Showing papers on "Absorption (electromagnetic radiation) published in 2006"

Light Absorption by Carbonaceous Particles: An Investigative Review

Abstract: The optical properties of the light-absorbing, carbonaceous substance often called “soot,” “black carbon,” or “carbon black" have been the subject of some debate. These properties are necessary to model how aerosols affect climate, and our review is targeted specifically for that application. We recommend the term light-absorbing carbon to avoid conflict with operationally based definitions. Absorptive properties depend on molecular form, particularly the size of sp 2-bonded clusters. Freshly-generated particles should be represented as aggregates, and their absorption is like that of particles small relative to the wavelength. Previous compendia have yielded a wide range of values for both refractive indices and absorption cross section. The absorptive properties of light-absorbing carbon are not as variable as is commonly believed. Our tabulation suggests a mass-normalized absorption cross section of 7.5 ± 1.2 m2/g at 550 nm for uncoated particles. We recommend a narrow range of refractive indices for s...

Surface enhanced vibrational spectroscopy

Abstract: The nature and properties of surface-enhanced vibrational spectra of molecules adsorbed on surfaces that can enhance the absorption and the emission of electromagnetic radiation are discussed. Examples of surface-enhanced resonant Raman scattering, surface-enhanced Raman scattering in the near-infrared and surface-enhanced infrared are given. The rough surfaces used are metal island films coated with a nanometric organic film using the Langmuir-Blodgett technique or deposited by vacuum evaporation.

Synthesis and photovoltaic properties of two-dimensional conjugated polythiophenes with bi(thienylenevinylene) side chains.

Abstract: Three two-dimensional (2-D) conjugated polythiophenes with bi(thienylenevinylene) side chains (biTV-PTs), P1, P2, and P3, were designed and synthesized for application in polymer solar cells. The absorption spectral, electrochemical, and photovoltaic properties of the biTV-PTs were investigated and compared with those of poly(3-hexylthiophene) (P3HT). The biTV-PTs show a broad absorption band from 350 to 650 nm; especially, the absorption spectrum of P3 displays a broad plateau and much stronger absorbance than that of P3HT in the wavelength range from 350 to 480 nm. Cyclic voltammograms reveal that the onset oxidation and reduction potentials of the biTV-PTs positively shifted by ca. 0.2 V in comparison with those of P3HT, indicating that the HOMO energy level of the biTV-PTs is ca. 0.2 eV lower than that of P3HT. Polymer solar cells (PSCs) were fabricated based on the blend of the polymers and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-61 (PCBM) with a weight ratio of 1:1. The open circuit voltage of ...

Optical properties of deep glacial ice at the South Pole

Abstract: We have remotely mapped optical scattering and absorption in glacial ice at the South Pole for wavelengths between 313 and 560 nm and depths between 1100 and 2350 m. We used pulsed and continuous light sources embedded with the AMANDA neutrino telescope, an array of more than six hundred photomultiplier tubes buried deep in the ice. At depths greater than 1300 m, both the scattering coefficient and absorptivity follow vertical variations in concentration of dust impurities, which are seen in ice cores from other Antarctic sites and which track climatological changes. The scattering coefficient varies by a factor of seven, and absorptivity (for wavelengths less than ∼450 nm) varies by a factor of three in the depth range between 1300 and 2300 m, where four dust peaks due to stadials in the late Pleistocene have been identified. In our absorption data, we also identify a broad peak due to the Last Glacial Maximum around 1300 m. In the scattering data, this peak is partially masked by scattering on residual air bubbles, whose contribution dominates the scattering coefficient in shallower ice but vanishes at ∼1350 m where all bubbles have converted to nonscattering air hydrates. The wavelength dependence of scattering by dust is described by a power law with exponent -0.90 ± 0.03, independent of depth. The wavelength dependence of absorptivity in the studied wavelength range is described by the sum of two components: a power law due to absorption by dust, with exponent -1.08 ± 0.01 and a normalization proportional to dust concentration that varies with depth; and a rising exponential due to intrinsic ice absorption which dominates at wavelengths greater than ∼500 nm. Copyright 2006 by the American Geophysical Union.

