Ayhan Elmali

BODIPY triads triplet photosensitizers enhanced with intramolecular resonance energy transfer (RET): broadband visible light absorption and application in photooxidation

Resonance energy transfer (RET) was used to enhance the light absorption in triad triplet photosensitizers to access strong and broadband absorption in visible region (from 450–750 nm). This strategy was demonstrated by preparation of (BODIPY)2-diiodo-aza-BODIPY triad (B-2) and (carbazole-styryl BODIPY)2-diiodo-aza-BODIPY triad (B-3), in which the energy donor (BODIPY or styryl-BODIPY) and the energy acceptor (aza-BODIPY, also as the spin converter) parts were connected by click chemistry. Both the energy donors and the energy acceptors show strong absorption in the visible spectral region, but at different wavelengths, therefore the triads show broadband absorption in visible spectra region, e.g. the two major absorption bands of B-3 are located at 593 nm and 683 nm, with e up to 220000 M−1 cm−1 and 81000 M−1 cm−1, respectively. For comparison, a reference compound with only diiodo-aza-BODIPY as the light-harvesting unit was prepared (B-1), which shows only one major absorption band in visible spectral region. Fluorescence studies indicated intramolecular energy transfer for these BODIPY hybrids, a conclusion which is supported by the femtosecond time-resolved transient absorption spectroscopy. Nanosecond transient absorption spectra show that triplet excited states of the dyad and the triad are localized on the iodo-aza-BODIPY part. The compounds were used as triplet photosensitizers for singlet oxygen (1O2) mediated photooxidation of 1,5-dihydroxylnaphthalene and the photosensitizing ability of the new triplet photosensitizers are more efficient than the mono-chromophore based triplet photosensitizers. The molecular design rationale of these RET-enhanced multi-chromophore triplet photosensitizer is useful for development of efficient triplet photosensitizers and for their applications in photocatalysis, photodynamic therapy, photovoltaics and upconversion.

Good optical limiting performance of indium and gallium phthalocyanines in a solution and co-polymer host

The optical limiting characteristics of tetra- and octasubstituted gallium and indium phthalocyanine complexes have been studied by means of the open-aperture Z-scan technique with nanosecond pulses at 532 nm. The nonlinear response demonstrated that all investigated compounds exhibited strong reverse saturable absorption for both solution and solid-state-based experiments. The results showed that the ratio of the excited to ground state absorption cross section κ and effective nonlinear absorption coefficient βeff are largely dependent on the linear absorption coefficient. All compounds in chloroform exhibited almost the same optical limiting performance at the same linear absorption coefficient. Pc/PMMA composite films display a much larger effective nonlinear absorption coefficient, lower ratio of the excited to ground state absorption cross section and lower saturation fluence for optical limiting when compared to the same Pc molecules in solution. All gallium and indium complexes of phthalocyanines are good candidates for optical limiting applications.

Conformational study and structure of N-(2,5-methylphenyl)salicylaldimine

Abstract N-(2,5-methylphenyl)salicylaldimine (C15H15NO) has been investigated by X-ray analysis and AM1 semi-empirical quantum mechanical method. The crystal is in the orthorhombic space group P212121 with a = 6.839(1), b = 7.720(4), c = 23.183(3) A , V = 1224.1(2) A 3 , Z = 4, Dc = 1.222 g cm−3 and μ(Mo Kα) = 0.076 mm−1. The title structure was solved by direct methods and refined to R = 0.0364 for 1489 reflections [I > 2σ(I)] by full-matrix anisotropic least-squares methods. The title compound is photochromic and the molecule is not planar. There is a strong intramolecular hydrogen bond of distance 2.604(2) A between the hydroxyl oxygen atom and imine nitrogen atom, the hydrogen atom essentially being bonded to the oxygen atom. Minimum energy conformations from AM1 were calculated as a function of three torsion angles, θ1 (C8N1C7C6), θ2 (C9C8N1C7) and θ3 (N1C7C6C5), varied every 10°. The optimized geometry of the crystal structure corresponding to non-planar conformation is the most stable conformation in all calculations. The results strongly indicate that the minimum energy conformation is primarily determined by non-bonded hydrogen-hydrogen repulsions.

