Showing papers by "Wright-Patterson Air Force Base published in 2000"
TL;DR: In this article, the use of procedures based on higher-order finite-difference formulas is extended to solve complex fluid-dynamic problems on highly curvilinear discretizations and with multidomain approaches.
Abstract: The use of procedures based on higher-order finite-difference formulas is extended to solve complex fluid-dynamic problems on highly curvilinear discretizations and with multidomain approaches. The accuracy limitations of previous near-boundary compact filter treatments are overcome by derivation of a superior higher-order approach. For solving the Navier-Stokes equations, this boundary component is coupled to interior difference and filter schemes with emphasis on Pade-type operators. The high-order difference and filter formulas are also combined with finite-sized overlaps to yield stable and accurate interface treatments for use with domain-decomposition strategies. Numerous steady and unsteady, viscous and inviscid flow computations on curvilinear meshes with explicit and implicit time-integration methods demonstrate the versatility of the new boundary schemes
491 citations
TL;DR: In this paper, the effects of friction-stir welded aluminum alloy 7050 in a T7451 temper to investigate the effects on the microstructure and mechanical properties were investigated.
Abstract: Aluminum alloy 7050 was friction-stir welded (FSW) in a T7451 temper to investigate the effects on the microstructure and mechanical properties. Results are discussed for the as-welded condition (as-FSW) and for a postweld heat-treated condition consisting of 121 °C for 24 hours (as-FSW + T6). Optical microscopy and transmission electron microscopy (TEM) examination of the weld-nugget region show that the FS welding process transforms the initial millimeter-sized pancake-shaped grains in the parent material to fine 1 to 5 µm dynamically recrystallized grains; also, the FS welding process redissolves the strengthening precipitates in the weld-nugget region. In the heat-affected zone (HAZ), the initial grain size is retained, while the size of the strengthening precipitates and of the precipitatefree zone (PFZ) is coarsened by a factor of 5. Tensile specimens tested transverse to the weld show that there is a 25 to 30 pct reduction in the strength level, a 60 pct reduction in the elongation in the as-FSW condition, and that the fracture path is in the HAZ. The postweld heat treatment of 121 °C for 24 hours did not result in an improvement either in the strength or the ductility of the welded material. Comparison of fatigue-crack growth rates (FCGRs) between the parent T7451 material and the as-FSW + T6 condition, at a stress ratio of R = 0.33, shows that the FCG resistance of the weldnugget region is decreased, while the FCG resistance of the HAZ is increased. Differences in FCGRs, however, are substantially reduced at a stress ratio of R = 0.70. Analysis of residual stresses, fatigue-crack closure, and fatigue fracture surfaces suggests that decrease in fatigue crack growth resistance in the weld-nugget region is due to an intergranular failure mechanism; in the HAZ region, residual stresses are more dominant than the microstructure improving the fatigue crack growth resistance.
460 citations
TL;DR: The chameleon's ability to change skin color depending on environment to increase its chances of surviving served as an inspiration in the development of self-adaptive supertough wear-resistant coatings as mentioned in this paper.
446 citations
31 May 2000-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a processing map has been developed on the basis of flow stress data as a function of temperature, strain rate and strain, which is used for obtaining processing windows and achieving microstructural control during hot working.
Abstract: The hot deformation behavior of Ti–6Al–4V with an equiaxed α–β preform microstructure is modeled in the temperature range 750–1100°C and strain rate range 0.0003–100 s−1, for obtaining processing windows and achieving microstructural control during hot working. For this purpose, a processing map has been developed on the basis of flow stress data as a function of temperature, strain rate and strain. The map exhibited two domains: (i) the domain in the α–β phase field is identified to represent fine-grained superplasticity and the peak efficiency of power dissipation occurred at about 825°C/0.0003 s−1. At this temperature, the hot ductility exhibited a sharp peak indicating that the superplasticity process is very sensitive to temperature. The α grain size increased exponentially with increase in temperature in this domain and the variation is similar to the increase in the β volume fraction in this alloy. At the temperature of peak ductility, the volume fraction of β is about 20%, suggesting that sliding of α–α interfaces is primarily responsible for superplasticity while the β phase present at the grain boundary triple junctions restricts grain growth. The apparent activation energy estimated in the α–β superplasticity domain is about 330 kJ mol−1, which is much higher than that for self diffusion in α-titanium. (ii) In the β phase field, the alloy exhibits dynamic recrystallization and the variation of grain size with temperature and strain rate could be correlated with the Zener–Hollomon parameter. The apparent activation energy in this domain is estimated to be 210 kJ mol−1, which is close to that for self diffusion in β. At temperatures around the transus, a ductility peak with unusually high ductility has been observed, which has been attributed to the occurrence of transient superplasticity of β in view of its fine grain size. The material exhibited flow instabilities at strain rates higher than about 1 s−1 and these are manifested as adiabatic shear bands in the α–β regime.
