Photoinduced Intermolecular Electron Transfer Research Articles

Intermolecular Photoinduced Electron Transfer in Biosystems: Impact of Conformational Transitions and Multiple Channels on Kinetics

AbstractEstimating the kinetics of electron transfer (ET) processes in biologically relevant systems using theoretical‐computational methods remains a formidable task. This challenge arises from the inherent complexity of these systems, which makes it impractical to apply a fully quantum‐mechanical treatment. Hybrid quantum mechanical/classical mechanical computational approaches have been devised to enable the explicit simulation of electron transfer kinetics. This concept article focuses on a specific theoretical‐computational method employed in this context, namely the Perturbed Matrix Method (PMM), which has the merit of being able to include large‐scale conformational effects in the ET kinetics and potential multiple, alternative, ET channels. We describe its underlying physical principles, examine its advantages and limitations, and offer insights into its applications. Examples of the approach are discussed in the context of estimating photo‐induced electron transfer kinetics in proteins. The non‐exponential behavior observed in the presented case studies mainly arises from an active coupling with the environment fluctuations, but also partly stems from the presence of branching ET pathways.

Photo-Induced Disproportionation-Mediated Photodynamic Therapy: Simultaneous Oxidation of Tetrahydrobiopterin and Generation of Superoxide Radicals.

We herein present an approach of photo-induced disproportionation for preparation of Type-I photodynamic agents. As a proof of concept, BODIPY-based photosensitizers were rationally designed and prepared. The photo-induced intermolecular electron transfer between homotypic chromophores leads to the disproportionation reaction, resulting in the formation of charged intermediates, cationic and anionic radicals. The cationic radicals efficiently oxidize the cellularimportant coenzyme, tetrahydrobiopterin (BH4 ), and the anionic radicals transfer electrons to oxygen to produce superoxide radicals (O2 - ⋅). One of our Type-I photodynamic agents not only self-assembles in water but also effectively targets the endoplasmic reticulum. It displayed excellent photocytotoxicity even in highly hypoxic environments (2 % O2 ), with a half-maximal inhibitory concentration (IC50 ) of 0.96 μM, and demonstrated outstanding antitumor efficacy in murine models bearing HeLa tumors.

Eosin Y-Based Metal-Organic Framework Synergistic with Cobalt(II) Complex for Hydrogen Evolution through Photoinduced Intermolecular Electron Transfer.

Photocatalytic hydrogen evolution reaction (HER) is a promising approach for producing clean energy and has the potential to play an important role in the transition toward a more sustainable and environmentally friendly energy system. Optimizing the photoinduced electron transfer (PET) process and increasing visible-light utilization play a central role in photocatalysis. Herein, we built a novel Eosin Y-based metal-organic framework (Zn-EYTP) by synergizing a cobalt(II) complex for boosting the H2 evolution efficiency through photoinduced intermolecular electron transfer. Under optimized conditions, the maximum H2 evolution efficiency for Zn-EYTP was determined to be a turnover number (TON) value of 11,100 under green LED irradiation. And the synthesized Zn-EYTP photocatalysts could be easily recycled to restore the initial photocatalytic activity even after 3 cycles. Detailed studies reveal that the significantly enhanced HER activity in Zn-EYTP could be ascribed to the effective separation of photogenerated charges and the synergistic intermolecular interaction between Zn-EYTP and [Co(bpy)3]Cl2. The present work enables a deeper understanding of the importance of the PET process for enhanced HER photocatalytic activities, which will provide a viable strategy for the development of highly efficient photocatalysts.

Dual Photo-/Electrochromic Pyromellitic Diimide-Based Coordination Polymer.

By the combination of N,N'-bis(carboxymethyl)-pyromellitic diimide (H2CMPMD, 1) and zinc ions, a novel PMD-based coordination polymer (CP), [Zn(CMPMD)(DMF)1.5]·0.5DMF (2) (DMF = N,N'-dimethylformamide), has been prepared and characterized. 1 and 2 exhibit completely different photochromic properties, which are mainly reflected in the photoresponsive rate (5 s for 1 vs 1 s for 2) and coloration contrast (from colorless to light green for 1 vs green for 2). This phenomenon should be attributed to the introduction of zinc ions and the consequent formation of the distinct interfacial contacts of electron donors (EDs) and electron acceptors (EAs) (dn-π = 3.404 and 3.448 Å for 1 vs dn-π = 3.343, 3.359, 3.398, and 3.495 Å for 2), suggesting a subtle modulating effect of metal ions on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photochromic behaviors. Interestingly, the photochromic performance of 2 can be enhanced after the removal of coordinated DMF, which might be ascribed to the decrease of the distance of EDs/EAs caused by lattice shrinkage, which further improves the efficiency of PIET. Meanwhile, 2 displays rapid electrochromic behavior with an obvious reversible color change from colorless to green, which can be used in an electrochromic device. This work develops a new type of EA for the construction of stimuli-responsive functional materials with excellent dual photo-/electrochromic properties.