Limitations in the enhancement of visible light absorption due to mixing state

Abstract: [1] Absorption by light-absorbing carbon (LAC) particles increases when the carbon is mixed with other material, and this change affects climate forcing. We investigate this increase theoretically over a realistic range of particle sizes. Perfect mixing at the molecular level often overestimates absorption. Assuming that LAC is coated by a concentric shell of weakly absorbing material, we calculate absorption by a range of realistic particle sizes and identify regimes in which absorption behaves similarly. We provide fits to amplification in five regions: (1) small cores and (2) intermediate cores, both with large shells; (3) small to intermediate cores with intermediate shells; (4) cores with growing shells; and (5) intermediate to large cores with large shells. Amplification in region 1 is highest but is physically implausible. Amplification in region 5 is constant at about 1.9 and represents an asymptote for particles with broad size distributions. Because absorption by aggregates is amplified by about 1.3 above spherical particles, and that factor is lost when particles are coated, we suggest that absorption by aged aerosol is about 1.5 times greater than that of fresh aerosol. The rate at which particles acquire sufficient coating to increase their original diameter by 60% is important in determining total absorption during their atmospheric lifetimes. Fitted amplification factors are not very sensitive to assumed refractive index of LAC and can be used even in simple models.

Broadband Cavity Ringdown Spectroscopy for Sensitive and Rapid Molecular Detection

Abstract: We demonstrate highly efficient cavity ringdown spectroscopy in which a broad-bandwidth optical frequency comb is coherently coupled to a high-finesse optical cavity that acts as the sample chamber. 125,000 optical comb components, each coupled into a specific longitudinal cavity mode, undergo ringdown decays when the cavity input is shut off. Sensitive intracavity absorption information is simultaneously available across 100 nanometers in the visible and near-infrared spectral regions. Real-time, quantitative measurements were made of the trace presence, the transition strengths and linewidths, and the population redistributions due to collisions and the temperature changes for molecules such as C2H2, O2, H2O, and NH3.

Fabrication and microwave absorption of carbon nanotubes/CoFe2O4 spinel nanocomposite

Abstract: A large-scale carbon nanotube∕CoFe2O4 (CNTs∕CoFe2O4) spinel nanocomposite has been fabricated by a chemical vapor deposition method using CoFe2O4 nanoparticles as catalysts. A uniform mixture of CNTs and CoFe2O4 nanoparticles was obtained simultaneously. The structure and chemical composition of the product were investigated using various techniques, such as x-ray diffraction, high-resolution transmission electron microscopy, and electron energy loss spectroscopy. It was found that the particles functionalized on CNTs were cubic phase CoFe2O4. Microwave absorption of the CNT∕CoFe2O4 nanocomposites at 2–18 GHz is evidently enhanced, as compared with that of both pure CNTs and CoFe2O4 nanoparticles. The enhancement mechanism is discussed based on magnetization hysteresis loop measurement and electromagnetic theory.

The modified Beer–Lambert law revisited

Abstract: The modified Beer–Lambert law (MBLL) is the basis of continuous-wave near-infrared tissue spectroscopy (cwNIRS). The differential form of MBLL (dMBLL) states that the change in light attenuation is proportional to the changes in the concentrations of tissue chromophores, mainly oxy- and deoxyhaemoglobin. If attenuation changes are measured at two or more wavelengths, concentration changes can be calculated. The dMBLL is based on two assumptions: (1) the absorption of the tissue changes homogeneously, and (2) the scattering loss is constant. It is known that absorption changes are usually inhomogeneous, and therefore dMBLL underestimates the changes in concentrations (partial volume effect) and every calculated value is influenced by the change in the concentration of other chromophores (cross-talk between chromophores). However, the error introduced by the second assumption (cross-talk of scattering changes) has not been assessed previously. An analytically treatable special case (semi-infinite, homogeneous medium, with optical properties of the cerebral cortex) is utilized here to estimate its order of magnitude. We show that the per cent change of the transport scattering coefficient and that of the absorption coefficient have an approximately equal effect on the changes of attenuation, and a 1% increase in scattering increases the estimated concentration changes by about 0.5 µM.

Terahertz dielectric properties of polymers

Abstract: The terahertz dielectric properties of polymers were characterized by transmission terahertz time domain spectroscopy (THz-TDS) in the frequency range extending from 0.2 to 3.0 THz. The terahertz absorption spectra, the refractive indices and the dielectric functions of various polymer materials were measured and compared. The variation of the refractive index of the polymers was less than 6 %, ranging from 1.4 to 1.8, within the investigated frequency range, but the absorption properties of the polymers showed very different frequency-dependent behaviors. The loss mechanism for terahertz radiation in polymers is discussed by correlating the absorption coefficients and the loss tangents (tan {delta}) of the materials.