383 citations
TL;DR: Pendleton et al. as mentioned in this paper used the AAW flight research program to demonstrate, in full scale, key AAW parameters and to measure the aerodynamic, structural, and flight control characteristics associated with AAW.
Abstract: The Active Aeroelastic Wing (AAW) Flight Research Program's (Pendleton, E., Griffin, K., Kehoe, M., and Perry, B., A Flight Research Program for Active Aeroelastic Wing Technology, AIAA Paper 96-1574, April 1996 and Pendleton, E., Bessette, D., Field, P., Miller, G., and Griffin, K., The Active Aeroelastic Wing Flight Research Program, AIAA Paper 98-1972, April 1998) technical content is presented and analytical model development is summarized. Goals of the AAW flight research program are to demonstrate, in full scale, key AAW parameters and to measure the aerodynamic, structural, and flight control characteristics associated with AAW. Design guidance, derived from the results of this benchmark flight program, will be provided for implementation on future aircraft designs.
244 citations
233 citations
TL;DR: In this article, the effects of material constitutive behavior, tooling design, and friction conditions on metal flow, stress fields, and the tendency for tensile fracture during equal channel angular extrusion (ECAE) were established using a finite element modeling (FEM) technique.
207 citations
30 Nov 2000-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the grain size of IN 718 hot forged superalloy was predicted in the MDRx regime using compression tests on process annealed material, with a view to obtain a correlation between grain size and the process parameters.
Abstract: The hot deformation behavior of IN 718 superalloy has been characterized in the temperature range 900–1100°C and strain rate range 0.001–1.0 s−1 using compression tests on process annealed material, with a view to obtain a correlation between grain size and the process parameters. At a strain rate of 0.001 s−1, the material exhibits dynamic recrystallization (DRx) at 975°C and superplasticity at 1100°C, while metadynamic recrystallization (MDRx) occurs in the temperature range 950–1100°C and strain rate range 0.01–1.0 s−1. Unlike in the DRx domain, the grain size (d) variation in the MDRx regime could not be correlated with the standard Zener–Hollomon (Z) parameter due to strong thermal effects during cooling after hot deformation. However, it follows an equation of the type d=cexp(−Q/RT), where c, p and R are constants, Q the activation energy for MDRx and T the temperature. The value of p is very low (0.028) and the apparent activation energy is about 275 kJ mole−1, which is very close to that for self-diffusion in pure nickel. The data obtained from several investigators are in agreement with this equation. Such an equation combines the mild dynamic effect in MDRx with a stronger post-deformation cooling effect and may be used for predicting the grain size of IN 718 hot forged in the MDRx regime.
207 citations
29 Feb 2000-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The hot deformation behavior of ELI grade Ti-6Al-4V alloy with Widmanstatten preform microstructure over wide temperature (750-1100oC) and strain rate ranges (0.001-100 s−1) has been studied with the help of processing maps as discussed by the authors.
Abstract: The hot deformation behavior of extra-low interstitial (ELI) grade Ti–6Al–4V alloy with Widmanstatten preform microstructure over wide temperature (750–1100oC) and strain rate ranges (0.001–100 s−1) has been studied with the help of processing maps. In the lower temperature and strain rate regime (850–950°C and 0.001–0.1 s−1), globularization of the lamellar structure occurs while at higher temperatures (980–1100oC) the β phase exhibits large-grained superplasticity. The tensile ductility reaches peak values under conditions corresponding to these two processes. A dip in ductility occurs at the β transus and is attributed to a possible nucleation of voids within prior β grains. At lower temperatures and strain rates below about 0.1 s−1, cracking at the prior β grain boundaries occurs under mixed mode conditions. At strain rates higher than 1 s−1 and temperatures lower than about 950oC, the material exhibits a wide regime of flow instabilities. On the basis of these results, a temperature–strain rate window for hot working this material without microstructural defects is identified.