Modulating Photoinduced Electron Transfer between Photosensitive MOF and Co(II) Proton Reduction Sites forBoosting Photocatalytic Hydrogen Production.

Photocatalytic hydrogen production viawater splitting is the subject of intense research. Photoinduced electron transfer (PET) between a photosensitizer (PS) and a proton reduction catalyst is a prerequisite step and crucial to affecting hydrogen production efficiency. Herein, three photoactive metal-organic framework (MOF) systems having two different PET processes where PS and Co(II) centers are either covalently bonded or coexisting to drive photocatalytic H2 production arebuilt. Compared to these two intramolecular PET systems including CoII -Zn-PDTP prepared from the post-synthetic metalation toward uncoordinated pyridine N sites of Zn-PDTP and sole cobalt-based MOF Co-PDTP, the CoII (bpy)3 @Zn-PDTP system impregnated by molecular cocatalyst possessing intermolecular PET process achieves the highest H2 evolution rate of 116.8mmol g-1 h-1 over a period of 10h, about 7.5 and 9.3 times compared to CoII -Zn-PDTP and Co-PDTP in visible-light-driven H2 evolution, respectively. Further studies reveal that the enhanced photoactivity in CoII (bpy)3 @Zn-PDTP canbe ascribed to the high charge-separation efficiency of Zn-PDTP and the synergistic intermolecular interaction between Zn-PDTP and cobalt complexes. The present work demonstrates that the rational design of PET process between MOFs and catalytic metal sites can be a viable strategy for the development of highly efficient photocatalysts with enhanced photocatalytic activities.

Study on New Dental Materials Containing Quinoxaline-Based Photoinitiators in Terms of Exothermicity of the Photopolymerization Process.

Modern dentistry places great demands on the dental composites used for filling tooth cavities or treating cavitated tooth decay. The aim of the work was to modify the properties of composites by changing the initiators and co-initiators. This was achieved by using initiators based on a quinoxaline skeleton and co-initiators that are derivatives of acetic acid, which is an advantage of these photoinitiating systems due to the elimination of aromatic amines from the photocurable composition. The composites also differed in dental fillers. The effect of the compounds on the exothermicity of the photopolymerization process, the surface morphology of the obtained materials and the maximum compressive strength were determined. The photoinitiating capacity of the two-component systems was tested by the microcalorimetric method using the multifunctional monomer TMPTA, typical for dental filler compositions. The new photoinitiating systems show particularly good efficiency of free radical polymerization initiation, which occurs by the photoinduced intermolecular electron transfer (PET) mechanism. The comparison of the tested systems with camphorquinone, a photoinitiator traditionally used in dentistry, made it possible to observe a decrease in temperature during photopolymerization without a significant decrease in the polymerization rate or increase in photocuring time, as well as a better homogeneity of the surface of the obtained polymeric materials. This indicates that dye-acetic acid derivative systems may be useful in dental applications.

The effect of conjugation degree of aromatic carboxylic acids on electronic and photo-responsive behaviors of naphthalenediimide-based coordination polymers.

Three novel naphthalenediimide-based (NDI-based) coordination polymers (CPs), namely [Cd(3-PMNDI)(2,2'-BPDC)] (1), [Cd2(3-PMNDI)1.5(4,4'-BPDC)2(H2O)3]·DMF (2) and [Cd(3-PMNDI)(4,4'-SDC)] (3) (2,2'-H2BPDC = 2,2'-biphenyldicarboxylic acid, 4,4'-H2BPDC = 4,4'-biphenyldicarboxylic acid, 4,4'-H2SDC = 4,4'-stilbenedicarboxylic acid, 3-PMNDI = N,N'-bis(3-pyridylmethyl)-1,4,5,8-naphthalenediimide, and DMF = N,N'-dimethylformamide), have been designed and synthesized here from electron-deficient PMNDI (electron acceptors, EAs) and electron-rich aromatic carboxylic acids (electron donors, EDs) in the presence of cadmium ions. The introduction of aromatic carboxylic acids with different sizes and conjugation degrees leads to the generation of a two-dimensional (2D) layer in 1, a two-fold interpenetrated three-dimensional (3D) network in 2 and an eight-fold interpenetrated 3D framework in 3. Furthermore, the use of distinct electron-donating aromatic carboxylic acids and the consequent different numbers and strengths of lone pair-π and π-π interactions in the interfacial contacts of EDs/EAs give rise to distinct intermolecular charge transfer (ICT) and initial colors of the three CPs, and consequently cause different photoinduced intermolecular electron transfer (PIET) and distinguishing photo-responsive behaviors (weak photochromic performance for 1, excellent photochromic properties for 2 and non-photochromism for 3). This study indicates that an appropriate ICT is beneficial for PIET, but too weak or too strong ICT is not conducive to PIET, which provides an effective strategy for the construction of functional CPs with distinguishing photo-responsive properties through the subtle balance of ICT and PIET.

