We exploit the strong spin-orbit coupling in iridium to modify the linear absorption spectrum of a novel iridium(III) complex so as to broaden the spectral region over which it exhibits reverse saturable absorption. We discuss the design of the new chromophore, present its ground-state absorption spectrum, and report values of its singlet excited-state lifetime and singlet and triplet excited-state absorption cross sections, determined from femtosecond transient difference absorption measurements and nanosecond and picosecond open-aperture Z scans.
In top-hat Z scans that employ tunable sources such as optical parametric generators without line-narrowing gratings, the size of the aperture used to clip the beam may exceed the coherence length, and the variation with z of the transverse profile of the resulting partially coherent beam may differ significantly from that of a perfect top-hat beam. After a careful validation of our experimental set-up, we perform picosecond open-aperture Z scans with a top-hat beam at selected wavelengths in the visible and nanosecond open-aperture Z scans with a spatially Gaussian beam at 532-nm wavelength on a toluene solution of a particular platinum(II) 2,2′-bipyridyl complex bearing naphthalimidylethynyl-substituted fluorenylacetylide ligands. We report values of the singlet and triplet excited-state absorption cross sections of the complex.
We report the results of measurements performed on a particular platinum(II)
4,4'-bis[3-ethyl-1-(2-ethylhexyl)heptyl]-2,2'-bipyridyl complex bearing 2-(benzothiazol-2'-yl)-7-ethynyl-9,9-dihexadecyl-fluorenyl units. A similar complex,
identical except for the presence of ethyl groups at the 9-position of the fluorenes and tert-butyl groups at the 4- and
4'- positions of the bipyridine, was recently reported to possess a very high ratio of triplet excited-state absorption to
ground-state absorption, a quantity that has long been used as a figure of merit for reverse saturable absorbers; in
addition, femtosecond transient difference absorption experiments and picosecond open-aperture Z-scans have shown it
to display broad nonlinear absorption throughout the visible spectrum. In this work, we measured the triplet excitedstate
absorption cross section at several representative wavelengths between 450 nanometers and 660 nanometers in an
open-aperture top-hat Z-scan experiment employing a
nanosecond-pulsed tunable optical parametric oscillator (OPO).
The open-aperture Z-scan is a highly sensitive single-beam experiment used to measure nonlinear absorption. Since the
spatial profile of the OPO beam resembled a cross-pattern, we closed an adjustable iris on the beam to create a top-hat
profile. A dynamic five-level model was used to fit the Z-scan data.
After the premier commercialization of OLED in 1997, OLED has been considered as the candidate for the next
generation of flat panel display. In comparison to liquid crystal display (LCD) and plasma display panel (PDP), OLED
exhibits promising merits for display, e.g., flexible, printable, micro-buildable and multiple designable. Although many
efforts have been made on electroluminescent (EL) materials and devices, obtaining highly efficient and pure blue light
is still a great challenge. In order to improve the emission efficiency and purity of the blue emission, a new bipolar blue
light emitter, 2,7-di(2,2′:6′,2"-terpyridine)- 2,7-diethynyl-9,9-dioctyl-9H-fluorene (TPEF), was designed and
synthesized. A blue OLED was obtained with the configuration of ITO/PEDOT/PVK:CBP:TPEF/LiF/Al. The device
exhibits a turn-on voltage of 9 V and a maximum brightness of 12 cd/m2 at 15 V. The device gives a deep blue emission
located at 420 nm with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.10). We also use
TPEF as electron transporting material in the device of ITO/PPV/TPEF/LiF/Al, the turn-on voltage is 3 V. It is proved
the current in the device was enhanced indeed by using the new material.
