Lifetime Of Singlet State Research Articles

Synthesis, Structure, Spectral and Electrochemical Properties of 5,6,7,9,10,11‐Hexaaryl Substituted Meso‐(p‐Tolyl) 3‐Pyrrolyl BODIPYs

Hexabrominated meso‐(p‐tolyl) 3‐pyrrolyl BODIPY was regioselectively synthesized by treating meso‐(p‐tolyl) 3‐pyrrolyl BODIPY with eight equivalents of Br2 in CH2Cl2 under inert atmosphere at room temperature. Five different 5,6,7,9,10,11‐hexaarylated meso‐(p‐tolyl) 3‐pyrrolyl BODIPYs were synthesized by treating 5,6,7,9,10,11‐hexabromo meso‐(p‐tolyl) 3‐pyrrolyl BODIPY with various boronic acids under Suzuki coupling conditions. The X‐ray structure obtained for hexabromo and hexaarylated 3‐pyrrolyl BODIPYs showed slightly distorted structures. Absorption spectral studies revealed that the absorption bands in hexabromo and hexaarylated 3‐pyrrolyl BODIPYs were bathochromically shifted compared to 3‐pyrrolyl BODIPY. The hexabromo 3‐pyrrolyl BODIPY was less fluorescent due to presence of heavy halogens whereas the hexaarylated 3‐pyrrolyl BODIPYs emits moderately in the region of 687‐736 nm with quantum yields in the range of 0.18‐0.30 and singlet state lifetimes in 2.99‐4.50 ns range. The electrochemical studies revealed that hexabrominated 3‐pyrrolyl BODIPY undergo easier reduction compared to 3‐pyrrolyl BODIPY. The hexaarylated 3‐pyrrolyl BODIPYs showed one reversible/quasi‐reversible oxidation and one reversible reduction and their redox behaviour depends on the type of electron donating or electron withdrawing substituents present at the pyrrole carbons. DFT/TD‐DFT studies were in agreement with the experimental results.

Synthesis and Properties of Tris(3‐Pyrrolyl BODIPY) on 1, 3, 5‐Triazine Scaffold

AbstractTris(3‐pyrrolyl BODIPY) on 1,3,5‐triazine scaffold was synthesized over a sequence of steps starting from commercially available cyanuric chloride. The cyanuric chloride was reacted with p‐hydroxy benzaldehyde to afford 1,3,5‐triazine tris(p‐oxybenzaldehyde) which was then reacted with excess pyrrole under acid catalyzed conditions to afford 1,3,5‐triazine‐tris(meso‐p‐oxyphenyl dipyrromethane). Subsequent in situ oxidation of this compound with DDQ to obtain tris(meso‐oxyphenyldipyrromethene) which was then treated with pyrrole followed by the addition of Et3N/BF3 ⋅ OEt2 afforded fluorescent tris(3‐pyrrolyl BODIPY). For comparison, tris(BODIPY) on the triazine scaffold was prepared by oxidizing tris(meso‐oxyphenyldipyrromethane) with DDQ followed by complexation with BF3 ⋅ OEt2. Both compounds were thoroughly characterized and studied by various experimental and theoretical methods. Absorption, steady state fluorescence, time‐resolved fluorescence, and transient‐absorption studies revealed that in tris(3‐pyrrolyl BODIPY), excitonic interactions between two of the three 3‐pyrrolyl BODIPY units resulted in a hypsochromic shift in spectral bands, reducing the quantum yield and singlet state lifetime whereas tris(BODIPY) did not show such excitonic interactions. DFT studies helped in understanding the excitonic interactions in tris(3‐pyrrolyl BODIPY). The tris(3‐pyrrolyl BODIPY) was fluorescent both in solution and solid state. The viscosity studies indicated that the fluorescence of tris(3‐pyrrolyl BODIPY) increases significantly with solvent viscosity, suggesting its potential for measuring cellular viscosity during physiological processes.

Presenting a new fluorescent probe, methyl(10-phenylphenanthren-9-yl)sulfane sensitive to the polarity and rigidity of the microenvironment: applications toward microheterogeneous systems.