204 citations
TL;DR: The predictions that postural instability would precede the subjective symptoms of motion sickness in a fixed-base flight simulator and head motion among participants who later became sick was significantly greater than amongParticipants who did not become motion sick are argued to support the postural Stability Theory of Motion sickness.
Abstract: We evaluated the prediction that postural instability would precede the subjective symptoms of motion sickness in a fixed-base flight simulator Participants sat in a cockpit in a video projection dome and were exposed to optical flow that oscillated in the roll axis with exposure durations typical of flight simulation The frequencies of oscillation were those that characterize spontaneous postural sway during stance Head motion was measured prior to and during exposure to imposed optical flow Of 14 participants, 6 were classified as motion sick, either during or after exposure to the optical oscillation Prior to the onset of subjective symptoms, head motion among participants who later became sick was significantly greater than among participants who did not become motion sick We argue that the results support the postural instability theory of motion sickness Actual or potential applications include the prevention or mitigation of motion sickness in virtual environments
169 citations
TL;DR: A new, to the authors' knowledge, scene-based nonuniformity correction algorithm for array detectors that relies on the ability to register a sequence of observed frames in the presence of the fixed-pattern noise caused by pixel-to-pixel non uniformity.
Abstract: We describe a new, to our knowledge, scene-based nonuniformity correction algorithm for array detectors. The algorithm relies on the ability to register a sequence of observed frames in the presence of the fixed-pattern noise caused by pixel-to-pixel nonuniformity. In low-to-moderate levels of nonuniformity, sufficiently accurate registration may be possible with standard scene-based registration techniques. If the registration is accurate, and motion exists between the frames, then groups of independent detectors can be identified that observe the same irradiance (or true scene value). These detector outputs are averaged to generate estimates of the true scene values. With these scene estimates, and the corresponding observed values through a given detector, a curve-fitting procedure is used to estimate the individual detector response parameters. These can then be used to correct for detector nonuniformity. The strength of the algorithm lies in its simplicity and low computational complexity. Experimental results, to illustrate the performance of the algorithm, include the use of visible-range imagery with simulated nonuniformity and infrared imagery with real nonuniformity.
TL;DR: In this article, a detailed kinetic mechanism for hydrocarbon combustion is formulated to address the gas-phase chemistry of endothermic and conventional aviation fuels, and reaction paths are analysed for n-decane and kerosene premixed e ames, and the ability of themechanism to predictvarious premixed E ame features is assessed by comparison with experimental species proe les.
Abstract: Theintroductionofdetailedchemicalreactionmechanismsforaviationfuelsintocomplexmultidimensionale uid dynamics problems is not practical at the present time. Simplie ed reaction mechanisms that have been thoroughly evaluated must be developed to address specie c issues arising in realistic combustor cone gurations. The latter should be e rmly based on detailed mechanisms carefully evaluated against a wide range of experimental data. A detailed kinetic mechanism for hydrocarbon combustion is formulated to address the gas-phase chemistry of endothermic and conventional aviation fuels. Reaction paths are analysed for n-decane and kerosene premixed e ames, and the ability ofthemechanism to predictvarious premixed e ame featuresisassessed by comparison with experimental species proe les. Finally, the level of success achieved by the present kinetic model in the context of practical problems is discussed.
TL;DR: It is suggested that JP-8 penetration will not cause systemic toxicity because of low fluxes of all the components; and the absorption of aliphatic components into the skin may be a cause of skin irritation.
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01 Jan 2000
TL;DR: An overview of structures technology for future aerospace systems is given in this article, focusing on developments in component technologies that will improve the vehicle performance, advance the technology exploitation process, and reduce system life-cycle costs.
Abstract: An overview of structures technology for future aerospace systems is given. Discussion focuses on developments in component technologies that will improve the vehicle performance, advance the technology exploitation process, and reduce system life-cycle costs. The component technologies described are smart materials and structures, multifunctional materials and structures, affordable composite structures, extreme environment structures, flexible load bearing structures, and computational methods and simulation-based design. The trends in each of the component technologies are discussed and the applicability of these technologies to future aerospace vehicles is described.
TL;DR: In this article, an investigation of sonictransverse injection from circular and elliptic nozzles into a supersoniccrosse ow using planar Rayleigh/Mie scattering is reported.
