The ability to form triplet excited states upon two-photon excitation is important for several applications of metalloporphyrins, including two-photon phosphorescence lifetime microscopy (2PLM) and two-photon photodynamic therapy (PDT). Here we analyzed one-photon (1P) and degenerate two-photon (2P) absorption properties of several phosphorescent Pt (II) porphyrins, focusing on the effects of aromatic π-extension and peripheral substitution on triplet emissivity and two-photon absorption (2PA). Our 2PA measurements for the first time made use of direct time-resolved detection of phosphorescence, having the ability to efficiently reject laser background through microsecond time gating. π-Extension of the porphyrin macrocycle by way of syn-fusion with two external aromatic fragments, such as in syn-dibenzo- (DBP) and syn-dinaphthoporphyrins (DNP), lowers the symmetry of the porphyrin skeleton. As a result, DBPs and DNPs exhibit stronger 2PA into the one-photon-allowed B (Soret) and Q states than fully symmetric (D) nonextended porphyrins. However, much more 2P-active states lie above the B state and cannot be accessed due to the interfering linear absorption. Alkoxycarbonyl groups (COR) in the benzo-rings dramatically enhance 2PA near the B state level. Time-dependent density functional theory (TDDFT) calculations in combinations with the sum-over-states (SOS) formalism revealed that the enhancement is due to the stabilization of higher-lying 2P-active states, which are dominated by the excitations involving orbitals extending onto the carbonyl groups. Furthermore, calculations predicted even stronger stabilization of the 2P-allowed gerade-states in symmetric Pt octaalkoxycarbonyl-tetrabenzoporphyrins. Experiments confirmed that the 2PA cross-section of PtTBP(COBu) near 810 nm reaches above 500 GM in spite of its completely centrosymmetric structure. Combined with exceptionally bright phosphorescence (ϕ = 0.45), strong 2PA makes Pt(II) complexes of π-extended porphyrins a valuable class of chromophores for 2P applications. Another important advantage of these porphyrinoids is their compact size and easily scalable synthesis.

Actin bundles are key factors in the mechanical support and dynamic reorganization of the cytoskeleton. High concentrations of multivalent counterions promote bundle formation through electrostatic attraction between actin filaments that are negatively charged polyelectrolytes. In this study, we evaluate how physiologically relevant divalent cations affect the mechanical, dynamic, and structural properties of actin bundles. Using a combination of total internal reflection fluorescence microscopy, transmission electron microscopy, and dynamic light scattering, we demonstrate that divalent cations modulate bundle stiffness, length distribution, and lateral growth. Molecular dynamics simulations of an all-atom model of the actin bundle reveal specific actin residues coordinate cation-binding sites that promote the bundle formation. Our work suggests that specific cation interactions may play a fundamental role in the assembly, structure, and mechanical properties of actin bundles.

Using time-dependent density functional theory (TDDFT) and sum-overstates (SOS) formalism, we predicted significant stabilization of 2P-active g-states in a compact fully symmetric porphyrin, in which all four pyrrolic fragments are fused with phathalimide residues via the β-carbon positions. The synthesis of a soluble, nonaggregating meso-unsubstituted tetraarylphthalimidoporphyrin (TAPIP) was then developed, and the spectroscopic measurements confirmed that a strongly 2P-active state in this porphyrin is stabilized below the B (Soret) state level. Single-crystal X-ray analysis revealed near-ideally planar geometry of the TAPIP macrocycle, while its tetra-meso-arylated analogue (meso-ArTAPIP) was found to be highly saddled. Consistent with these structural features, Pt meso-ArTAPIP phosphoresces rather weakly (ϕ = 0.05 in DMF at 22 °C), while both Pt and Pd complexes of TAPIP are highly phosphorescent (ϕ = 0.45 and 0.23, respectively). In addition PdTAPIP exhibits non-negligible thermally activated (E-type) delayed fluorescence (ϕ(d) ∼ 0.012). Taken together, these photophysical properties make metal complexes of meso-unsubstituted tetaarylphthalimidoporphyrins the brightest 2P-absorbing phosphorescent chromophores known to date.