A molecule, methyl(10-phenylphenanthren-9-yl)sulfane (MPPS), with a straightforward structure, has been synthesized, characterized, and explored as a new fluorescent probe for microheterogeneous systems. The photophysical properties of MPPS have been studied through experimental and theoretical calculations using the range-separated hybrid functional CAM-B3LYP in conjunction with a 6-311++g(d,p) basis set. Theoretical calculations show that the freely rotating phenyl ring forms a 94° dihedral angle with the phenanthrene ring in the ground state. Experimentally found two absorption bands correspond to the n → π* and π → π* transitions supported by the frontier molecular orbital calculations. Two excited singlet states, E-1 and E-2 (the former being more stable than the latter in the gas phase), exist with dihedral angles between the phenyl and phenanthrene rings as 142° and 133°, respectively, in the gas phase. Two emitting states in a condensed medium of varying polarities are supported by the steady-state fluorescence and fluorescence intensity decay data. Emission energies, fluorescence intensities, and excited singlet state lifetimes change with the polarity of the solvents. To support that the free rotation in the molecule is responsible for these changes, the fluorescence properties of another molecule, methyl(10-(o-tolyl)phenanthren-9-yl)sulfane (MTPS), with restricted rotation of the substituted benzene, i.e., o-tolyl ring have been studied. The fast-intensity decay component of MPPS is ascribed to the conformer in the E-1 state. The molecule has proved to be an excellent polarity probe explored to determine the critical micelle concentrations (cmc) values of different surfactants, which agree well with the literature reports. Different regions of binding isotherm (specific, non-cooperative, cooperative, and massive binding) of a gemini surfactant, 12-6-12,2Br- with bovine serum albumin (BSA) have been successfully demonstrated by the steady-state and time-resolved fluorescence and fluorescence anisotropic properties of MPPS. Docking results show that MPPS resides in the hydrophobic pocket of BSA. The fluorescence quenching of BSA by MPPS reveals the location of Trp residues of BSA. Thus, a polarity and molecular rigidity-sensitive fluorescent molecule, MPPS has been presented here that can potentially be used to monitor the changes in the microenvironment of biomolecules in different processes.

Advancing Organic Photoredox Catalysis: Mechanistic Insight through Time-Resolved Spectroscopy.

The rapid development of light-activated organic photoredox catalysts has led to the proliferation of powerful synthetic chemical strategies with industrial and pharmaceutical applications. Despite the advancement in synthetic approaches, a detailed understanding of the mechanisms governing these reactions has lagged. Time-resolved optical spectroscopy provides a method to track organic photoredox catalysis processes and reveal the energy pathways that drive reaction mechanisms. These measurements are sensitive to key processes in organic photoredox catalysis such as charge or energy transfer, lifetimes of singlet or triplet states, and solvation dynamics. The sensitivity and specificity of ultrafast spectroscopic measurements can provide a new perspective on the mechanisms of these reactions, including electron-transfer events, the role of solvent, and the short lifetimes of radical intermediates.

Modulation of lanthanide luminescence by carbamoylmethylphosphine oxide ligand: A theoretical study

The antenna capacity of Phenacyldiphenylphosphine oxide (Phenac), combining C=O and P=O donor groups was established by theoretical examination of its chromophore properties, binding ability to encapsulate and stabilize lanthanide complexes and potential to sensitize the EuIII and TbIII luminescence in Eu(Phenac)2(NO3)3(H2O) (1), Eu(Phenac)2(NO3)3 (2), Eu(Phenac)3(NO3)3 (3) and Tb(Phenac)2(NO3)3(H2O) (4) complexes in vacuum, solution and solid phase. The ligand-centered singlet and triplet excited state energies, the rates and lifetimes for the rival nonradiative (S1→T1,2 intersystem crossing (ISC)) and radiative and nonradiative S1→S0 and T1→S0 relaxation were predicted by means of DFT/TDDFT/ωB97XD calculations. Similar relaxation paths were found for all complexes. The absorbed energy by Sn > 1(π-π*) states relaxed to T1min by major ISC mechanism S1→T2→T1. The long radiative lifetime of S1→S0 due to n(p(C)(O))π-π*,p(P) character facilitated the forward ISC process. The environment, Phenac's number and LnIII size affect the T1 energy ∼0.1 eV. The calculated (Phenac→EuIII) energy transfer rates suggested the most likely T1 → 5D1/5D0 channels for a population of emitting metal-centered states. The small Φ of EuIII and larger luminescence of TbIII were discussed and explained. The importance of the P=O and C=O groups for the coordination ability and absorption properties of Phenac has been elucidated.

