Optical limiting properties of zinc phthalocyanines in solution and solid PMMA composite films

The nonlinear absorption and optical limiting (OL) performance of tetra- and octasubstituted zinc phthalocyanine complexes were described in solution and in the solid state using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The polymeric films exhibit a much larger effective nonlinear absorption coefficient in comparison with solution. However, the parameters of the ratio of the excited to ground state absorption cross section and energy-dependent saturation in solution are much better compared to properties in the polymeric film. In terms of the ratio of the excited to ground state absorption cross section, the peripherally substituted complexes show better OL performance than the non-peripherally substituted derivative

Thickness-dependent nonlinear absorption behaviors in polycrystalline ZnSe thin films

Polycrystalline ZnSe thin films have been deposited with different thicknesses by using sputtering evaporation method. Their nonlinear absorption behaviors were investigated by open aperture Z-scan and pump-probe techniques. Linear absorption measurements show redshift in energy as the film thickness increases. This can be attributed to Urbach tail effect. All films exhibit nonlinear absorption for 65 ps pulse duration at lower input intensities while they exhibit saturable absorption at higher input intensities. The life time of localized defect states on grain boundary was found to be similar to 3 ns from ultrafast pump-probe spectroscopy. Nonlinear absorption coefficients and saturation intensity thresholds were extracted from the fitting of the experimental data for 65 ps pulse duration. They increase with increasing film thickness. This behavior can be attributed to the increasing localized defect states on grain boundaries as the film thickness increases

Optical limiting properties of zinc phthalocyanines in solution and solid PMMA composite films

The nonlinear absorption and optical limiting (OL) performance of tetra- and octasubstituted zinc phthalocyanine complexes were described in solution and in the solid state using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The polymeric films exhibit a much larger effective nonlinear absorption coefficient in comparison with solution. However, the parameters of the ratio of the excited to ground state absorption cross section and energy-dependent saturation in solution are much better compared to properties in the polymeric film. In terms of the ratio of the excited to ground state absorption cross section, the peripherally substituted complexes show better OL performance than the non-peripherally substituted derivative

Excited state dynamics of nanocrystalline VO2 with white light continuum time resolved spectroscopy

In an attempt to use ultrafast pump probe spectroscopy technique with white light continuum to reveal wavelength dependent dynamics of VO2, bandgap needs to be opened. Therefore, nanostructured amorphous and crystalline VO2 thin films were prepared with pulsed DC magnetron reactive sputtering. The mean diameters of grains were measured as 22 +/- 0.1 nm and 44 +/- 0.1 nm for amorphous and crystalline VO2 thin films, respectively. Temperature dependent resistance measurements show that nanocrystalline VO2 thin film exhibit metal insulator phase transition. The films exhibited dual band gaps (2.3 eV, AbstractIn an attempt to use ultrafast pump probe spectroscopy technique with white light continuum to reveal wavelength dependent dynamics of VO2, bandgap needs to be opened. Therefore, nanostructured amorphous and crystalline VO2&nbsp;thin films were prepared with pulsed DC magnetron reactive sputtering. The mean diameters of grains were measured as 22&plusmn;0.1&nbsp;nm and 44&plusmn;0.1&nbsp;nm for amorphous and crystalline VO2&nbsp;thin films, respectively. Temperature dependent resistance measurements show that nanocrystalline VO2&nbsp;thin film exhibit metal insulator phase transition. The films exhibited dual band gaps (2.3&nbsp;eV, &lt;0.6&nbsp;eV for amorphous films and 1.3&nbsp;eV, 1.8&nbsp;eV for crystalline film). Increased band gaps made it possible to perform time resolved transmission and reflection experiments with white light continuum at fluences above and below photo induced phase transition threshold. Although transmission chance due to photo induced phase transition of VO2&nbsp;in the literature usually takes places at infrared region of the spectrum, transmission chance was observed in visible as low as 630&nbsp;nm in broadband probe spectra. It was observed that measured time scales depend on not only pump fluence but also probe wavelength. Experiments gave the evidence of the long-lived lower energy non-equilibrium state related to the photo induced phase.</p