Autonomous artificial nanomotor powered by sunlight

Abstract: Light excitation powers the reversible shuttling movement of the ring component of a rotaxane between two stations located at a 1.3-nm distance on its dumbbell-shaped component. The photoinduced shuttling movement, which occurs in solution, is based on a “four-stroke” synchronized sequence of electronic and nuclear processes. At room temperature the deactivation time of the high-energy charge-transfer state obtained by light excitation is ≈10 μs, and the time period required for the ring-displacement process is on the order of 100 μs. The rotaxane behaves as an autonomous linear motor and operates with a quantum efficiency up to ≈12%. The investigated system is a unique example of an artificial linear nanomotor because it gathers together the following features: (i) it is powered by visible light (e.g., sunlight); (ii) it exhibits autonomous behavior, like motor proteins; (iii) it does not generate waste products; (iv) its operation can rely only on intramolecular processes, allowing in principle operation at the single-molecule level; (v) it can be driven at a frequency of 1 kHz; (vi) it works in mild environmental conditions (i.e., fluid solution at ambient temperature); and (vii) it is stable for at least 103 cycles.

Characterization and luminescence properties of Sr2Si5N8:Eu2+ phosphor for white light-emitting-diode illumination

Abstract: Eu2+-doped ternary nitride phosphor, Sr2Si5N8:Eu2+, was prepared by the carbothermal reduction and nitridation method. The Rietveld refinement analysis showed that the single phase products were obtained. Two main absorption bands were observed on the diffuse reflection spectra peaking at about 330 and 420nm, so that the resultant phosphor can be effectively excited by InGaN light-emitting diodes. The emission peak position of (Sr1−xEux)2Si5N8:Eu2+ series varied from 618to690nm with increasing Eu2+ ion concentration. The redshift behavior of the emission band was discussed on the basis of the configuration coordination model.

Optical amplification of photothermal therapy with gold nanoparticles and nanoclusters

Abstract: Recently, several groups (Anderson, Halas, Zharov, and their co-workers, 2003; El-Sayed and co-workers, 2006) demonstrated, through pioneering results, the great potential of photothermal (PT) therapy for the selective treatment of cancer cells, bacteria, viruses, and DNA targeted with gold nanospheres, nanoshells, nanorods, and nanosphere clusters. However, the current understanding of the relationship between the nanoparticle/cluster parameters (size, shape, particle/cluster structure, etc) and the efficiency of PT therapy is limited. Here, we report theoretical simulations aimed at finding the optimal single-particle and cluster structures to achieve its maximal absorption, which is crucial for PT therapeutic effects. To characterize the optical amplification in laser-induced thermal effects, we introduce relevant parameters such as the ratio of the absorption cross section to the gold mass of a single-particle structure and absorption amplification, defined as the ratio of cluster absorption to the total absorption of non-interacting particles. We consider the absorption efficiency of single nanoparticles (gold spheres, rods, and silica/gold nanoshells), linear chains, 2D lattice arrays, 3D random volume clusters, and the random aggregated N-particle ensembles on the outer surface of a larger dielectric sphere, which mimic aggregation of nanosphere bioconjugates on or within cancer cells. The cluster particles are bare or biopolymer-coated gold nanospheres. The light absorption of cluster structures is studied by using the generalized multiparticle Mie solution and the T-matrix method. The gold nanoshells with (silica core diameter)/(gold shell thickness) parameters of (50–100)/(3–8) nm and nanorods with minor/major sizes of (15–20)/(50–70) nm are shown to be more efficient PT labels and sensitizers than the equivolume solid single gold spheres. In the case of nanosphere clusters, the interparticle separations and the short linear-chain fragments are the main structural parameters determining the absorption efficiency and its spectral shifting to the red. Although we have not found a noticeable dependence of absorption amplification on the cluster sphere size, 20–40 nm particles are found to be most effective, in accordance with our experimental observations. The long-wavelength absorption efficiency of random clusters increases with the cluster particle number N at small N and reveals a saturation behaviour at N>20.