Structure and conformation of N-(2-methyl-5-chlorophenyl)salicylaldimine

Abstract N-(2-methyl-5-chlorophenyl)salicylaldimine (C14H12ClNO) has been studied by X-ray analysis and AM1 molecular orbital methods. It crystallises in the orthorhombic space group P212121 with a = 7.474(1) A , b = 12.155(1) A , c = 13.378(1) A , V = 1215.3(2) A 3 , Z = 4, Dc = 1.343 g cm−3 and μ(Mo Kα) = 0.296 mm−1. The structure was solved by direct methods and refined to R = 0.0374 for 1689 reflections [I > 2σ(I)]. The title compound is photochromic and the molecule is not planar. There is a strong intramolecular hydrogen bond of distance 2.604(3) A between the hydroxyl oxygen atom and imine nitrogen atom, the hydrogen atom essentially being bonded to the oxygen atom. Minimum energy conformations from AM1 were calculated as a function of the three torsion angles θ1(C8N1C7C6), θ2(C9C8N1C7) and θ3(N1C7C6C5), varied every 10°. The optimised geometry of the crystal structure corresponding to a non-planar conformation is the most stable conformation in all calculations.

Synthesis, characterization and nonlinear absorption of novel octakis-POSS substituted metallophthalocyanines and strong optical limiting property of CuPc

In this study, the preparation of some novel metallophthalocyanine (MPcs) complexes substituted with octakis(mercaptopropylisobutyl-POSS) functional group was achieved. By the reaction of [1-(3-mercapto)propyl-3,5,7,9,11,13,15-isobutylpentacyclo[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxane 1 with 4,5-dichloro-1,2-dicyanobenzene 2 in THF as the solvent in the presence of K2CO3 as the base, the phthalonitrile derivative 3 was synthesized. Compound 3 reacted with CoCl2 x 6H2O in ethylene glycol to furnish a novel cobalt(II) phthalocyanine . The tetramerization of 3 with urea and CuCl in the absence of solvent gave the novel Cu(II) phthalocyanine 4; while with Zn(OAc)2 x 2H2O in dry DMF gave the novel zinc(ii) phthalocyanine 6. The structures of the target compounds were confirmed by elemental analysis, UV/VIS, IR, MALDI-TOF MS and 1H NMR spectra. Nonlinear absorptions of MPcs in chloroform solution were investigated by using Z-scan measurement technique with 4 ns pulses at 532 nm wavelength. While CuPc 5 showed very high nonlinear absorption, MPcs 4 and 6 did not show considerable nonlinear absorption. Investigations of optical limiting properties of 5 revealed that this material is a very good candidate for optical limiting applications.

DiiodoBodipy-Perylenebisimide Dyad/Triad: Preparation and Study of the Intramolecular and Intermolecular Electron/Energy Transfer

2,6-diiodoBodipy-perylenebisimide (PBI) dyad and triad were prepared, with the iodoBodipy moiety as the singlet/triplet energy donor and the PBI moiety as the singlet/triplet energy acceptor. IodoBodipy undergoes intersystem crossing (ISC), but PBI is devoid of ISC, and a competition of intramolecular resonance energy transfer (RET) with ISC of the diiodoBodipy moiety is established. The photophysical properties of the compounds were studied with steady-state and femtosecond/nanosecond transient absorption and emission spectroscopy. RET and photoinduced electron transfer (PET) were confirmed. The production of the triplet state is high for the iodinated dyad and the triad (singlet oxygen quantum yield ΦΔ = 80%). The Gibbs free energy changes of the electron transfer (ΔGCS) and the energy level of the charge transfer state (CTS) were analyzed. With nanosecond transient absorption spectroscopy, we confirmed that the triplet state is localized on the PBI moiety in the iodinated dyad and the triad. An exceptionally long lived triplet excited state was observed (τT = 150 μs) for PBI. With the uniodinated reference dyad and triad, we demonstrated that the triplet state localized on the PBI moiety in the iodinated dyad and triad is not produced by charge recombination. These information are useful for the design and study of the fundamental photochemistry of multichromophore organic triplet photosensitizers.