Organic materials with large two-photon absorption are desired for numerous photonics applications, such as optical limiting,upconversion lasing, three-dimensional data storage,and photodynamic therapy. Stilbazolium derivatives are interesting two-photon absorbers for these applications. In this work,the nonlinear transmissivities of trans -4-[4-(dimethylamino)styryl ]-1-methylpyridinium iodide (DASPI),trans -4-(4-aminostyryl)-1-methylpyridinium iodide (ASPI),trans -4-[2-(1-methylpyrryl)vinyl ]-1-methylpyridinium iodide (MPVPI),trans -4-(2-pyrrylvinyl)-1-methylpyridinium iodide (PVPI),and trans -4-styryl-1-methylpyridinium iodide (SPI)at 800,850,900,950 and 1000 nm have been studied respectively using 21 ps laser pulses. The two-photon induced fluorescence of these compounds at 872,900,and 940 nm has also been investigated.All of these compounds exhibit two-photon absorption and two-photon induced up-converted fluorescence in the near-IR wavelengths,and the two-photon absorption cross section and
two-photon induced fluorescence intensity vary with the wavelength and with the chemical structure changes. These preliminary results suggest that it is possible to increase the two-photon absorption cross-sections by proper structure modifications
Organic materials with large excited state and/or two-photon absorption are desired for numerous device applications, such as optical limiting, two-photon upconversion lasing, three-dimensional data storage, and two-photon photodynamic therapy. Dialkylamino styryl thiazolium/benzoxazolium compounds are interesting excited state and two-photon absorbers for these applications. In this work, the nonlinear transmissivity of trans-2-[p-(N-methyl-N-(hydroxyethyl)amino)styryl]-N-methylthiazolium iodide (MHAST), trans-2-[p-(N-ethyl-N-(hydroxyethyl)amino)styryl]-N-methylthiazolium hexafluorophosphate (EHAST), trans-2-[p-(N-methyl-N-(hydroxyethyl)amino)styryl]-N-methylbenzoxazolium iodide (MHASBO) at 532 nm has been studied using 6 ns laser pulses. The two-photon induced fluorescence of these compounds at 940 nm has also been investigated. At 532 nm, both MHAST and EHAST exhibit reverse saturable absorption, however, MHASB exhibit saturable absorption. At 940 nm, all of these compounds exhibit two-photon induced up-conversion fluorescence, and the fluorescence intensity varies when the chemical structure changes. These preliminary results suggest that the nonlinear absorption (excited state absorption or two-photon absorption) characteristics of these compounds vary at different wavelengths and vary when their chemical structure changes.
Stilbazolium derivatives are very attractive nonlinear optical (NLO) materials for photonics and biophotonics applications due to their low linear absorption at low incident intensities in most of the visible spectral range and potentially very strong nonlinear absorption at high intensities. In this work, we investigated the nonlinear absorption of five stilbazolium derivatives, trans-4-[2-(pyrryl)vinyl]-1-methylpyridinium iodide (PVPI), trans-4-[2-(1-ferrocenyl)vinyl]-1-methylpyridinium iodide (FcVPI), trans-4-[2-(1-ferrocenyl)styryl]-1-methylpyridinium iodide (FcSPI), trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DASPI) and trans-4-(4-aminostyryl)-1-methylpyridinium iodide (ASPI) using 6 ns and 40 ps laser pulses at 532 nm. These compounds exhibit different nonlinear absorption behavior for nanosecond and picosecond laser pulses. In the nanosecond time regime, they all show reverse saturable absorption, with PVPI exhibiting the best result. With 90% linear transmission in a 2-mm cell, the transmittance of a chloroform solution of PVPI drops to 5% when the incident fluence is increased to 7 J/cm2. The nonlinear absorption behavior of these compounds is influenced dramatically by the nature of the electron donating group, with reverse saturable absorption decreasing in the order of PVPI>FcVPI>FcSPI>ASPI>DASPI. In contrast, for picosecond laser pulses, only PVPI exhibit slight reverse saturable absorption, while DASPI, FcVPI and FcSPI show saturable absorption, and ASPI shows no nonlinear absorption. The different nonlinear absorption for ns and ps laser pulses may be due to the relative contributions from triplet excited state absorption and singlet excited state absorption.
