Anthryl-Appended Platinum(II) Schiff Base Complexes: Exceptionally Small Stokes Shift, Triplet Excited States Equilibrium, and Application in Triplet-Triplet-Annihilation Upconversion.

Two anthryl platinum(II) N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-benzenediamine Schiff base complexes were synthesized, with the anthryl attached via its 9 position (Pt-9An) or 2 position (Pt-2An) to the platinum (Pt) Schiff base backbone. The complexes show unusually small Stokes shifts (0.23 eV), representing a very small energy loss for the photoexcitation/intersystem crossing process, which is beneficial for applications as triplet photosensitizers. Phosphorescence of the Pt(II) coordination framework (ΦP = 11.0%) is quenched in the anthryl-containing complexes (ΦP = 4.0%) and shows a biexponential decay (τP = 3.4 µs/87% and 18.2 µs/13%) compared to the single-exponential decay of the native Pt(II) Schiff base complex (τP = 3.7 µs). Femtosecond/nanosecond transient absorption spectroscopy suggests an equilibrium between triplet anthracene (3An) and triplet metal-to-ligand charge-transfer (3MLCT) states, with the dark 3An state slightly lower in energy (1.96 eV for Pt-9An and 1.90 eV for Pt-2An) than the emissive 3MLCT state (1.97 eV for Pt-9An and 1.91 eV for Pt-2An). Intramolecular triplet-triplet energy transfer (TTET) and reverse TTET take 4.8 ps/444 ps for Pt-9An and 55 ps/1.7 ns for Pt-2An, respectively. The triplet-state equilibrium extends the triplet-state lifetime of the complexes to 103 µs (Pt-2An) or 163 µs (Pt-9An), in comparison to the native Pt(II) complex, which shows a lifetime of 4.0 µs. The complexes were used for triplet-triplet-annihilation upconversion with perylene as the triplet acceptor. The upconversion quantum yield is up to 15%, and a large anti-Stokes shift (0.75 eV) is achieved by excitation into the singlet metal-to-ligand charge-transfer absorption band (589 nm) of the complexes (anti-Stokes shift is 0.92 eV with 9,10-diphenylanthracene as the acceptor).

Intersystem Crossing in Naphthalenediimide-Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties.

Oxoverdazyl (Vz) radical units were covalently linked to the naphthalenediimide (NDI) chromophore to study the effect of the radical on the photophysical properties, especially the radical enhanced intersystem crossing (REISC), which is a promising approach to develop heavy-atom-free triplet photosensitizers. Rigid phenyl or ethynylphenyl linkers between the two moieties were used, thus REISC and formation of doublet (D1 , total spin quantum number S=1/2) and quartet states (Q1 , S=3/2) are anticipated. The photophysical properties of the dyads were studied with steady-state and femtosecond/nanosecond transient absorption (TA) spectroscopies and DFT computations. Femtosecond transient absorption spectra show a fast electron transfer (<150 fs), and ISC (ca. 1.4-1.85 ps) is induced by charge recombination (CR, in toluene). Nanosecond transient absorption spectra demonstrated a biexponential decay of the triplet state of the NDI moiety. The fast component (lifetime: 50 ns; population ratio: 80 %) is assigned to the D1 →D0 decay, and the slow decay component (2.0 µs; 20 %) to the Q1 →D0 ISC. DFT computations indicated ferromagnetic interactions between the radical and chromophore (J=0.07-0.13 eV). Reversible formation of the radical anion of the NDI moiety by photoreduction of the radical-NDI dyads in the presence of sacrificial electron donor triethanolamine (TEOA) is achieved. This work is useful for design of new triplet photosensitizers based on the REISC effect.

Efficient Radical-Enhanced Intersystem Crossing in an NDI-TEMPO Dyad: Photophysics, Electron Spin Polarization, and Application in Photodynamic Therapy.