Fabrication of Supramolecular n/p-Nanowires <i>via</i> Coassembly of Oppositely Charged Peptide-Chromophore Systems in Aqueous Media

Fabrication of supramolecular electroactive materials at the nanoscale with well-defined size, shape, composition, and organization in aqueous medium is a current challenge. Herein we report construction of supramolecular charge-transfer complex one-dimensional (1D) nanowires consisting of highly ordered mixed-stack π-electron donor–acceptor (D–A) domains. We synthesized n-type and p-type β-sheet forming short peptide-chromophore conjugates, which assemble separately into well-ordered nanofibers in aqueous media. These complementary p-type and n-type nanofibers coassemble <i>via</i> hydrogen bonding, charge-transfer complex, and electrostatic interactions to generate highly uniform supramolecular n/p-coassembled 1D nanowires. This molecular design ensures highly ordered arrangement of D–A stacks within n/p-coassembled supramolecular nanowires. The supramolecular n/p-coassembled nanowires were found to be formed by A–D–A unit cells having an association constant (<i>K</i>_A) of 5.18 × 10⁵ M^–1. In addition, electrical measurements revealed that supramolecular n/p-coassembled nanowires are approximately 2400 and 10 times more conductive than individual n-type and p-type nanofibers, respectively. This facile strategy allows fabrication of well-defined supramolecular electroactive nanomaterials in aqueous media, which can find a variety of applications in optoelectronics, photovoltaics, organic chromophore arrays, and bioelectronics

Building an iron chromophore incorporating prussian blue analogue for photoelectrochemical water oxidation

The replacement of traditional ruthenium-based photosensitizers with low-cost and abundant iron analogs is a key step for the advancement of scalable and sustainable dye-sensitized water splitting cells. In this proof-of-concept study, a pyridinium ligand coordinated pentacyanoferrate(II) chromophore is used to construct a cyanide-based CoFe extended bulk framework, in which the iron photosensitizer units are connected to cobalt water oxidation catalytic sites through cyanide linkers. The iron-sensitized photoanode exhibits exceptional stability for at least 5 h at pH 7 and features its photosensitizing ability with an incident photon-to-current conversion capacity up to 500 nm with nanosecond scale excited state lifetime. Ultrafast transient absorption and computational studies reveal that iron and cobalt sites mutually support each other for charge separation via short bridging cyanide groups and for injection to the semiconductor in our proof-of-concept photoelectrochemical device. The reorganization of the excited states due to the mixing of electronic states of metal-based orbitals subsequently tailor the electron transfer cascade during the photoelectrochemical process. This breakthrough in chromophore-catalyst assemblies will spark interest in dye-sensitization with robust bulk systems for photoconversion applications

Building an iron chromophore incorporating prussian blue analogue for photoelectrochemical water oxidation

Invited for the cover of this issue is the Ferdi Karadas and Ekmel Ozbay groups at Bilkent University and co-workers. The image presents an utopic city in Iron Age, which is powered by an iron photosensitizer that bridges semiconductor buildings (TiO2 nanowires) and the catalyst (cobalt site). Read the full text of the article at 10.1002/chem.202100654

Efficient Intersystem Crossing in Heavy-Atom-Free Perylenebisimide Derivatives

Efficient intersystem crossing (ISC) in heavy-atom-free organic chromophores remains rare because of the lack of strong spin–orbit coupling effects in such compounds. Finding organic chromophores with ISC ability is important for applications in several areas, e.g., photocatalysis and photodynamic therapy. Herein, we report new perylenebisimide (PBI) chromophores with tetraphenylethynyl substituents at the 2,5,8,11-positions of the PBI core (<i>ortho</i>-positions, not the usually reported <i>bay</i>-positions of PBI), which show efficient ISC without the presence of any heavy atoms. Steady-state and picosecond–nanosecond transient absorption spectroscopies as well as time-dependent density functional theory computations were used to reveal the photophysical properties. For one of the PBI derivatives, excitation wavelength-dependent ISC was observed. The efficient ISC was attributed to the S₁/S₂ → T_<i>n</i> (<i>n</i> > 1) processes. Photochemical reduction of the PBI derivatives in the presence of a sacrificial electron donor (triethanolamine) produced a stable PBI radical anion