Photoinduced Charge-transfer Complexes Research Articles

Organocatalyzed iodine-mediated reversible-deactivation radical polymerization via photoinduced charge transfer complex catalysis

Organocatalyzed iodine-mediated reversible-deactivation radical polymerization via photoinduced charge transfer complex catalysis

Trapping highly reactive photoinduced charge-transfer complex between amine and imide by light

Trapping highly reactive photoinduced charge-transfer complex between amine and imide by light

Charge Transfer Complex-Enabled Synthesis of (Hetero)arylated m-Carboranes from m-Carborane Phosphonium Salts.

A photoinduced charge transfer complex (CTC)-enabled photoreduction of carborane phosphonium salts for the cage carbon (hetero)arylation of carboranes was developed. It offers a convenient approach for introducing a wide range of aryl and heteroaryl groups, such as pyrroles, thiophenes, indoles, thianaphthenes, benzofurans, pyridines, and benzenes, into carboranes. This strategy offers operational simplicity, mild reaction conditions, and a broad substrate scope, making it highly advantageous.

A visible-light photoinduced charge-transfer complex promoted the ring opening of N-alkyl-4-piperidinols

(E)-Homoallylamines are efficiently prepared through visible-light photoinduced charge-transfer complex promoted ring-opening of N-alkyl-4-piperidinols.

A DFT and TDDFT investigation of interactions between pyrene and amino acids with cyclic side chains

A computational investigation of photoinduced charge transfer complex formation between pyrene (Py) and amino acids with cyclic side chains (Phenylalanine: Phe, Tyrosine: Tyr, Tryptophan: Trp, Histidine, His) has been carried out in gas phase and in water. Geometry optimizations were performed by density functional theory (DFT) at ωB97XD/6-311++G(d,p) level. Time-dependent density functional theory (TDDFT) was used to calculate the electronic transitions of molecules at B3LYP/6-311++G(d,p) level using the above ground-state geometries. Polarizable Continuum Model (PCM) and SMD are used for calculations in water. Analyses and comparisons have been performed for total electronic energies, complexation energies, free energy differences, solvation energies, excitation wavelengths, and HOMO–LUMO energy gaps of complexes in gas phase and in solution. The intermolecular distances between Py and amino acids increased in water compared to the gas phase for all studied with the exception of Py–Tyr system. The optimized complexes display an increasing complex stability in the order Trp>Tyr>Phe>His. Analyses of first excited singlet states have indicated charge transfers transitions between Py and amino acids His and Trp through π–π stacking in gas phase at 345nm and 393nm, respectively. Py–Trp system has also charge transfer (CT) in water at 389nm. Py–Trp systems have the most significant charge transfer between HOMO and LUMO (full CT, 70%). However, S0–S1 transition (393nm) has weaker dipole moment and oscillator strength than the other studied systems. Due to its charge transfer character, Py–Trp systems seem to be appropriate models to investigate and design bioorganic photosensitive materials.

A DFT and TDDFT investigation of interactions between 1-hydroxypyrene and aromatic amino acids

This study presents a computational investigation of formation photoinduced charge transfer complexes between 1-hydroxypyrene (PyOH) and aromatic amino acids (Phenylalanine: Phe, Tyrosine: Tyr, Tryptophan: Trp) in gas phase and in water. Geometry optimizations were performed by density functional theory (DFT) at ωB97XD/6-311++G(d,p) level. Time-dependent density functional theory (TDDFT) was used to calculate the electronic transitions of molecules at B3LYP/6-311++G(d,p) and CAM-B3LYP/6-311++G(d,p) levels using the ground-state geometries from ωB97XD/6-311++G(d,p). Polarizable Continuum Model (PCM) is used for calculations in water. Total electronic energies, complexation energies, free energy differences, solvation energies, excitation wavelengths, and HOMO–LUMO energy gaps of complexes have been analyzed and compared in gas phase and in solution. The intermolecular distances between PyOH and amino acids increased in water compared to the gas phase. The optimized complexes display an increasing complex stability in the order Trp>Tyr>Phe. Analyses of first excited singlet states have revealed that there are charge transfers between PyOH and amino acids through π–π stacking except PyOH–Phe complexes in both media. The charge distributions increased in water. Among all studied systems, PyOH–Trp systems have the most significant charge transfer between HOMO−1 and LUMO (full CT, 59%). However, dipole moment and oscillator strength of this transition (S0–S1) are weaker compared to the other studied systems. PyOH–Trp systems are determined to be the best model to investigate and design bioorganic photosensitive materials with its charge transfer character.