Three mixed-ligand Cu(II) complexes with compositions [Cu(phen) 2 (SO 4 )]·CH 3 OH (1), [Cu(phen) 2 (SO 4 )]-(H 2 O) 2 (dmf) (2), and [Cu(phen) 2 H 2 O](SO 4 )(H 2 O) 4 (3), where phen = 1,10-phenanthroline and dmf = N,N′-dimethylformamide, were prepared and studied. These compounds belong to the landscape of the mononuclear Cu(phen) 2 sulfates, and the solvated complexes undergo frequent anion/water exchange at the metal center in aqueous solutions. Complexes are similar by the metal trigonal bipyramidal coordination geometry but differ by the mode of enclathration and number of protic and aprotic solvent guest molecules being accommodated in the crystal lattice. Crystal packing in 1−3 is determined by the robust supramolecular patterns that consist of stacking interactions between the planar extended phen fragments. These are observed in all three solids regardless of the interplay of other noncovalent interactions, including rather strong hydrogen bonds. The dual luminescence is detected at 580 and 470 nm for both crystals of phen and 3. Detailed analysis of singlet and triplet excitations in phen and 3 is performed by time-dependent density functional methods. Fluorescence is predicted with a low quantum yield at 386 nm, and dual phosphorescence from n−π* and π−π* triplet states is predicted at 523 and 496 nm. Emission quenching was demonstrated for 3 and explained by nonradiative decay involving supramolecular stacking and low-lying metal-centered states. ■ INTRODUCTIONFor decades Cu(II) coordination compounds have been attractive targets for magneto-and biochemistry. 1,2 Engineering of metal−organic materials with specific properties using a molecular building blocks approach is possible only by understanding the interplay of different interactions involved in self-assembly processes. From a crystal engineering perspective, one of the advantages of using transition metal ions is that the shape of the main building block can be controlled by way of organic ligand-bound metal-containing modules in directions dictated by the coordination geometry of the metal center and by careful choice of the ligands. 3−8 Design strategies employing simultaneously coordination bonds, hydrogen bonds, and π−π stacking interactions in crystal engineering are mostly not well documented so far. 9 We are involved in engineering, structural studies, and evaluation of properties of low-dimensional clusters and coordination polymers that include the Cu(II)−phen building block and reveal the contribution of stacking interactions in the crystal packing. 10,11 The necessity of careful examination and disclosure of the robust recurring patterns in such lowdimensional solids is dictated by their wide exploitation as medicinal forms with obvious antitumor efficacy. It has been reported that, in particular, phen derivatives [Cu-(CH 3 COO) 2 (phen)] and [Cu(sal)(phen)] demonstrate approximately seven times higher activity than cisplatin against HepG2, A-498, and A-549 cancer cells. Among the factors that influence the cytotoxic activity, the...

Ten Zn­(II) and Cd­(II) metal–organic materials were synthesized and studied by the X-ray method. Among these 10 structures, two represent binuclear clusters, and two are one-dimensional (1D) coordination polymers, while five are laminar two-dimensional (2D) solids and one is the three-dimensional (3D) framework. The investigation has been aimed at rational design of coordination polymers decorated by oxime ligands to increase the accessible adsorption area in these newly synthesized solids. The ligands used include three aliphatic dicarboxylic acids, HOOC-(CH2) n -COOH [n = 1, 2, 4 corresponding to malonic (H2mal), succinic (H2suc), and adipic (H2adi) acids], and three neutral oxime ligands [pyridine-2-aldoxime (2-pyao), pyridine-4-aldoxime (4-pyao), and 1,2-cyclohexanedionedioxime (Niox)]. These novel hybrid solids with the compositions [Zn2(suc)2­(2-pyao)4]­·2H2O 1, [Cd2(suc)­(2-pyao)4(H2O)2]­[BF4]2 2, [Cd­(suc)­(2-pyao)2] n 3, [Zn­(mal)­(4-pyao)­(H2O)] n 4, [Cd­(mal)­(4-pyao)­(H2O)] n 5, [Zn­(suc)­(4-pyao)] n 6, [Zn­(adi)­(4-pyao)2] n 7, {[Cd­(adi)­(4-pyao)2]·dmf} n 8, [Zn­(adi)­(Niox)] n 9, and [Cd­(adi)­(Niox)] n 10 [dmf – N ,N′-dimethylformamide] demonstrate a variable class of coordination supramolecular architectures dictated by the distinctions in the metals’ and oxime ligands’ coordination capacities and preferences, and length and flexibility of the dicarboxylic linkers. The discrete aggregates 1 and 2 differ by the components’ ratio and conformation of the bridging succinate anion; compounds 3 and 7 are 1D arrays, and compounds 4, 5, 6, 8, and 9 represent 2D layers of different topologies. Compound 10 is a 3D grid afforded by the concerted contribution of the longest in this series adipate anion, and the bigger atomic radius Cd­(II) vs. Zn­(II). The adsorptive properties of 7 and 9 are reported. For the laminar solid 9, the quantum chemical simulations of the adsorption capacity are in line with the experimental results. All new materials reveal dual green-blue wavelength emission in the solid state.