Abstract: An investigation of sonictransverse injection from circular and elliptic nozzles into a supersoniccrosse ow using planar Rayleigh/Mie scattering is reported. Instantaneous images allow examination of the structural details, whereas ensemble-averaged images provide transverse penetration and lateral spread data for each jet. Standard deviation images produce information regarding the large-scale mixing/entrainment and reveal the mixing zones. Results show a highly three-dimensional near-e eld interaction dominated by shear-layer eddies and a counterrotating vortex pair. Ensemble-averaged results show that the elliptic jet spreads more rapidly in the lateral direction than the circular jet, cone rming that an axis-switching phenomenon is present. Near-e eld transverse penetration data collapse well with low-speed scaling conventions; however, the jet produced by the elliptic nozzle suffersa20%reductioninpenetrationcomparedto thecircularjet.Compressibilityleveldoesnotplaya signie cant roleintheaveragepenetrationorspreadofthesejets,althoughitstronglyaffectsthemixing/entrainmentandlargescale structure. Analysis of mixing potential from the standard deviation images indicates that the low and high convective Mach number Mc injection cases are signie cantly different; low Mc injection yields better large-scale mixing potential than high Mc injection regardless of the injector geometry.
01 Jan 2000
TL;DR: Radiation-induced alterations of factors related to bone remodeling and wound healing have a potential role in the pathogenesis of osteoradionecrosis.
Abstract: Objective To evaluate the factors involved in bone remodeling and wound healing that may be altered by radiation therapy. Design A prospective, controlled study of biochemical activity in vitro. Subjects MC3T3-E1 mouse osteoblasts. Interventions Cells were irradiated at 0, 2, 4, or 6 Gy. Specimens were harvested at 1, 7, 14, 28, and 42 days following irradiation for immunohistochemical analysis of transforming growth factor β 1 expression and transforming growth factor β 1 type I and II receptor expression. Collagen production was measured at 1, 7, 28, 35, and 49 days after irradiation. The effects of dexamethasone on collagen production and cell proliferation were also examined. Results Irradiated cells demonstrated decreased cell proliferation and a dose-dependent, sustained reduction in collagen production when compared with control cells. An increase in transforming growth factor β 1 type I and II receptor expression was noted in irradiated cells when compared with controls. Conclusion Radiation-induced alterations of factors related to bone remodeling and wound healing have a potential role in the pathogenesis of osteoradionecrosis.
TL;DR: In this paper, the tribological characteristics of WS 2 -nanocrystalline ZnO films have been investigated from ambient to 500°C using a ball-on-flat tribometer.
TL;DR: The Coin Cell Battery Imager as mentioned in this paper was used to record wideline 7 Li NMR spectra of the lithium ions that were electrochemically intercalated into three different types of carbon-based materials.
TL;DR: Berns et al.'s characterization technique is shown to yield the same accuracy as conventional characterization while reducing the number of measurements required, and to yield improved accuracy when correction for unintended light is needed but impractical.
Abstract: Three experiments were performed to evaluate methods for predicting the luminances and chromaticity coordinates produced by color CRT monitors, given known inputs. Linear and logarithmic versions of PLCC and PLVC, plus Berns, Motta, and Gorzynski's power function, were tested. Estimates are provided for the number of CRT measurement points needed to maximize each method's predictive accuracy. Correcting for unintended light from the monitor is shown to improve accuracy substantially for a case involving a seemingly small amount of light. Berns et al.'s characterization technique, which involves measuring the monitor's neutral point, is shown to yield the same accuracy as conventional characterization while reducing the number of measurements required, and to yield improved accuracy when correction for unintended light is needed but impractical. The accuracies of the predictive methods are compared and recommendations for their use are provided. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 90–104, 2000
TL;DR: Levofloxacin adequately penetrates a noninflamed prostate and should be evaluated for the therapy of prostatitis.