Absorption and scattering microscopy of single metal nanoparticles

Abstract: Several recently developed detection techniques opened studies of individual metal nanoparticles (1-100 nm in diameter) in the optical far field. Eliminating averaging over the broad size and shape distributions produced by even the best of current synthesis methods, these studies hold great promise for gaining a deeper insight into many of the properties of metal nanoparticles, notably electronic and vibrational relaxation. All methods are based on detection of a scattered wave emitted either by the particle itself, or by its close environment. Direct absorption and interference techniques rely on the particle's scattering and have similar limits in signal-to-noise ratio. The photothermal method uses a photo-induced change in the refractive index of the environment as an additional step to scatter a wave with a different wavelength. This leads to a considerable improvement in signal-to-background ratio, and thus to a much higher sensitivity. We briefly discuss and compare these various techniques, review the new results they generated so far, and conclude on their great potential for nanoscience and for single-molecule labelling in biological assays and live cells.

Extension of wavelength-modulation spectroscopy to large modulation depth for diode laser absorption measurements in high-pressure gases

Abstract: Tunable diode laser absorption measurements at high pressures by use of wavelength-modulation spectroscopy (WMS) require large modulation depths for optimum detection of molecular absorption spectra blended by collisional broadening or dense spacing of the rovibrational transitions. Diode lasers have a large and nonlinear intensity modulation when the wavelength is modulated over a large range by injection-current tuning. In addition to this intensity modulation, other laser performance parameters are measured, including the phase shift between the frequency modulation and the intensity modulation. Following published theory, these parameters are incorporated into an improved model of the WMS signal. The influence of these nonideal laser effects is investigated by means of wavelength-scanned WMS measurements as a function of bath gas pressure on rovibrational transitions of water vapor near 1388 nm. Lock-in detection of the magnitude of the 2f signal is performed to remove the dependence on detection phase. We find good agreement between measurements and the improved model developed for the 2f component of the WMS signal. The effects of the nonideal performance parameters of commercial diode lasers are especially important away from the line center of discrete spectra, and these contributions become more pronounced for 2f signals with the large modulation depths needed for WMS at elevated pressures.

Emission Factors and Real-Time Optical Properties of Particles Emitted from Traditional Wood Burning Cookstoves

Abstract: It is estimated that the combustion of biofuel generates 20% of all carbonaceous aerosols, yet these particles are studied less than those of other common sources. We designed and built a portable battery-operated emission-sampling cart to measure the real-time optical properties and other emission characteristics of biofuel cookstoves. In a field study in Honduras, we measured emission factors averaging 8.5 g/kg, higher than those found in previous laboratory studies. Strong flaming events emitted very dark particles with the optical properties of black particles. The elemental carbon to total carbon ratios ranged from 0.07 to 0.64, confirming that high elemental carbon fractions can be emitted from biofuel combustion and may not be used to distinguish fossil-fuel from biofuel sources when cooking is the dominant usage. Absorption Angstrom exponents, representing the dependence of absorption on wavelength, ranged from 1 (black) to 5 (yellow). Strongly absorbing particles with absorption inversely dependent on wavelength were emitted separately from particles with weak absorption and strong wavelength dependence; the latter probably contained conjugated aromatic compounds. Because combustion occurs in distinct phases, different types of carbonaceous aerosols from biofuel combustion are externally mixed at emission and may have different atmospheric fates.

Collision-induced Absorption in Gases

Abstract: 1. Introduction 2. Recapitulation 3. Experimental results 4. Induced dipoles 5. Theory: monatomic gas mixtures 6. Theory: molecular gases 7. Related Topics References Index.

Poly(2,7-carbazole) and perylene tetracarboxydiimide: a promising donor/acceptor pair for polymer solar cells

Abstract: A highly soluble polycarbazole (PCz) has been synthesized, and used as a donor material with perylene tetracarboxydiimide (PDI) as an acceptor and light harvesting material in bulk-heterojunction solar cells. This donor/acceptor (D/A) pair shows a broad absorption fit within the solar spectrum, and balanced potential levels for charge separation at the D/A interface. The best photovoltaic device exhibits a high external quantum efficiency (EQE) of 16% at 490 nm and a power efficiency of 0.6% under illumination with solar light. The morphology of PCz/PDI films studied by SEM showed the formation of a favorable micro-phase separation, which is important in obtaining high efficiency. Incorporation of poly(3-hexyl)thiophene (P3HT) instead of PCz as donor produced a much lower Voc and thus a lower efficiency in solar cells.