The modulation effect of auxiliary ligands on photochromic properties of 3D naphthalene diimide coordination polymers.

Two novel naphthalene diimide (NDI) coordination polymers (CPs), [Cd(NicNDI)(4,4'-SBC)] (1) and [Cd(NicNDI)(2,2'-BPC)] (2) (NicNDI = (3-pyridylacylamino)-1,4,5,8-naphthalene diimide, 4,4'-SBC = 4,4'-stilbene dicarboxylic acid, 2,2'-BPC = 2,2'-biphenyl dicarboxylic acid), were designed and prepared by the combination of electron-deficient NicNDI and electron-rich aromatic carboxylic acid ligands in the presence of cadmium ions. The usage of aromatic carboxylic acid ligands with different conjugation degrees, sizes, shapes and charge densities leads to the generation of distinct interpenetrated three-dimensional (3D) frameworks. Interestingly, photochromism of 1 and weak photoactivity of 2 should be attributed to the introduction of different auxiliary ligands and consequently the formation of distinct interfacial contacts of electron donors (EDs)/electron acceptors (EAs) (dπ-π = 3.427 Å, infinite -ED-EA-ED-EA- for 1vs. dπ-π = 3.634 Å, discrete ED-EA-ED for 2), suggesting a subtle modulating effect of auxiliary ligands on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photoresponsive behaviors.

Photoinduced electron transfer between a noble-metal-free [Mo6I8Cl6]2- cluster and polyoxometalates.

Evidence for photoinduced intermolecular electron transfer from the excited state of the [Mo6I8Cl6]2- electron-rich cluster to polyoxometalates (POMs) is reported. We demonstrate that the global charge density of POMs affects the efficiency of electron transfer. This work paves the way for the rational design of photocatalytic systems using cluster-based complexes as robust noble-metal-free photosensitizers.

A turn-on fluorescent Zn(II) metal-organic framework sensor for quantitative anthrax biomarker detection.

2,6-Pyridine dicarboxylic acid (DPA) is considered one of the main anthrax biomarkers, and the detection of DPA is of great significance. This work presents a Zn(II)-based metal-organic framework (MOF) with the formula {[Zn2(2,6-NBC)2(vlpy)Zn(2,6-NBC)(vlpy)0.5]·0.8(2,6-H2NBC)·H2O}n (1) assembled from 2,6-naphthalenedicarboxylic acid (2,6-H2NBC) and 4,4'-vinylenedipyridine (vlpy) for a photoluminescence sensor matrix for DPA detection. 1 features a 3D pillar-layer framework with nanopore sizes of ca.13.165 Å × 12.731 Å, 12.725 Å × 11.018 Å and 13.114 Å × 13.165 Å along the three directions, occupied by lattice water and disordered 2,6-H2NBC molecules. The obtained 1 can be used as a turn-on fluorescence sensor for the detection of DPA with high selectivity, excellent sensitivity and recyclability. The luminescence of 1 demonstrates an obvious color change from blue to purplish blue as the DPA concentration rises. Furthermore, a linear correlation is presented between the fluorescence and a low DPA concentration of 0-0.3 mM, and the detection limit can reach as low as 128 nM, much lower than that of an infectious dose to a human of anthrax spores (60 μM). A fluorescence test paper is fabricated to detect DPA rapidly through color change. DFT calculations indicate the intermolecular photoinduced electron-transfer transition and hydrogen-bonding interaction between DPA molecules and the skeleton of 1 induces the "turn-on" fluorescence sensing of DPA behavior.