A compact naphthalenediimide (NDI)-2,2,6,6-tetramethylpiperidinyloxy (TEMPO) dyad has been prepared with the aim of studying radical-enhanced intersystem crossing (EISC) and the formation of high spin states as well as electron spin polarization (ESP) dynamics. Compared with the previously reported radical-chromophore dyads, the present system shows a very high triplet state quantum yield (ΦT =74 %), a long-lived triplet state (τT =8.7 µs), fast EISC (1/kEISC =338 ps), and absorption in the red spectral region. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy showed that, upon photoexcitation in fluid solution at room temperature, the D0 state of the TEMPO moiety produces strong emissive (E) polarization owing to the quenching of the excited singlet state of NDI by the radical moiety (electron exchange J>0). The emissive polarization then inverts into absorptive (A) polarization within about 3 µs, and then relaxes to a thermal equilibrium while quenching the triplet state of NDI. The formation and decay of the quartet state were also observed. The dyad was used as a three-spin triplet photosensitizer for triplet-triplet annihilation upconversion (quantum yield ΦUC =2.6 %). Remarkably, when encapsulated into liposomes, the red-light-absorbing dyad-liposomes show good biocompatibility and excellent photodynamic therapy efficiency (phototoxicity EC50 =3.22 µm), and therefore is a promising candidate for future less toxic and multifunctional photodynamic therapeutic reagents.

Effect of thiophene substitution on the intersystem crossing of arene photosensitizers.

The effect of thienyl substitution on the intersystem crossing (ISC) of a few arenes was studied using steady state and time-resolved transient absorption and emission spectroscopies, as well as DFT/TDDFT computations. We found that the phenyl and thienyl substituents generally induce red-shifted absorptions for the chromophores, and the DFT/TDDFT computations show that the red-shifted absorption and emission are due to the increased HOMO and the reduced LUMO energy levels. Nanosecond transient absorption spectra indicate the formation of a triplet state, the triplet state lifetime is up to 282 µs, and the singlet oxygen quantum yields (ΦΔ) are up to 60%. DFT/TDDFT computations indicate that introducing the thienyl substituent alters the relative singlet/triplet excited state energy levels, and the energy level-matched S1/T2 states are responsible for the enhanced ISC of the thienyl compounds. This information is useful for the design of heavy atom-free triplet photosensitizers and for the study of the fundamental photochemistry of organic compounds.

Intramolecular Energy and Electron Transfers in Bodipy Naphthalenediimide Triads.

Borondipyrromethene (BDP) naphthalenediimide (NDI) triads (BDP-NDI) and diiodo-BDP derivative (DiiodoBDP-NDI)) were synthesized to study the Förster resonance energy transfer (FRET) and its impact on the triplet state formation and dynamics. In these triads, diiodo-BDP and BDP are the energy donors and NDI is the energy acceptor. Nanosecond transient absorption spectra of triads indicated that triplet state is localized on NDI moiety, either by selective photoexcitation of the Diiodo-BDP or NDI unit. The intersystem crossing (ISC) is attributed to intramolecular heavy atom effect. The triplet state quantum yield was found to be 54% with a lifetime of 38 µs. However, no triplet state is observed for BDP-NDI system either by exciting BDP or NDI unit. Thus, we confirmed that charge recombination does not produce a triplet state. Interestingly, DiiodoBDP-NDI can be used as broadband excitable (500-620 nm) triplet photosensitizer, and high triplet-triplet annihilation (TTA) upconversion quantum yield of ΦUC = 2.8% was observed with 9,10-bis(phenylethynyl)-anthracene (BPEA) as a triplet acceptor/emitter.

LP1 from Lentinula edodes C91-3 Induces Autophagy, Apoptosis and Reduces Metastasis in Human Gastric Cancer Cell Line SGC-7901.

Present study aimed to elucidate the anticancer effect and the possible molecular mechanism underlying the action of Latcripin 1 (LP1), from the mushroom Lentinula edodes strain C91-3 against gastric cancer cell lines SGC-7901 and BGC-823. Cell viability was measured by Cell Counting Kit-8 (CCK-8); morphological changes were observed by phase contrast microscope; autophagy was determined by transmission electron microscope and fluorescence microscope. Apoptosis and cell cycle were assessed by flow cytometer; wound-healing, transwell migration and invasion assays were performed to investigate the effect of LP1 on gastric cancer cell's migration and invasion. Herein, we found that LP1 resulted in the induction of autophagy by the formation of autophagosomes and conversion of light chain 3 (LC3I into LC3II. LP1 up-regulated the expression level of autophagy-related gene (Atg7, Atg5, Atg12, Atg14) and Beclin1; increased and decreased the expression level of pro-apoptotic (Bax) and anti-apoptotic (Bcl-2) proteins respectively, along with the activation of Caspase-3. At lower-doses, LP1 have shown to arrest cells in the S phase of the cell cycle and decreased the expression level of matrix metalloproteinase MMP-2 and MMP-9. In addition, it has also been shown to regulate the phosphorylation of one of the most hampered gastric cancer pathway, that is, protein kinase B/mammalian target of rapamycin (Akt/mTOR) channel and resulted in cell death. These findings suggested LP1 as a potential natural anti-cancer agent, for exploring the gastric cancer therapies and as a contender for further in vitro and in vivo investigations.