Counterdiabatic driving for long-lived singlet state preparation.

The quantum adiabatic method, which maintains populations in their instantaneous eigenstates throughout the state evolution, is an established and often a preferred choice for state preparation and manipulation. Although it minimizes the driving cost significantly, its slow speed is a severe limitation in noisy intermediate-scale quantum era technologies. Since adiabatic paths are extensive in many physical processes, it is of broader interest to achieve adiabaticity at a much faster rate. Shortcuts to adiabaticity techniques, which overcome the slow adiabatic process by driving the system faster through non-adiabatic paths, have seen increased attention recently. The extraordinarily long lifetime of the long-lived singlet states (LLS) in nuclear magnetic resonance (NMR), established over the past decade, has opened several important applications ranging from spectroscopy to biomedical imaging. Various methods, including adiabatic methods, are already being used to prepare LLS. In this article, we report the use of counterdiabatic driving (CD) to speed up LLS preparation with faster drives. Using NMR experiments, we show that CD can give stronger LLS order in shorter durations than conventional adiabatic driving.

Toward efficient photochemistry from upper excited electronic states: Detection of long S2 lifetime of perylene.

A long 0.9ps lifetime of the upper excited singlet state in perylene is resolved by femtosecond pump-probe measurements under ultraviolet (4.96eV) excitation and further validated by theoretical simulations of transient absorption kinetics. This finding prompts exploration and development of novel perylene-based materials for upper excited state photochemistry applications.

Singlet and Triplet State Properties and Singlet Oxygen Yield of an Amino-Acyl-Quinoxalinone Yellow Dye.

Amino-acyl-quinoxalinone yellow dyes are cyclised analogues of the yellow azomethine dyes developed for, and still used in, silver halide colour photography. Unlike image azomethine dyes, which are rapidly deactivated in their excited states by torsion about the azomethine bond, amino-acyl-quinoxalinone dyes have an interesting photophysics because torsion is not possible due to their cyclised structure. We report results from studies on singlet and triplet state properties, and singlet oxygen yields, of the yellow dye, 7-diethylamino-3-(2,2-dimethyl-propionyl)-5-methyl-1-phenyl-1H-quinoxalin-2-one, in polar and nonpolar solvents. The dye photophysics is characterised by a weak fluorescence, with a solvent dependent emission yield (ΦF ≈ 0.002-0.004), and short singlet state lifetime (τexpt ≈ 20-50ps), both increasing by a factor of ≈2 in going from polar acetonitrile to non-polar dioxane as solvent. DFT ZINDO calculations show a transition involving significant electron transfer from the diethyl-amino group into the carbonyl region of the molecule. In solution, in the presence of oxygen, the triplet state decays almost exclusively by oxygen quenching, and singlet oxygen is produced in high yield (Φ∆ ≈ 0.5-0.55). The triplet state absorbs across the 450-750nm region with maxima around 480 and 650nm, and moderate molar absorption coefficients (ca. 6000-8000M-1cm-1). In a glass at 77K, triplet decay gives a red phosphorescence, with λmax ≈ 640-650nm, and a ≈ 0.25s lifetime. If singlet oxygen yields are a good indication of triplet yields, then internal conversion and intersystem crossing occur with roughly equal efficiency.