Photoinitiation abilities of indeno- and indoloquinoxaline derivatives and mechanical properties of dental fillings based on multifunctional acrylic monomers and glass ionomer

Photopolymerization is a rapidly expanding technology with a wide variety of applications, from imaging to biomedical uses. Here, we present enhanced photosensitization of polymerization by photoredox pairs based on indene- and indoloquinoxaline dyes and thiophenoxyacetic acid for dental applications. The photoinitiating ability of the two-component systems was tested using several multifunctional monomers of various structures typical for dental fillings. The new photoinitiating systems show excellent efficiency in initiating free radical polymerization which occurs by photoinduced intermolecular electron transfer (PET) mechanism. Modification of the dye structure by extending the chain of conjugated π bonds, the arrangement of aromatic rings and the type of heteroatom, allowed to change the spectroscopic properties of the tested compounds and use them as absorbers of light emitted by dental lamps. The improved mechanical properties of the cured polymers, i.e., lowering the temperature during photopolymerization and an increase in polymer hardness were observed for the proposed photoinitiating systems compared to the camphorquinone – photoinitiator traditionally used in dentistry. This indicates that the dye – thiophenoxyacetic acid systems may be useful as photoinitiators in dental applications. The undoubted advantage of these photoinitiating systems is the elimination of the toxic aromatic amines traditionally used as co-initiators from the dental composition. It was possible thanks to the use of thiophenoxyacetic acid. Its application does not reduce the polymerization rate and does not extend the photocuring time.

Solvent-Modulated Self-Assembly of Naphthalenediimide-Based Cd(II) Complexes and the Controllable Photochromism via Conformational Isomerization.

Rational regulation of the properties of photochromic materials is a challenging and meaningful work. In the present work, NDI-based complexes, namely, [Cd0.5(NDI)(HBDC)]·H2O (1) and a series of conformational isomers of {[Cd(NDI)0.5(BDC)]·MeCN}n (2), were synthesized by varying the solvent conditions (H2BDC = terephthalic acid, NDI = N,N'-bis(3-pyridylcarbonylhydrazine)-1,4,5,8-naphthalene diimide). Complex 1 exhibits a 0D mononuclear structure without photochromic behavior due to the bad conjugation of the naphthalene diimide moiety. The conformational isomers of complex 2 manifest a 3D network, showing ultra-fast photo-induced intermolecular electron transfer photochromic behavior under X-ray, UV, and visible light. However, they show different photochromic rates and coloring contrast upon photoirradiation, which originates from their difference in the distances of lone pair(COO)···π(NDI). This was realized via controlling the solvent ratio in the reaction system. In addition, compared to UV/X-ray light, 2 exhibits greater sensitivity to visible light and is an organic-inorganic hybrid material with photomodulated luminescence. Based on the excellent performance, complex 2 can be applied to filter paper, showing potential applications as an inkless printing medium and selective perception of ammonia and amine vapors in the solid state via different visual color changes.

Photochemistry of pyruvic acid is governed by photo-induced intermolecular electron transfer through hydrogen bonds.

Despite more than 85 years of research, the mechanism behind the photodecarboxylation of pyruvic acid remains elusive. Most studies focused on the gas and liquid phase of diluted solutions of pyruvic acid to understand the impact of sun light on the degradation of this molecule in the atmosphere. By analyzing concentrated supercooled solutions at 77 K, we demonstrate that instead of decarboxylating, the pyruvic acid molecule plays the role of electron donor and transfers an electron to an acceptor molecule that subsequently degrades to form CO2. We show that this electron transfer occurs via hydrogen bonding and that in aqueous solutions of pyruvic acid, the hydrated form is the electron acceptor. These findings demonstrate that photo-induced electron transfer via hydrogen bonding can occur between two simple carboxylic acids and that this mechanism governs the photochemistry of pyruvic acid, providing unexplored alternative pathways for the decarboxylation of photo-inactive molecules.

Acenaphthoquinoxaline Derivatives as Dental Photoinitiators of Acrylates Polymerization.

A series of dyes based on the acenaphthoquinoxaline skeleton was synthesized. Their structure was modified by introducing electron-withdrawing and electron-donating groups, increasing the number of conjugated double bonds and the number and position of nitrogen atoms, as well as the arrangement of aromatic rings (linear or angular). The dyes were investigated as a component in the photoinitiating systems of radical polymerization for a potential application in dentistry. They acted as the primary absorber of visible light and the acceptor of an electron, which was generated from a second component being an electron donor. Thus, the radicals were generated by the photoinduced intermolecular electron transfer (PET) process. Electron donors used differed in the type of heteroatom, i.e., O, S and N and the number and position of methoxy substituents. To test the ability to initiate the polymerization reaction by photoinduced hydrogen atom transfer, we used 2-mercaptobenzoxazole as a co-initiator. The effectiveness of the photoinitiating systems clearly depends on both the modified acenaphthoquinocaline structure and the type of co-initiator. The lower amount of heat released during the chain reaction and the polymerization rate comparable to this achieved for the photoinitiator traditionally used in dentistry (camphorquinone) indicates that the studied dyes may be valuable in this field.