Abstract: Prostatitis has remained a pathological entity that is difficult to treat. Part of the difficulty revolves about the putative offending pathogens. For acute prostatitis, members of the Enterobacteriaceae, particularly Escherichia coli, play a central role, while intracellular pathogens such as Chlamydia are more frequently seen in chronic prostatitis. Consequently, a drug needs to be able to penetrate to this specialized site in both the acute and chronic infection forms of the disease and also have potent activity against the most common causative pathogens, both intracellular and extracellular. Levofloxacin has such an activity profile. We wished to document its ability to penetrate to the site of infection. Patients undergoing prostatectomies were administered 500 mg of levofloxacin orally every 24 h for 2 days prior to surgery, and then on the day of surgery, 500 mg was administered as an hour-long, constant-rate intravenous (i.v.) infusion. A set of blood samples was obtained as guided by stochastic optimal design theory. Prostate biopsy times were determined by randomizing subjects into one of four groups, based on the interval after the i.v. dose. All plasma and prostate drug concentrations were comodeled by a population modeling program, BigNPEM, implemented on the Cray T3E Supercomputer housed at the Supercomputer Center at the University of California at San Diego. Penetration was determined as the ratio of the area under the concentration-time curve (AUC) of levofloxacin in the prostate to the plasma levofloxacin AUC. When calculated from the mean population parameters, this penetration ratio was 2.96. We also performed a 1,000-subject Monte Carlo simulation from the mean parameter vector and covariance matrix. The mean penetration ratio here was 4.14 with a 95% confidence interval of 0.20 to 19.6. Over 70% of the population had a penetration ratio in excess of 1.0. Levofloxacin adequately penetrates a noninflamed prostate and should be evaluated for the therapy of prostatitis.
TL;DR: In this paper, Rayleigh scattering is used as a qualitative indication of gas temperature, thereby providing valuable information about the fluid near regions of local extinction, as indicated by well-defined breaks in the CH layer.
TL;DR: A modeling approach that can significantly speed up the dynamics simulation of large molecular systems is presented herein and allows for the elimination of the high‐frequency harmonic motion while capturing the low‐frequency anharmonic motion of interest.
Abstract: A modeling approach that can significantly speed up the dynamics simulation of large molecular systems is presented herein. A multigranular modeling approach, whereby different parts of the molecule are modeled at different levels of detail, is enabled by substructuring. Substructuring the molecular system is accomplished by collecting groups of atoms into rigid or flexible bodies. Body flexibility is modeled by a truncated set of body-based modes. This approach allows for the elimination of the high-frequency harmonic motion while capturing the low-frequency anharmonic motion of interest. This results in the use of larger integration step sizes, substantially reducing the computational time required for a given dynamic simulation. The method also includes the use of a multiple time scale (MTS) integration scheme. Speed increases of 5- to 30-fold over atomistic simulations have been realized in various applications of the method. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 159–184, 2000
01 Sep 2000
TL;DR: The trend in both military and commercial markets for greater affordability has prompted the electromechanical designer toward higher speed and higher operating temperature devices as mentioned in this paper.New magnetic materials are essential for the success of many of these power generation, distribution, and utilization systems.
Abstract: The trend in both military and commercial markets for greater affordability has prompted the electromechanical designer toward higher speed and higher operating temperature devices. New magnetic materials are essential for the success of many of these power generation, distribution, and utilization systems. This manuscript briefly describes some of the applications for advanced high temperature magnets.
TL;DR: In this paper, the evolution of microstructure with deposition parameters in pulsed laser deposited ZnO thin films, specifically targeted for friction and wear applications, was described by high resolution scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD).
TL;DR: In this article, the AGARD 445.6 standard aeroelastic wing configuration using a fully implicit, aero-elastic Navier-Stokes solver coupled to a general, linear, second-order structural solver is presented.
Abstract: Flutter computations are presented for the AGARD 445.6 standard aeroelastic wing configuration using a fully implicit, aeroelastic Navier-Stokes solver coupled to a general, linear, second-order structural solver. This solution technique realizes implicit coupling between the fluids and structures using a subiteration approach. Results are presented for two Mach numbers, M∞ = 0.96 and 1.141. The computed flutter predictions are compared with experimental data and with previous Navier-Stokes computations for the same case. Predictions of the flutter point for the M∞ = 0.96 case agree well with experimental data. At the higher Mach number, M∞ = 1.141, the present computations overpredict the flutter point but are consistent with other computations for the same case. The sensitivity of computed solutions to grid resolution, the number of modes used in the structural solver, and transition location is investigated. A comparison of computations using a standard second-order accurate central-difference scheme and a third-order upwind-biased scheme is also made.
TL;DR: In this article, the microstructure and chemistry within ZnO are controlled to provide low-friction and long-life coatings (e.g., µ=0.1−0.2, 1M+ sliding cycles).