(Invited) DAN Assisted Formation of Charge Transfer Complex from Highly Charged Fullerenes and Conjugated Polymer

Water-soluble, same charged, cationic conjugated poly(phenylenevinylene) (PPV) and cationic fullerenes were complexed with negatively charged single stranded DNA and double stranded DNA via electrostatic and pi-pi interactions. The photoinduced charge transfer complex (PPV/DNA/C60) has a charge transfer and separation efficiencies at least comparable to those observed from oppositely charged, cationic PPV and anionic fullerene. DNA serves as a template that straightens the PPV chain conformation which leads to an enhanced quantum yield. Meanwhile, DNA allows incorporation of C60 by overcoming the electrostatic repulsion between PPV and C60. While oppositely charge donor and acceptor molecules feature charge transfer in the form of static quenching, for DNA-assisted charge transfer complexes, the charge transfer proceeds as a combination of static and dynamic quenching for ssDNA and purely dynamic for dsDNA.

Direct detection of photoinduced charge transfer complexes in polymer fullerene blends

We report transient electron paramagnetic resonance (trEPR) measurements with sub-microsecond time resolution performed on a P3HT:PCBM blend at low temperature. The trEPR spectrum immediately following photoexcitation reveals signatures of spin-correlated polaron pairs. The pair partners (positive polarons in P3HT and negative polarons in PCBM) can be identified by their characteristic g-values. The fact that the polaron pair states exhibit strong non-Boltzmann population unambiguously shows that the constituents of each pair are geminate, i.e. originate from one exciton. We demonstrate that coupled polaron pairs are present even several microseconds after charge transfer and suggest that they embody the intermediate charge transfer complexes which form at the donor/acceptor interface and mediate the conversion from excitons into free charge carriers.

Photo-induced charge-transfer complex formation and organogelation by a tripeptide

A terminally protected tripeptide Boc–Phe–Phe–Tyr–OMe 1 and picric acid form a photo induced charge-transfer complex and organogels. The interactions between stacked aromatic units play a key role in the assembly process. UV light (366 nm) has been used as a source of energy to cleave and homogenize π-stacking in the supramolecular arrangement of peptide 1 and picric acid. CD, FT-IR, NMR and powder X-ray diffraction studies exhibit distinct structural changes before and after light irradiation. Field emission scanning electron microscopy of the xerogels reveal a morphological change caused by photo induced charge-transfer complex formation. The fluorescence spectroscopy as well as confocal microscopy studies show that these charge-transfer complexes have a significant red emission at 672 nm.

Detailed studies on the photoswitching property of ferrocene-doped poly(methyl methacrylate) thin films containing chloroform molecules

Electrical conductivity in solution cast (using chloroform as well as mixture of chloroform and benzene as solvents) ferrocene-doped poly(methyl methacrylate) (PMMA) thin films were studied under photoexcitation in air by using surface-type sample cells at room temperature (300 K). The changes in current were measured in the films upon photoexcitation and after turning it off for repeated photoexcitations after a sufficient interval of time. Such studies were carried out as a function of the amount of chloroform in the PMMA film as well as the amount of ferrocene in the film prepared from chloroform. Ferrocene-doped PMMA thin films prepared from solution in chloroform and modified under photoexcitation in air have exhibited interesting photoswitching property monitored by photoconductivity measurements in air. The rise and decay of the photocurrent were studied. The results on photoconductivity have been discussed on the basis of formation of photoinduced charge-transfer complexes of ferrocene with chloroform molecules confined in the PMMA thin films, dissociation of the complexes, secondary thermal reaction and photodegradation of PMMA. Photodegradation of PMMA was studied by FTIR spectroscopy. The possible application of the modified ferrocene-doped PMMA films (containing chloroform molecules) upon photoexcitation in air has been mentioned.