The cellular environment is crowded with high concentrations of macromolecules that significantly reduce accessible volume for biomolecular interactions. Reductions in cellular volume can generate depletion forces that affect protein assembly and stability. The mechanical and structural properties of actin filaments play critical roles in various cellular functions, including structural support, cell movement, division, and intracellular transport. Although the effects of molecular crowding on actin polymerization have been shown, how crowded environments affect filament mechanics and structure is unknown. In this study, we investigate the effects of solution crowding on the modulations of actin filament bending stiffness and conformations both in vitro and in silico. Direct visualization of thermally fluctuating filaments in the presence of crowding agents is achieved by fluorescence microscopy imaging. Biophysical analysis indicates that molecular crowding enhances filament's effective bending stiffness and reduces average filament lengths. Utilizing the all-atom molecular dynamics simulations, we demonstrate that molecular crowding alters filament conformations and intersubunit contacts that are directly coupled to the mechanical properties of filaments. Taken together, our study suggests that the interplay between excluded volume effects and nonspecific interactions raised from molecular crowding may modulate actin filament mechanics and structure.

The synthesis and comprehensive linear spectroscopic and nonlinear optical properties of a new BODIPYbased fluorene-containing derivative 4,4-difluoro-8-(4-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}phenyl)-1,3,5,7-tetramethyl-2,6-di [(9,9-di{2-[2-(2-methoxyethoxy)ethoxy]ethyl}-9H-fluoren-2-yl)ethynyl]-4-bora-3a,4a-diaza-s-indacene (1) are reported. The steady-state absorption, emission, and excitation anisotropy spectra along with fluorescence lifetimes of 1 were analyzed in organic solvents of different polarity. The degenerate two-photon absorption (2PA) spectrum of 1 was obtained over a broad spectral range by the open aperture Zscan method using 1 kHz femtosecond excitation, and the 2PA cross section had a maximum value of ∼400 GM. The onephoton stimulated emission depletion spectrum of 1 was determined by a fluorescence quenching method with values of stimulated emission cross sections close to the corresponding ones of the ground state linear absorption. The nature of ultrafast relaxation processes in 1 was analyzed by a transient absorption femtosecond pump−probe technique, and the characteristic times of intramolecular relaxations between the excited electronic states (<150 fs) and solvation dynamics (4−6 ps) were determined. Efficient superluminescence emission of 1 was observed in solution under one-and two-photon femtosecond pumping. Detailed analysis of the singlet excitations in 1 was performed by a time-dependent density functional theory (TD-DFT) method. Three one-photon and two two-photon absorbing states were predicted in the wavelength range investigated. A reactive handle was included in the meso-position of the BODIPY chromophore to facilitate future bioconjugation or functionalization for bioimaging applications.

Interaction of zinc(II) and cadmium(II) sulfates with pyridine-4-aldoxime (4-pyao) and pyridine-4amidoxime (4-pyamo) ligands resulted in four 1D metal− organic materials (MOMs) with identical composition, [M(SO 4 )A 2 (H 2 O) 2 ] n , where M = Zn(II), A = 4-pyao for 1, M = Cd(II), A = 4-pyao for 2, M = Zn(II), A = 4-pyamo for 3, M = Cd(II), A = 4-pyamo for 4, and mononuclear [Zn(SO 4 )(4-pyamo) 2 (H 2 O) 3 ] 5. New coordination polymers represent the mixed-ligand supramolecular isomers different by the twisting of two pyridine-4-oxime ligands in the metal coordination environments, and crystallizing in the different space groups.Conformational preferences and nonlinear optical properties of the 4-pyao and 4-pyamo complexes were investigated using density functional theory. Spectral properties of 1−3 have been also evaluated. The solid-state emission of 1D polymers 1−3 appears to be ligand-based, as the positions of the emission maxima remain practically unchanged from free ligand to complexes. The enhancement of luminescence and twophoton absorption in polymers in comparison with the pure ligands is attributed to the chelation of the ligand to the metal center. The detailed mechanism of this enhancement upon complex formation is analyzed and can be used in future design of metal−organic nonlinear optical materials.