Preliminary evaluation of antimicrobial activity of cream formulated with essential oil of Trachyuspermum ammi.

In our present research we studied physiochemical properties and antimicrobial activity of T. ammi (Trachyuspermum ammi) seeds. The seeds yielded 2.86% essential oil. Refractive index, specific gravity, acid value, and easter values were 1.496, 0.9212, 1.12 and 2.80 respectively. GLC was used to determine the composition of oil. The major component of oil was Thymol (55.308%). Antimicrobial activity of the oil was carried out against four species of bacteria and fungs. The oil was used to formulate a cream and the pH, physiochemical stability, phase separation and dermal irritation of cream were investigated. The cream was examined for healing wound in rabbits in comparison with Iodine tincture.

Sodium alkoxide-mediated g-C3N4 immobilized on a composite nanofibrous membrane for preferable photocatalytic activity.

g-C3N4 is a classic photocatalyst not only owing to the metal-free semiconducting electronic structure but also tunable multifunctional properties. However, strategies for chemical exfoliation of g-C3N4 based on organic bases have been rarely reported. A family of sodium alkoxide-mediated g-C3N4 has been prepared via a simple synthesis. The degradation rate of bulk g-C3N4 is 39.8% when irradiation lasts 140 minutes. However, the degradation rate of g-C3N4-MeONa, g-C3N4-EtONa, and g-C3N4- t BuONa is 55.1%, 68.6%, and 79.1%, respectively, under the same conditions. Furthermore, g-C3N4- t BuONa has been immobilized on flexible electrospun PAN nanofibers to prepare floating photocatalysts. SEM analysis shows that the paper-based photocatalyst PAN/g-C3N4- t BuONa becomes a nanofiber membrane (A4 size, 210 mm × 297 mm). The nanofiber is approximately 350 nm in diameter. Interestingly, once synthesized, the g-C3N4- t BuONa particles move into the spinning solution, where the nanofiber wraps around them to form a monodisperse structure that resembles beads, or knots of 1-2 µm, on a string. The degradation efficiency of 10 mg L-1 MB solution can reach 100% for 2 hours until the solution becomes colorless. In addition, the photocatalytic mechanism studies have been validated. Different from H2SO4 or HNO3, this work has proposed a facile strategy for designing preferable floating photocatalysts using sodium alkoxide.

Spin-Orbit Charge-Transfer Intersystem Crossing of Compact Naphthalenediimide-Carbazole Electron-Donor-Acceptor Triads.

Compact electron donor-acceptor triads based on carbazole (Cz) and naphthalenediimide (NDI) were prepared to study the spin-orbit charge-transfer intersystem crossing (SOCT-ISC). By variation of the molecular conformation and electron-donating ability of the carbazole moieties, the electronic coupling between the two units was tuned, and as a result charge-transfer (CT) absorption bands with different magnitudes were observed (ε = 4000-18 000 M-1 cm-1). Interestingly, the triads with NDI attached at the 3-C position or with a phenyl spacer at the N position of the Cz moiety, thermally activated delayed fluorescence (TADF) was observed. Femtosecond transient absorption (fs-TA) spectroscopy indicated fast electron transfer (0.8-1.5 ps) from the Cz to NDI unit, followed by population of the triplet state (150-600 ps). Long-lived triplet states (up to τT = 45-50 µs) were observed for the triads. The solvent-polarity-dependent singlet-oxygen quantum yield (ΦΔ) is 0-26%. Time-resolved electron paramagnetic resonance (TREPR) spectral study of TADF molecules indicated the presence of the 3CT state for NDI-Cz-Ph (zero-field-splitting parameter D = 21 G) and an 3LE state for NDI-Ph-Cz (D = 586 G). The triads were used as triplet photosensitizers in triplet-triplet annihilation upconversion by excitation into the CT absorption band; the upconversion quantum yield was ΦUC = 8.2%, and there was a large anti-Stokes shift of 0.55 eV. Spatially confined photoexcitation is achieved with the upconversion using focusing laser beam excitation, and not the normally used collimated laser beam, i.e., the upconversion was only observed at the focal point of the laser beam. Photo-driven intermolecular electron transfer was demonstrated with reversible formation of the NDI-• radical anion in the presence of the sacrificial electron donor triethanolamine.