Absorption and fluorescence spectroscopic characterization of BLUF domain of AppA from Rhodobacter sphaeroides

The BLUF domain of the transcriptional anti-repressor protein AppA from the non-sulfur anoxyphototrophic purple bacterium Rhodobacter sphaeroides was characterized by absorption and emission spectroscopy. The BLUF domain constructs AppA 148 (consisting of amino-acid residues 1–148) and AppA 126 (amino-acid residues 1–126) are investigated. The cofactor of the investigated domains is found to consist of a mixture of the flavins riboflavin, FMN, and FAD. The dark-adapted domains exist in two different active receptor conformations (receptor states) with different sub-nanosecond fluorescence lifetimes (BLUF r,f and BLUF r,sl) and a small non-interacting conformation (BLUF nc). The active receptor conformations are transformed to putative signalling states (BLUF s,f and BLUF s,sl) of low fluorescence efficiency and picosecond fluorescence lifetime by blue-light excitation (light-adapted domains). In the dark at room temperature both signalling states recover back to the initial receptor states with a time constant of about 17 min. A quantum yield of signalling state formation of about 25% was determined by intensity dependent transmission measurements. A photo-cycle scheme is presented including photo-induced charge transfer complex formation, charge recombination, and protein binding pocket reorganisation.

Photoswitching Property of Ferrocene-doped Poly(methyl methacrylate) Thin Films Containing Chloroform Molecules

Abstract Ferrocene-doped poly(methyl methacrylate) (PMMA) thin films prepared from solution in chloroform and modified under photoexcitation have exhibited interesting photoswitching property monitored by photoconductivity measurements in air. The results on photoconductivity have been discussed on the basis of formation of photoinduced charge-transfer complexes of ferrocene with chloroform molecules confined in PMMA thin films, dissociation of the complexes, secondary thermal reaction and photodegradation of PMMA. Photodegradation of PMMA, was studied by FTIR spectroscopy. The modified ferrocene-doped PMMA films could be used as photoswitching elements.

The micellization of the diblock copolymer of ethylene oxide and styrene in benzene and the effect on the preparation of the star ABC triblock copolymer of ethylene oxide, styrene and methyl methacrylate

In the preparation of the ABC star triblock copolymer of ethylene oxide, styrene and methyl methacrylate (MMA), the photo-induced charge-transfer complex (CTC) was used to initiate the polymerization of the third monomer MMA. The CTC was composed of the diblock copolymer of poly(ethylene oxide) (PEO) and polystyrene (PS), PEO-bi-PS, with an aromatic imino group at the conjunction point and benzophenone (BP). It was confirmed that the kinetic behavior of this macromolecular initiation system is nearly the same with a general small radical initiator: the polymerization rate Rp ∝ [PEO-bi-PS]0.48[BP]0.45[MMA]0.97. Moreover, if the molecular weight of the PEO block is fixed, Rp is independent of the molecular weight of the PS block. By means of measurements of viscosity and fluorescence, it was found that the micelles of the diblock copolymer PEO-bi-PS were formed in benzene. The aromatic imino groups were located on the boundary surfaces of the micelles and were fully exposed, and so the BP and MMA molecules easily approached them and affected the charge-transfer polymerization of MMA.

Block Copolymerization of Ethylene Oxide and Styrene by Sequential Initiation of an Anion and a Photoinduced Charge Transfer Complex

A block copolymer composed of crystalline polyethylene oxide (PEO) and noncrystalline polystyrene (PS) was prepared by the combination of anion and photoinduced charge transfer polymerization (CTP) using p-aminophenol as the parent compound. The whole copolymerization was divided into two stages. In the first stage, the amino group of p-aminophenol was protected by benzaldehyde first and then reacted with metallic potassium. The phenoxy anion formed initiated polymerization of EO. In the second stage, the PEO prepolymer with the Schiffbase end group was deprotected by acidolysis with acetic acid. Then the recovered amino group and added benzophenone (BP) constituted a charge transfer complex (CTC) under UV irradiation to initiate the polymerization of styrene. The block copolymer of EO and St (PEO-b-PS) and the intermediates were characterized in detail by elemental analysis, GPC, UV, DSC, IR, and NMR.

Effects of iodine doping on the photoconductivity of polyvinyl chloride thin films

Surface photocurrent studies of thin films (thickness approximately 1500 Å) of iodine-doped polyvinyl chloride (PVC-I 2) were made as a function of the applied field, with an iodine concentration of 0.2–1.0 g per 100 ml PVC solution. Initially the photoconductivity increases with increasing concentration of iodine. This trend continues up to a weight ratio of 3:3.5 of PVC to iodine. Beyond this concentration there is a continuous decrease in the photoconduction. The initial increase in photoconductivity for lower concentrations (PVC:I 2 weight ratios of 3:3.5 or less) is interpreted on the basis of the formation of photoinduced charge transfer complexes in the film. The decrease in photoconductivity for higher concentrations (PVC:I 2 weight ratios greater than 3:3.5) is ascribed to the reduced mobility of charge carriers owing to space charge.