Fluorinated aluminum(III) porphyrins: Synthesis, spectroscopy, electrochemistry and photochemistry

A series of fluorinated free-base porphyrins (H2TPPF[Formula: see text], [Formula: see text] = 0, 8, 12, 20, 24) and the corresponding aluminum(III) porphyrin (AlTPPF[Formula: see text]-Ph, [Formula: see text] = 0, 8, 12, 20, 24) derivatives have been synthesized and their spectroscopic, redox and optical properties were investigated. The absorption studies show that the spectral shapes of investigated porphyrins are sensitive to the degree of fluorination on the meso-phenyl units. Analogously, the fluorescence quantum yields and singlet-state lifetimes depend on the number of fluorine atoms, and decrease by increasing the number of fluorine atoms. The H2TPPF[Formula: see text] and AlTPPF[Formula: see text]-Ph ([Formula: see text] = 8, 12, 20, 24) derivatives exhibited lower fluorescence intensities compared to the H2TPP and AlTPP, respectively. However, the AlTPPF[Formula: see text]-Ph ([Formula: see text] = 0, 8, 12, 20, 24) derivatives yield relatively a strong fluorescence compared to the well-known ZnTPP. As predicted, the redox potentials are shifted to the more positive side by increasing the fluorine atoms. The Lewis acidity of AlTPPF[Formula: see text]-Ph was quantified by using the absorption and fluorescence titrations with the Lewis base [Formula: see text]-methylimidazole (Me-Im). The titration data suggests that the Lewis acidity of the Al center rises when increasing the number of fluorine atoms on the porphyrin. Together, the high fluorescence quantum yields, high-potentials, unique optical and redox properties suggest that the investigated porphyrins could be potential sensitizers to mimic various components of artificial photosynthetic systems for the production of solar fuels.

Synthesis of 3H‐Pyrrolo‐(1,2‐a) Indole‐based Fluorophore Macrocycles and their Stable Cation Radicals

AbstractSmall molecular fluorophores with high quantum yields are of particular interest because of their role in several applications that range from ion sensing to bioimaging. Indole based biomolecules are well known for their fluorescence properties. Pyrrolo[1,2‐a]indoles have gained tremendous interest in recent times due to their applicability in various fields such as biomedicine and dye‐sensitized solar cells (DSSC). In this article, we report the synthesis of new types of crowned 3H‐pyrrolo[1,2‐a]indole fluorophore macrocycles 1–3 which were prepared in 30–35% yields using commercially available compounds under simple reaction conditions. These fluorophore macrocycles 1–3 were characterized by HR‐MS, 1D & 2D NMR, X‐ray crystallography, absorption, fluorescence, electrochemical, and DFT/TD‐DFT studies. The fluorophores 1–3 absorb in the region of 465–480 nm and emit in the region of 615–645 nm with large Stokes shift (∼150 nm), 10–20% quantum yields, and singlet state lifetimes of 1.70–2.50 ns. The electrochemical studies revealed that macrocycles 1–3 are electron‐rich and undergo easier oxidations. The macrocycles 1–3 readily form cation radicals by chemical and electrochemical oxidation which are highly stable at low temperatures as well as at room temperature.

Optical, Fluorescence Lifetime, Sensing and DNA Binding Studies of a Laser Dye

Herein, the effects of media on the fluorescence characteristics (mainly quantum yield, lifetime and radiationless deactivation rate of the excited singlet state) of phenylene-1,4-ethylene-bis-(2-quinoxaline) laser dye, BQxVB have been reported. Also, the sensitivity of the dye to the proton has been tested by studying the effect of changing the acidic properties of the medium. As with polarity, the acidity of solution provokes spectral changes. As the acidity of the medium increases (using H2SO4 solutions), the pale yellow color of BQxVB changes to orange then violet and eventually to deep blue in concentrated acid solutions. The effect of metallic and bimetallic nanoparticles on the spectral behavior of BQxVB dye has been investigated. Additionally, the binding of the dye by β-cyclodextrin was investigated. The capped and binding of the dye with CT-DNA were visualized based on the spectral studies. Finally, a molecular docking analysis was carried out on five chosen proteins, which are largely responsible for the formation of CT-DNA, 4ASD-transferase, 3UW9 protein binding, 3DDC–hydrolase/apoptosis, 3L8-transferase/CT-DNA, and 4ICH-transcription. Based on the results, it has been clearly shown that BQxVB shows better docking with the 4ASD-transferase protein than the other selected proteins, with an estimated binding Gibbs energy of − 50.45 kJ·mol−1, a total intermolecular energy of − 55.09 kJ·mol−1, an inhibition constant of 1.48 nmol·dm−3, and a binding efficiency of 80%.