Abstract: Oxide coatings have the potential to lubricate over a wide range of environmental conditions. However, oxides are typically brittle, form abrasive wear debris, and have high friction. ZnO is no exception; hot-pressed 1–2 µm ZnO has a friction coefficient of about 0.6 and causes extensive wear on steel counterfaces. Microstructural engineering may be used to permit plastic deformation and the formation of lubricious transfer films. The work presented here focuses on controlling the microstructure and chemistry within ZnO to provide low-friction and long-life coatings (e.g., µ=0.1−0.2, 1M+ sliding cycles). Coatings having a (0001) columnar texture with good crystallinity along the c-axis wear quickly and generate substantial wear debris. Depositions that create a (0001) texture with a mosaic substructure within the columns deform plastically. Here, nanocrystalline structures may enhance grain boundary sliding and contribute to plastic deformation and low friction. Dislocation motion within ZnO is enhanced by oxygen adsorption, which may further reduce friction by lowering shear strength. In addition, it is likely that defects arising from oxygen deficiency and the high surface-to-volume ratio of nanostructures, promote adsorption of water and/or oxygen. The adsorbed species can reduce friction through passivation of dangling or strained bonds. The complex interaction of mechanical and surface chemical effects result in millions of dry sliding cycles on nanostructured coatings in 50% RH air. In addition, the coatings have low friction in vacuum. Coating characterization and performance are discussed and a mechanism to explain the tribological properties is proposed.
TL;DR: In this paper, the authors used strain gages to investigate variations in thermal expansion coefficient (CTE) with damage of two representative aerospace structural materials, AS4/3501-6 and XN-70/RS3.
TL;DR: In this article, a powder-metallurgically processed 7093/SiC/15p discontinuously reinforced aluminum (DRA) composite in different heat-treatment conditions, to determine the influence of matrix characteristics on the composite response.
Abstract: Mechanical tests were performed on a powder-metallurgically processed 7093/SiC/15p discontinuously reinforced aluminum (DRA) composite in different heat-treatment conditions, to determine the influence of matrix characteristics on the composite response. The work-hardening exponent and the strain to failure varied inversely to the strength, similar to monolithic Al alloys, and this dependence was independent of the dominant damage mode. The damage consisted of SiC particle cracks, interface and near-interface debonds, and matrix rupture inside intense slip bands. Fracture surfaces revealed particle fracture-dominated damage for most of the heat-treatment conditions, including an overaged (OA) condition that exhibited a combination of precipitates at the interface and a precipitate-free zone (PFZ) in the immediate vicinity. In the highly OA conditions and in a 450 °C as-rolled condition, when the composite strength became less than 400 MPa, near-interface matrix rupture became dominant. A combination of a relatively weak matrix and a weak zone around the particle likely contributed to this damage mode over that of particle fracture. Fracture-toughness tests show that it is important to maintain a proper geometry and testing procedure to obtain valid fracture-toughness data. Overaged microstructures did reveal a recovery of fracture toughness as compared to the peak-aged (PA) condition, unlike the lack of toughness recovery reported earlier for a similar 7XXX (Al-Zn-Cu-Mg)-based DRA. The PA material exhibited extensive localization of damage and plasticity. The low toughness of the DRA in this PA condition is explored in detail, using fractography and metallography. The damage and fracture micromechanisms formed the basis for modeling the strength, elongation, toughness, and damage, which are described in Part II of this work.
TL;DR: In this article, both mono-and multiple-functionalized C60 derivatives were synthesized and studied for their photophysical properties, including absorption spectra and absorptivities, and the fluorescence quantum yields were quantitatively determined using a near-infrared sensitive emission spectrometer.
Abstract: Mono- and multiple-functionalized C60 derivatives were synthesized and studied for their photophysical properties. Electronic absorption spectra and absorptivities of the C60 derivatives in solution were measured and compared. By recording the fluorescence spectra using a near-infrared-sensitive emission spectrometer, we quantitatively determined fluorescence quantum yields of the C60 derivatives. For the mono-functionalized C60 derivatives, the compound with a [5,6]-open fulleroid addition pattern on the fullerene cage appeared to be considerably less fluorescent than those with a [6,6]-closed cage addition pattern. Despite the disturbance of the electronic structure via multiple additions to the fullerene cage, the multiple-functionalized C60 derivatives exhibited no dramatic changes in fluorescence quantum yields in comparison with the mono-functionalized C60 derivatives. The fluorescence lifetimes of the C60 derivatives, obtained using the time-correlated single photon-counting technique, were all in ...