Synthesis and Photophysics of Water-Soluble Psoralens with Red-Shifted Absorption.

8-Methoxypsoralen (8-MOP) serves as a PUVA (psoralen + UV-A) agent in the treatment of certain skin diseases. Derivatives of 8-MOP with cationic aromatic substituents at the five positions were synthesized and characterized by steady-state, femtosecond and nanosecond spectroscopy as well as cyclic voltammetry. The aromatic substituents' positive charge increases the water solubility and the affinity toward intercalation into DNA. The aromatic substituents were supposed to lower the psoralen S1 energy and thereby suppress a photo-induced electron transfer (PET) with guanine-bearing DNA. Such a suppression of this PET is expected to increase the propensity of psoralens to photo-addition to DNA. For derivatives bearing methylpyridinium residues, femtosecond spectroscopy revealed an intramolecular PET occurring on the picosecond time scale. This PET precludes the population of the triplet state. As triplet states are the precursor state for the photo-addition to DNA, their intermolecular PET renders these derivatives ineffective in terms of PUVA. For two derivatives bearing trimethylphenylammonium moieties, such an intramolecular PET does not occur and the triplet state is populated. Surprisingly, these compounds also exhibit no PUVA activity. Based on these findings, implications for further optimization of PUVA agents are discussed.

How to Manipulate Through-Space Conjugation and Clusteroluminescence of Simple AIEgens with Isolated Phenyl Rings.

Apart from the traditional through-bond conjugation (TBC), through-space conjugation (TSC) is gradually proved as another important interaction in photophysical processes, especially for the recent observation of clusteroluminescence from nonconjugated molecules. However, unlike TBC in conjugated chromophores, it is still challenging to manipulate TSC and clusteroluminescence. Herein, simple and nonconjugated triphenylmethane (TPM) and its derivatives with electron-donating and electron-withdrawing groups were synthesized, and their photophysical properties were systematically studied. TPM was characterized with visible clusteroluminescence due to the intramolecular TSC. Experimental and theoretical results showed that the introduction of electron-donating groups into TPM could red-shift the wavelength and increase the efficiency of clusteroluminescence simultaneously, due to the increased electronic density and stabilization of TSC. However, TPM derivatives with electron-withdrawing groups showed inefficient or even quenched clusteroluminescence caused by the vigorous excited-state intramolecular motion and intermolecular photoinduced electron transfer process. This work provides a reliable strategy to manipulate TSC and clusteroluminescence.

Photophysical and elecron-transfer reaction properties of tris(2,2’-bipyridine)ruthenium(II)-based inhibitors that covalently bound to the active site of chymotrypsin

We have prepared two tris(2,2’-bipyridine)ruthenium(II) complex-based new chymotrypsin (CHT) inhibitors, [Ru(bpy)2(bsfbpy)]Cl2 and [Ru(bsfbpy)3]Cl2 {bsfbpy = 4-methyl-2,2′-bipyridine-4′-carboxylic acid [2-(4-benzenesulfonylfluoride)-ethyl]-amide}. They were covalently modified with Ser195 in the active site of CHT. Photoinduced electron-transfer (ET) systems comprising a Ru-CHT complex and an electron acceptor such as methylviologen (MV2+) were studied. After photoirradiation, the photo-excited triplet state of 2CHT-3{[Ru(bsfbpy)3]2+}* and CHT-3{[Ru(bpy)2(bsfbpy)]}* were both quenched by MV2+ through an intermolecular photoinduced ET mechanism, forming oxidized 2CHT-[Ru(bsfbpy)3]3+ and CHT-[Ru(bpy)2(bsfbpy)]3+, respectively. The intramolecular ET from the amino acid residue of Tyr94 near the active site of CHT proceeded. Transient absorption spectra display the formation of a Tyr●+ radical in the 2CHT-[Ru(bsfbpy)3]2+-MV2+ and the CHT-[Ru(bpy)2(bsfbpy)]2+-MV2+ systems, having a lifetime of 2.24 ms for 2CHT-[Ru(bsfbpy)3]2+-MV2+. The present model system could be one of the available models for the further photochemical reaction of Tyr•+ formed by intramolecular photoinduced ET reactions within a protein scaffold. To clarify the photophysical properties of these Ru inhibitors and their multi step photoinduced ET reactions in the protein matrix, the detailed ET reaction kinetics are discussed.