Theoretical Investigation on Copper(I) Complexes Featuring a Phosphonic Acid Anchor with Asymmetric Ligands for DSSC

A series of heteroleptic copper­(I) complexes featuring a phosphonic acid anchor with asymmetric ligands has been studied using density functional theory (DFT) and time-dependent DFT (TD-DFT). Results showed that the absorption spectra of all copper­(I) complexes covered the visible light region with typical metal-to-ligand charge transfer characteristics. The modification of functionalized asymmetric ligands by introducing phenyl, anisole, N,N-diethyl-4-vinylaniline, and bromobenzene groups can reduce the energy gap (ΔH–L), form an effective charge-separated state, and lead to red-shifted absorption within the 350–650 nm range compared to the reference complex. The copper­(I) complexes with functionalized N,N-diethyl-4-vinylaniline ligands displayed the smallest ΔH–L and highest light-harvesting efficiency (LHE), exhibiting excellent light-harvesting capabilities. The introduction of isoquinoline ligands increased the excited singlet state lifetimes, the number of transferred electrons, and electron transfer distances. The electron injection time and driving force revealed efficient interfacial electron injection and regeneration of oxidized dyes. The photoelectronic properties of copper­(I) complexes featuring a pyridine ring with asymmetric ancillary ligands were superior to those of the reference complex. These copper­(I) complexes exhibited desirable electronic and spectral characteristics for future DSSC applications.

Redox Control Recombination in Axially Linked “Donor – Aluminum(III) Porphyrin – Fullerene” Reaction Center Models

Aluminum(III) porphyrins (AlPor) are well suited for the construction of axially linked multicomponent donor-acceptor systems. The axial hydroxide reacts with carboxylic acids or alcohols to form covalent ester or ether linkage, respectively. Moreover, they bind Lewis bases such as imidazole or pyridine to form a coordination bond with the Al center. They hold high fluorescence quantum yields with adequate singlet and triplet state lifetimes, as well as rich redox chemistry with two reversible oxidation and reduction processes. They can act as either a photosensitizing electron acceptor or donor with a wide variety of redox and optically active compounds. By exploiting these unique properties, we have designed several donor-AlPor-acceptor systems to mimic the reaction center complex of natural photosynthesis. In these systems, we have studied the electron transfer processes in perpendicular to the porphyrin plane. The optical studies showed that the excitation of AlPor results in a sequential electron transfer between redox-active units to generate long-lived radical pairs. I will discuss some of these systems to show how the recombination dynamics depend on the redox potentials.

Photo-physicochemical properties of water-soluble non-aggregated indium(III) phthalocyanines.

Phthalocyanines have interesting optoelectronic properties but typically suffer from aggregation in aqueous solution, which can limit their applicability, especially in photodynamic therapy. In this study, indium(III) phthalocyanine peripherally substituted with eight triazolyl-containing phenoxy groups (InOAc) and its water-soluble analogue (Q-InOAc) were synthesised and structurally characterised. Heavy metal effects, exerted by the central indium ion, on the photosensitising and photophysical properties (singlet oxygen quantum yield, singlet state lifetime and quantum yield, and triplet state lifetime) were investigated in both DMF and D2O. Highly efficient generation of the triplet excited state (T1), induced by the incorporation of a large atom, enhanced singlet oxygen formation, as revealed by both chemical and physical methods. Correspondingly, the singlet oxygen quantum yield (ΦΔ) of Q-InOAc was 0.603 in DMF and 0.433 in D2O. These values are higher than those previously reported for the corresponding metal-free, Mg-based, and Zn-based water-soluble phthalocyanines (HH, Mg, and Zn). Consequently, Q-InOAc is expected to be an excellent photosensitiser for photodynamic therapy.