Nonlinear and saturable absorption characteristics of amorphous InSe thin films

We prepared very thin amorphous InSe films and investigated the thickness dependence of the nonlinear absorption by pump-probe and open aperture Z-scan techniques. While thinner films (20 and 52 nm) exhibit saturable absorption, thicker films (70 and 104 nm) exhibit nonlinear absorption for 4 ns, 65 ps, and 44 fs pulse durations. This behavior is attributed to increasing localized defect states in the energy band gap as the film thickness increases. We developed a theoretical model incorporating one photon, two photon, and free carrier absorptions and their saturations to derive the transmission in the open aperture Z-scan experiment. The theory of open aperture Gaussian beam Z-scan based on the Adomian decomposition method was used to fit the experimental curves. Nonlinear absorption coefficients along with saturation intensity thresholds were extracted from fitting the experimental results for all pulse durations. The lowest saturation threshold was found about 3×10−3 GW/cm2 for 20 nm film thickness wit...

Electrochemically tunable ultrafast optical response of graphene oxide

dation. Here, we study the effect of the oxidation level on nonlinear optical properties of GO. We demonstrate that both electrochemically induced reversible reduction and optically induced photoreduction in GO result in changes in the nonlinear optical properties of GO thin films. We present the carrier dynamics and nonlinear optical properties of such films, studied by ultrafast wavelength-dependent pumpprobe spectroscopy. We show that ultrafast response of GO can be tuned by both reduction procedure. The preparation, characterization, linear optical, and electrochromism properties of GO were very recently reported. 10 We study the electrical reduction in GO in air, using multilayer GO thin films deposited on metalized glass substrates. The two terminal devices consist of thin 10‐50 nm Pd/Au planar contacts, separated by 0.3‐0.6 mm, with a thin multilayer GO film covering both contacts and in between Fig. 1a. The degree of chemical reduction and linear absorption spectrum can be tuned by applying a

Magnetic properties of PrMn2-xFexGe2 compounds

Abstract The structure and magnetic properties of the PrMn 2− x Fe x Ge 2 (0.0≤ x ≤1.0) compounds have been investigated by means of X-ray diffraction and magnetic measurements. All compounds crystallize in the ThCr 2 Si 2 -type structure with the space group I 4/ mmm . The lattice constants and the unit cell volume obey Vegard’s law. The samples with x ≤0.4 are ferromagnetic and show an additional increase in the magnetization due to magnetic ordering of the Pr sublattice at low temperatures. Reentrant ferromagnetism has been observed for x =0.6. The compounds with x =0.8 and x =1.0 are antiferromagnetic. The results lead to the construction of the partial x −T magnetic phase diagram.

Resonance energy transfer-enhanced rhodamine–styryl Bodipy dyad triplet photosensitizers

Organic triplet photosensitizers (R-1 and R-2) enhanced with the resonance energy transfer (RET) effect were prepared. Rhodamine was used as an intramolecular energy donor, and iodo-styryl-Bodipy was used as intramolecular energy acceptor/spin converter. Both the energy donor and energy acceptor in R-1 and R-2 give strong absorption in the visible region but at different wavelengths (e.g. for R-1, e = 120 000 M−1 cm−1 at 557 nm for the energy donor and e = 73 300 M−1 cm−1 at 639 nm for the energy acceptor). As a result, the photosensitizers show broadband absorption in the visible spectral region. In comparison, conventional triplet photosensitizers contain only one visible light-harvesting chromophore; thus, there is usually only one major absorption band in the visible spectral region. Using steady state and time-resolved spectroscopy, we demonstrated that photoexcitation in the energy donor was followed by intramolecular singlet energy transfer, and then via intersystem crossing (ISC) of the energy acceptor (spin converter), triplet excited states localized on the iodo-styryl-Bodipy were produced, which was confirmed by nanosecond time-resolved transient difference absorption spectroscopy. The organic dyad triplet photosensitizers were used for photoredox catalytic organic reactions to prepare pyrrolo[2,1-a]isoquinoline, and we found that the photocatalytic capability was improved with the RET effect. The dyads were also used as fluorescent stains for LLC cancer cells. Photodynamic effect was observed with the same cells, which were killed on photoirradiation with 635 nm red-emitting LED after incubation with the triplet photosensitizers. Therefore, these photosensitizers can be potentially developed as dual functional theranostic reagents. Using the molecular structural protocol reported herein, organic triplet photosensitizers with strong broadband absorption in the visible spectral region and predictable ISC can be easily designed. These results are useful for the study of organic triplet photosensitizers in the area of organic photochemistry/photophysics, photoredox catalytic organic reactions and photodynamic therapy (PDT).