Implementation of real-time multiple reflection and Fresnel absorption of laser beam in keyhole

Abstract: A computational analysis of laser keyhole welding is achieved. The main driving force to make the molten pool as a narrow and deep keyhole is the recoil pressure induced by evaporation of the material. Also, the multiple reflection effect on the keyhole wall plays an important role in making the keyhole deeper and raising its total energy absorption rate. Multiple reflection and Fresnel absorption are implemented simultaneously with the proposed ray tracing technique in a discrete grid cell system during the simulation for every single time step. In particular, the Fresnel absorption model is chosen as an energy transfer mechanism from laser beam to workpiece. With all the governing equations including continuity, momentum and energy equation, the VOF method is adopted to trace the free surface of the molten pool. Simulation results are compared with the experimental ones to verify its validity. A pulsed Nd : YAG laser was used for keyhole welding experiments on mild steel plates of 7 mm thickness. It was observed that the generated keyhole maintains its solidified shape without any closing phenomenon both in the experiments and in the simulations.

Aerosol Absorption Measurement using Photoacoustic Spectroscopy: Sensitivity, Calibration, and Uncertainty Developments

Abstract: Light absorption by aerosols is one of the most uncertain parameters associated with the direct and indirect aerosol effects on climate and is one of the most difficult quantities to measure This article describes the development of a sensitive method of measuring aerosol absorption at 532 nm with excellent time response (detection limit: 008 Mm−1, 60 second average) using photoacoustic absorption spectroscopy An accurate calibration method (accuracy of 1–2%) at atmospherically relevant absorption levels and independent validation of the photoacoustic technique is presented An upper limit to the instrument precision for aerosol absorption measurement is ∼6% (2σ, 30 sec) while instrument accuracy is calculated to be ∼5% A standard for aerosol absorption measurement techniques using well characterized absorbing aerosol is also proposed

Visible Light Absorption by Various Titanium Dioxide Specimens

Abstract: A set of heat-induced and photoinduced absorption spectra of various compositions of Degussa P25 TiO2 and different polymers has been examined The spectra are described as the sum of overlapping absorption bands (ABs) with maxima at 290 eV (427 nm, AB1), 255 eV (486 nm, AB2), and 205 eV (604 nm, AB3); the spectra correlate entirely with the experimentally observed absorption spectra after the reduction of TiO2 Absorption spectra of visible-light-active TiO2 photocatalysts reported recently in the literature have also been analyzed Relatively narrow absorption spectra are very similar and independent of the method of photocatalyst preparation The average absorption spectrum can be described reasonably well by the sum of the two absorption bands AB1 and AB2 It is argued that visible light activation of TiO2 specimens (anion-doped or otherwise) implicates defects associated with oxygen vacancies that give rise to color centers displaying these absorption bands and not to a narrowing of the original band gap of TiO2 (EBG approximately 32 eV, anatase) through mixing of dopant and oxygen states, as has been suggested recently in the literature

Photoinduced charge transfer between CdSe nanocrystal quantum dots and Ru-polypyridine complexes.

Abstract: In this communication, we demonstrate a new approach to sensitization of Ru−polypyridine complexes by using semiconductor nanocrystal quantum dots (NQDs). When mixed in solution, the complexes functionalized by carboxylic groups adsorb onto the surface of the NQDs. Excitation of NQDs by 400 nm light leads to fast, 5 ps hole transfer from the photoexcited NQDs to the surface-adsorbed complexes. This result indicates that Ru complexes can be sensitized by CdSe NQDs, which opens interesting opportunities for designing new types of photocatalytic materials for solar energy conversion applications. These materials will take advantage of broad size-controlled absorption spectra and large extinction coefficients of NQDs as well as the unique property of NQDs to respond to absorption of a single photon by producing multiple electron−hole pairs.

Linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a quantum box with finite confining potential

Abstract: In this work, both the intersubband optical absorption coefficients and the refractive index changes are calculated exactly in a quantum box. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using the compact-density matrix approach. Numerical results are presented for typical GaAs/AlxGa1−x As quantum box system. The linear, third-order nonlinear and total absorption and refractive index changes are investigated as a function of the incident optical intensity and structure parameters such as box-edge length and stoichiometric ratio. Our results show that both the incident optical intensity and the structure parameters have a great effect on the total absorption and refractive index changes.