The Effect of Cryo Temperature on Commonly used Fluorophores

Correlated cryo-fluorescence and cryo-electron microscopy (cryo-CLEM) has become an increasingly popular method for combining the resolving power of cryo-EM with the specificity of fluorescence. Although cryo-fluorescence microscopy suffers from optical limitations, it is a powerful way to target the resolving power of cryo-EM toward proteins of interest in heterogeneous cellular environments. Super-resolution microscopy at cryo temperatures has also been established using several different approaches. While fluorescence-derived localization is a key benefit of cryo-CLEM, fluorescence can also be used to bring orthogonal information into cryo-EM images. We recently developed a fusion assay compatible with cryo-CLEM equipment and conditions (Metskas and Briggs, Microscopy & Microanalysis 2019). This development employs auto-quenching by resonant energy transfer to specifically target a function rather than a protein in cryo-CLEM - in this case, adding information on lipid mixing to morphologies from micrographs of influenza virus fusion. However, further methods developments, particularly those involving FRET, are currently hampered by limited characterization of modern fluorophores at cryo-CLEM temperatures (77-100 K). Here, we present a study of commonly used synthetic fluorophores and fluorescent proteins, characterizing excitation and emission spectra, singlet state lifetime, and quantum yield at 77 K. We note that 10 nm shifts of the modes are common for both excitation and emission spectra, but are fluorophore specific in magnitude and even in direction. Vibronic coupling and spectral narrowing are visible in all cases characterized, and singlet state lifetimes increase or decrease in a fluorophore-specific manner. Taken together, these data suggest guidelines for choosing cryo-CLEM fluorophores and filter sets, and demonstrate promise for techniques such as FRET in carefully-adapted applications.

Framework induced deformation modulates the photophysical properties of ZnTetra(4-pyridyl)porphyrin incorporated within a new metal organic framework, RWLAA-1

Porphyrin based metal organic frameworks (MOFs) have provided a broad platform through which a wide variety of light harvesting applications have been developed. Of particular interest within light harvesting MOFs containing porphyrin chromophores is the extent to which the both environment of the porphyrin and the porphyrin conformation modulate the photophysical properties. With this in mind, a new MOF (RWLAA-1) has been synthesized based on zinc cations linked by zinc(ii) tetra(4-pyridyl)porphyrin (ZnTPyP) and benzene tricarboxylate (H3BTC) linkers in which the porphyrin exhibits significant conformational distortions that have a profound effect on the photophysics of the material including bathochromic shifts in both the optical (Soret and visible bands) and emission bands, reduction in the energy separation between the Q(0,0) and Q(0,1) emission bands and shorter singlet and triplet state lifetimes. These effects are consistent with the porphyrin deformation resulting in changes in the porphyrin electronic structure and excited state conformational dynamics that alter the vibronic coupling between the excited states (S1 and T1) and the S0 ground state.

Designing Sub-2 nm Organosilica Nanohybrids for Far-Field Super-Resolution Imaging.

Stimulated emission depletion (STED) microscopy enables ultrastructural imaging of biological samples with high spatiotemporal resolution. STED nanoprobes based on fluorescent organosilica nanohybrids featuring sub-2 nm size and near-unity quantum yield are presented. The spin-orbit coupling (SOC) of heavy-atom-rich organic fluorophores is mitigated through a silane-molecule-mediated condensation/dehalogenation process, resulting in bright fluorescent organosilica nanohybrids with multiple emitters in one hybrid nanodot. When harnessed as STED nanoprobes, these fluorescent nanohybrids show intense photoluminescence, high biocompatibility, and long-term photostability. Taking advantage of the low-power excitation (0.5 μW), prolonged singlet-state lifetime, and negligible depletion-induced re-excitation, these STED nanohybrids present high depletion efficiency (>96 %), extremely low saturation intensity (0.54 mW, ca. 0.188 MW cm-2 ), and ultra-high lateral resolution (ca. λem /28).

