorption band by using nanosecond transient absorption spectroscopy and time‐resolved electron paramagnetic resonance (TREPR) spectroscopy. The factors affecting the SOCT‐ISC efficiency include the geometry, the potential energy surface of the torsion, the spin density for the atoms of the linker, solvent polarity, and the energy matching of the 1CT/3LE states. Remarkably, these heavy atom‐free triplet PSs were demonstrated as a new type of efficient photodynamic therapy (PDT) reagents (phototoxicity, EC50=75 nm), with a negligible dark toxicity (EC50=78.1 μm) compared with the conventional heavy atom PSs (dark toxicity, EC50=6.0 μm, light toxicity, EC50=4.0 nm). This study provides in‐depth understanding of the SOCT‐ISC, unveils the design principles of triplet PSs based on SOCT‐ISC, and underlines their application as a new generation of potent PDT reagents. [ABSTRACT FROM AUTHOR]

The interlocking of ring and axle molecular components in rotaxanes provides a way to combine chromophoric, electron‐donor and electron‐acceptor moieties in the same molecular entity, in order to reproduce the features of photosynthetic reaction centers. To this aim, the photoinduced electron transfer processes involving a 1,8‐naphthalimide chromophore, embedded in several rotaxane‐based dyads, were investigated by steady‐state and time‐resolved absorption and luminescence spectroscopic experiments in the 300 fs–10 ns time window. Different rotaxanes built around the dialkylammonium/ dibenzo[24]crown‐8 ether supramolecular motif were designed and synthesized to decipher the relevance of key structural factors, such as the chemical deactivation of the ammonium‐crown ether recognition, the presence of a secondary site for the ring along the axle, and the covalent functionalization of the macrocycle with a phenothiazine electron donor. Indeed, the conformational freedom of these compounds gives rise to a rich dynamic behavior induced by light and may provide opportunities for investigating and understanding phenomena that take place in complex (bio)molecular architectures. [ABSTRACT FROM AUTHOR]