Oxygen vacancy in monoclinic HfO2: A consistent interpretation of trap assisted conduction, direct electron injection, and optical absorption experiments

Abstract: The authors calculate energy levels associated with the oxygen vacancy in monoclinic HfO2 using a hybrid density functional which accurately reproduces the experimental band gap. The most stable charge states are obtained for varying Fermi level in the HfO2 band gap. To compare with measured defect levels, they determine total energy differences specific to the considered experiment. Their results show that the oxygen vacancy can consistently account for the defect levels observed in (Poole-Frenkel-type) trap assisted conduction, direct electron injection, and optical absorption experiments.

Retrievals of a size parameter for phytoplankton and spectral light absorption by colored detrital matter from water‐leaving radiances at SeaWiFS channels in a continental shelf region off Brazil

Abstract: Many efforts are currently oriented toward extracting more information from ocean color than the chlorophyll a concentration. Among biological parameters potentially accessible from space, estimates of phytoplankton cell size and light absorption by colored detrital matter (CDM) would lead to an indirect assessment of major components of the organic carbon pool in the ocean, which would benefit oceanic carbon budget models. We present here 2 procedures to retrieve simultaneously from ocean color measurements in a limited number of bands, magnitudes, and spectral shapes for both light absorption by CDM and phytoplankton, along with a size parameter for phytoplankton. The performance of the 2 procedures was evaluated using different data sets that correspond to increasing uncertainties: (1) measured absorption coefficients of phytoplankton, particulate detritus, and colored dissolved organic matter (CDOM) and measured chlorophyll a concentrations and (2) SeaWiFS upwelling radiance measurements and chlorophyll a concentrations estimated from global algorithms. In situ data were acquired during 3 cruises, differing by their relative proportions in CDM and phytoplankton, over a continental shelf off Brazil. No local information was introduced in either procedure, to make them more generally applicable. Over the study area, the absorption coefficient of CDM at 443 nm was retrieved from SeaWiFS radiances with a relative root mean square error (RMSE) of 33%, and phytoplankton light absorption coefficients in SeaWiFS bands (from 412 to 510 nm) were retrieved with RMSEs between 28% and 33%. These results are comparable to or better than those obtained by 3 published models. In addition, a size parameter of phytoplankton and the spectral slope of CDM absorption were retrieved with RMSEs of 17% and 22%, respectively. If these methods are applied at a regional scale, the performances could be substantially improved by locally tuning some empirical relationships.

The optical properties of mineral suspended particles: A review and synthesis

Abstract: Small mineral particles suspended in the sea are excellent at reflecting light and show up well in visible band satellite images. In order to make quantitative estimates of the particle concentration, and its effect on the penetration of sunlight into the sea, it is necessary to know how the absorption, scattering and backscattering coefficients of these inorganic particles change with concentration, the nature of the particles, and with wavelength. In this paper, observations from the literature are supplemented with a data set from the Irish Sea. The concentration-specific absorption coefficient of mineral particles am∗ is generally found to decrease exponentially with wavelength towards (in our data) a constant non-zero value in the red. Specific scattering coefficients show a tendency to decrease from the open ocean into energetic shelf seas and estuaries, but then to increase again within shelf seas as turbulent energy increases. The variation of specific scattering with turbulent energy in the Irish Sea is consistent with particle size scaling with the Kolmogorov microscale. Colour ratios (the ratio of two reflection coefficients) are less sensitive to variations in scattering, and we suggest that a combination of satellite measurements of brightness and colour in water with high mineral suspended sediment content will produce (1) a better estimate of concentration and (2) information on the variation of specific scattering.

Relationship between Two-Photon Absorption and the π-Conjugation Pathway in Porphyrin Arrays through Dihedral Angle Control

Abstract: Recently, covalently linked or self-assembled porphyrin array systems have attracted much attention for their enhanced two-photon absorption (TPA) behaviors. In this study, we have investigated the TPA properties of various dihedral angle controlled, directly linked porphyrin dimers and arrays to elucidate the relationship between the π-conjugation pathway and TPA properties. We have demonstrated a strong correlation between π-conjugation (aromaticity) and TPA properties in porphyrin assemblies.