Kinetics of Enhancement for Corneal Cross-linking: Proposed Model for a Two-initiator System

Aims: To derive kinetic equations and analytic formulas for efficacy enhancement of corneal collagen crosslinking (CXL) in a 2-initiator system.
 Study Design: Modeling the kinetics of CXL.
 Place and Duration of Study: Taipei, Taiwan, between between January 2019 to June, 2019.
 Methodology: Coupled rate equations are derived for two initiators system for a type-II process, consisting of a primary initiator (PA), and a co-initiator (PB) as an enhancer, having 3 cross linking pathways: Two radical-mediated (or electron transfer) pathways, and one oxygen-mediated (or energy transfer) pathway. For a type-II process, the triplet state T* interacts with the co-initiator, PB, to form the primary radicals R’, and an active intermediates radical, R, which could interact with the substrate [M] for crosslink, or be inhibited by oxygen [O2], or bimolecular termination. Rate equations, based on lifetime of triplet-state and oxygen singlet-state, are used to analyze the measured results in a rose-Bengal system with an enhanced initiator.
 Results: Additive enhancer-monomer of arginine added to a rose Bengal photosensitizer may enhance the production of free radicals under a green-light CXL. D2O may extends the lifetime of oxygen singlet state and thus improve the efficacy. Our formulas predicted features are consistent with the measured results.
 Conclusion: Efficacy may be improved by enhancer-monomer or extended lifetime of photosensitizer triplet-state or oxygen singlet state.

Photophysics of BODIPY-Based Photosensitizer for Photodynamic Therapy: Surface Hopping and Classical Molecular Dynamics.

Halogenated BODIPY derivatives are emerging as important candidates for photodynamic therapy of cancer cells due to their high triplet quantum yield. We probed fundamental photophysical properties and interactions with biological environments of such photosensitizers. To this end, we employed static TD-DFT quantum chemical calculations as well as TD-DFT surface hopping molecular dynamics on potential energy surfaces resulting from the eigenstates of the total electronic Hamiltonian including the spin-orbit (SO) coupling. Matrix elements of an effective one-electron spin-orbit Hamiltonian between singlet and triplet configuration interaction singles (CIS) auxiliary wave functions are calculated using a new code capable of dealing with singlets and both restricted and unrestricted triplets built up from up to three different and independent sets of (singlet, alpha, and beta) molecular orbitals. The interaction with a biological environment was addressed by using classical molecular dynamics (MD) in a scheme that implicitly accounts for electronically excited states. For the surface hopping trajectories, an accelerated MD approach was used, in which the SO couplings are scaled up, to make the calculations computationally feasible, and the lifetimes are extrapolated back to unscaled SO couplings. The lifetime of the first excited singlet state estimated by semiclassical surface hopping simulations is 139 ± 75 ps. Classical MD demonstrates that halogenated BODIPY in the ground state, in contrast to the unsubstituted one, is stable in the headgroup region of minimalistic cell membrane models, and while in the triplet state, the molecule relocates to the membrane interior ready for further steps of photodynamic therapy.

Visible Light‐Mediated Conversion of Alcohols to Bromides by a Benzothiadiazole‐Containing Organic Photocatalyst

AbstractThe search for metal‐free, stable and high effective photocatalysts with sufficient photo‐redox potentials remains a key challenge for organic chemists. Here, we present a benzothiadiazole‐containing molecular organic photocatalyst with redox potentials of −1.30 V and +1.64 V vs. SCE. The singlet state lifetime is 13 ns. Direct conversion from aliphatic alcohols to bromides has been conducted with the designed organic photocatalyst under visible light irradiation with high efficiency and selectivity. The catalytic efficiency of the novel benzothiadiazole‐based photocatalyst is comparable with the state‐of‐art metal and non‐metal catalysts. Furthermore, advanced photophysical studies including time‐resolved photoluminescence and transient absorption spectroscopy offer a powerful support for photo‐induced electron transfer from photocatalyst to the reactive substrates. Lastly, no photo‐bleaching effect is observed, demonstrating the high stability and recyclable of the designed organic photocatalyst.magnified image