Stilbazolium-like dyes, which contain different heterocyclic groups as electron donors and an N-methylpyridinium iodide group as an electron acceptor, are very interesting optical limiting materials. These materials exhibit low linear absorption, but potentially very strong nonlinear absorption at high intensities. In this paper, the results from investigations of the third-order susceptibilities and nonlinear refractive indices of a stilbazolium-like dye, trans-4-[2-(pyrryl)vinyl]-1-methylpyridinium iodide (PVPI), in different solvents using degenerate four wave mixing (DFWM) and Z-scan techniques with 6.8 ns laser pulses at 532 nm are reported. The molecular second-order hyperpolarizability of PVPI increases from 1.6x10-31 esu in methanol to 3.4x10-29 esu in chloroform, a factor of 212. The third-order nonlinearity of this compound is dominated by nonlinear absorption, which leads to strong optical limiting of nanosecond laser pulses. The strength of the optical limiting is dramatically influenced by the solvent used, with limiting decreasing in the order chloroform>dichloromethane, 1,2- dichloroethane>methanol, acetonitrile. While both nonlinear absorption and nonlinear scattering contribute to the optical limiting, nonlinear absorption is the dominant mechanism.
The passive optical limiters are of significant for protecting sensors and human eyes from high intensity laser. The selection of materials is still one of the key for optical power limiters. The nonlinear optical properties of pentaazadentate metal complexes (PMC) were measured, the third-order optical nonlinear polarizabilities of 1.19~3.38x10-13esu were obtained, from which the molecular second order hyperpolarizabilities of 8.0x10-32~2.83x10-31esu were calculated. The optical limiting performances for PMC have been studied at 532nm for 8ns and 35ps pulses by using nonlinear absorption technique, in which the reverse saturable absorptions in the T1 and S1 states were responsible for the optical limitings. Experimental results demonstrated that the peripheral substituents and center metal ions influenced the third-order optical nonlinearities and the optical limiting performances of PMC.
The third-order nonlinear optical properties of a methyl substituted Texaphyrin, [(CH3-TXP)Cd]Cl, were studied by degenerate four wave mixing and Z-scan techniques using 40 ps laser pulses at 532 nm. The molecular second- order hyperpolarizability ((gamma) ), the excited-state absorption cross section ((sigma) ex), the nonlinear refractive cross section ((sigma) t), and the optical limiting performances at both nanosecond and picosecond time scales have been determined. We have also studied the third- order nonlinearity of SiNc, one of the most promising optical limiting materials in literature, for comparison. The (gamma) value for [(CH3-TXP)Cd]Cl is 6.9 X 10-31 esu, which is 4 times as larger as that of SiNc. The nonlinearity of [(CH3-TXP)Cd]Cl is predominantly electronic in origin with picosecond laser pulses. The excited-state absorption cross section ((sigma) ex) and the nonlinear refractive cross section ((sigma) t) obtained from the theoretical simulation and calculation of Z-scan results are 7.0 X 10-17 cm2 and 1.7 X 10-17 cm2, respectively. The complex shows strong optical limiting performance via reverse saturable absorption for 5 ns laser pulses. The nonlinear absorption of this molecule for 40 ps laser pulses exhibits a transition from reverse saturable absorption to saturable absorption when the fluence is higher than 0.3 J/cm2. These data suggest that this complex and related complexes are a promising class of nonlinear optical materials.