Achieving UV and X-ray Dual Photochromism in a Metal-Organic Hybrid via Structural Modulation.

Rational design and synthesis of new photochromic sensors have been active research areas of inquiry, particularly on how to predict and tailor their properties and functionalities. Herein, two thulium 2,2':6',2''-terpyridine-4'-carboxylate (TPC)-functionalized metal-organic hybrids, Tm(TPC)2(HCOO)(H2O) (TmTPC-1) and Tm(TPC)(HCOO)2 (TmTPC-2) with different photochromic response behaviors, have been successfully prepared, allowing for straightforward investigations of the structure-property correlation. Single-crystal X-ray diffraction and electron paramagnetic resonance analyses revealed that the incorporation of a unique dangling decorating TPC unit in TmTPC-1 offers a shorter and more accessible π-π interaction pathway between the adjacent TPC moieties than that in TmTPC-2. Such a structural feature leads to the production of radical species via a photoinduced intermolecular electron-transfer (IeMCT) process upon UV or X-ray irradiation, which ultimately endows TmTPC-1 with a rather unusual UV and X-ray dual photochromism. A linear relationship between the change of UV-vis absorbance intensity and X-ray dose was established, making TmTPC-1 a promising dosimeter for X-ray radiation with an extremely high energy threshold (30 kGy). To advance the development for real-world application, we have fabricated polyvinylidene fluoride (PVDF) membranes incorporating TmTPC-1 for functioning either as a UV imager or as an X-ray radiation indicator. Lastly, TmTPC-1 exhibits high thermal stability (up to 400 °C) and radioresistance (at least 900 kGy), and also excellent reversibility of photochromic transformation (at least 5 cycles).

Control of Intermolecular Photoinduced Electron Transfer in Deoxyadenosine-Based Fluorescent Probes.

In this work, we report on the Photoinduced Electron Transfer (PET) reaction between a donor (adenine analogue) and an acceptor (3-methoxychromone dye, 3MC) in the context of designing efficient fluorescent probes as DNA sensors. Firstly, Gibbs energy was investigated in disconnected donor-acceptor systems by Rehm-Weller equation. The oxidation potential of the adenine derivative was responsible for exergonicity of the PET reaction in separated combinations. Then, the PET reaction in donor-π-acceptor conjugates was investigated using steady-state fluorescence spectroscopy, acid-mediated PET inhibition and transient absorption techniques. In conjugated systems, PET is a favorable pathway of fluorescent quenching when an electron-rich adenine analogue (d7A) was connected to the fluorophore (3MC). We found that formation of ground-state complexes even at nm concentration range dominated the dye photophysics and generated poorly emissive species likely through intermolecular PET from d7A to 3MC. On the other hand, solution acidification disrupts complexation and turns on the dye emission. Bridging an electron-poor adenine analogue with high oxidation potential (8 d7A) to 3MC presenting low reduction potential is another alternative to prevent complex formation and produce highly emissive monomer conjugates.

Fluorinated dendritic silicon (IV) phthalocyanines nanoparticles: Synthesis, photoinduced intramolecular energy transfer and DNA interaction

Two series of fluorinated and non-fluorinated dendritic silicon (IV) phthalocyanines with cyano/nitro/ester terminal functionalities have been synthesized. Their structures were characterized by elemental analysis, FT-IR, 1H NMR and ESI-MS. The effects of fluorinated groups and terminal functionalities properties on the photophysical properties, photoinduced intermolecular electron transfer and intramolecular energy transfer of silicon phthalocyanines were compared. In order to endow water soluble and biocompatibility to these silicon phthalocyanines, an amphiphilic diblock copolymer polyethylene glycol monomethyl ether–polycaprolactone was used to encapsulate these silicon phthalocyanines to form fluorinated and non-fluorinated dendritic silicon phthalocyanines nanoparticles. The binding model between the fluorinated dendritic silicon phthalocyanines nanoparticles and calf thymus DNA was studied by UV–Vis and fluorescence spectroscopic method. The photocleavage DNA activities of three fluorinated dendritic silicon phthalocyanines nanoparticles were compared and the possible cleavage mechanism was proposed.