The passive optical limiters are of significant for protecting sensors and human eyes from high intensity laser. The selection of materials is still the key point for optical power limiters. The optical limiting performances for five new pentaazadentate metal complexes with transmission of 0.45 - 0.70 in a 1 cm cell in tetrahydrofuran have been measured at 532 nm with 35 ps pulses, in which the reverse saturable absorption from the singletyieldssinglet excited state is responsible for the optical limiting. The optical limiting thresholds of pentaazadentate and benzopentaazadentate cadmium complexes at T/To equals 0.5 are 44 mJ/cm2 and 146 mJ/cm2 respectively, the lowest nonlinear transmittance for pentaazadentate complex I is 7.7%, while the incident maximum fluence reaches to 881 mJ/cm2. The bounds of figure of merit-like are estimated at 1.7 - 8.7. The limiting thresholds are strongly influenced by the nature of the substituents on the benzene ring. Electron withdrawing groups of the complexes can enhance the limiting capability, while the effect of heavy atom acts opposite roles. The optical limiting abilities are compared with C60, tetra- phenyl-tetrabenzoporophyrin-zinc and octanoxyl- phthalocyanine free base at same conditions. The sequence of the limiting capability is pentaazadentate cadmium complex >C60 > tetra-phenyl-tetrabenzoporphyrin-zinc > octanoxyl-phthalocyanine free base.
Pentaazadentate metal complexes are a macrocyclic ligand containing 22 (pi) -electrons, which coordinate with numerous metal ions to form near coplanar configurations with excellent thermal and light stabilities. A more extended optical window between Soret (420 nm) and Q (760 nm) band in visible region provides a condition for requiring high transmittances at low incident light intensity and they are of also large third- order nonlinear optical susceptibilities comparing with porphyrin's and phthalocyanine's metal complexes. The third- order optical susceptibilities (chi) (3)1111 are determined at 647 nm in methanol by pump-probed procedure and the molecular second hyperpolarizabilities (gamma) 1111 which are of approximately 10-31 esu are also obtained. Optical limiting based on reverse saturable absorption are observed for ns pulses laser. The optical limiting behaviors may be alternated by introduce different substituents onto the benzene ring or/and different metal ion into the center of macrocylic ligands The limiting threshold at T/T0 equals 0.5 is 131 mJ/cm2 for complex [(PL- NO2)Cd]Cl, the corresponding clamped energy is 34 mJ/cm2. The optical limiting performance may be influenced by solution concentrations.
Detailed degenerate four wave mixing (DFWM) studies of one molybdenum complex, cis-Mo(CO)4(PPh3)2 in dichloromethane (CH2Cl2) and tetrahydrofuran (THF) are reported in this paper. Upon exposure to air/oxygen, the (chi) (3) values of CH2Cl2 and THF solutions of this complex increase dramatically with time. However, when excess free ligand is added to CH2Cl2 solution of the complex, the increase in (chi) (3) value is stopped. Hence, it is possible to obtain a CH2Cl2 solution with high (chi) (3) value by first oxidizing the solution and then adding excess ligand to stabilize the solution. For THF solution, probably due to the different mechanism causing the increase of (chi) (3) values, the increase in (chi) (3) values doesn't stop even though excess free ligand is added. Further, the increase in the (chi) (3) values of both the CH2Cl2 and THF solutions parallels the increase in the linear absorption but it is unclear whether the increased linear absorption plays any role in the increase in the (chi) (3) value of the solution. This study also shows how degenerate four wave mixing can be used as a very sensitive technique to detect the chemical change in a solution when the third order optical nonlinearities of the reactant and product are very different.
The optical limiting performances of nine asymmetric pentaazadentate porphyrin-like metal complexes {[(R- APPC)M]Cln} have been measured at 532 nm with nanosecond pulses. In a fl38 geometry, with sample transmission of 0.51 approximately 0.80 in a 2 mm cell, the limiting thresholds for these complexes were 1.4 approximately 150.0 mJ/cm2. The throughputs of these complexes were limited to 0.31 approximately 1.42 J/cm2 for incident fluences as high as 3.5 J/cm2. The limiting throughput was strongly influenced by the nature of the ligand and metal ions. Lower bounds for the ratio of triplet excited-state to ground state absorption cross sections have been estimated at 2.3 approximately 5.7. The lower limiting thresholds, lower limiting throughputs, as well as the ease of modification of the ligands and variation of the metal ions, make these complexes promising candidates for optical power limiters.
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