To understand the properties of light-sensitive compounds used in optical limiters having photoinduced charge transfer mechanisms, we have investigated the photophysics of a series of di(2-thienyl-3, 3’-butyl)polyenes. Spectroscopic measurements, including UV/Vis, fluorescence, fluorescence lifetimes, fluorescence quantum yields, triplet state lifetime, solvent effects and two-photon absorption coefficient were obtained as a function of the number of double bonds(n = 1-5). Trends in the data reflected the ordering, energy gap between and mixing of 1 B u * and 1 A g * excited state configurations.

We have studied dispersion of the cubic nonlinear optical properties of organic and organometallic nonlinear absorbers. The results indicate that a multitude of excited states may be contributing to the resonances seen in the real and imaginary part of the complex hyperpolarizability. Attempts to understand the relation between the real and imaginary part of the hyperpolarizability in terms of a Kramers-Kronig transform are undertaken.

There is much interest in nonlinear absorbing chromophores for applications in photonics, nanophotonics and biophotonics. We have performed studies of dispersion of the nonlinear absorption cross sections and the refractive nonlinearities of organic and organometallic nonlinear chromophores using the technique of Z-scan, with a tunable amplified femtosecond laser system. Z-scan is less sensitive than the popular technique of two-photon induced fluorescence but has advantages of being suitable for non-fluorescent substances and providing information on both absorptive and refractive nonlinearities. We have analysed the experimental results in terms of simple models and using the Kramers-Kronig transformation as shown in this paper for Coumarine 307 and an organometallic dendrimer. The dispersion curves are often dominated by two-photon resonances but inclusion of other nonlinear mechanisms seems to be necessary for better understanding of their features.

A comprehensive photophysical study of the linear and nonlinear absorption properties has been carried out on two series of two-photon absorbing dyes to gain insight into how structure-property relationships influence observed nonlinear absorption. The materials studied consist of an electron accepting benzothiazole group connected to an electron donating diphenylamine via a fluorene bridging group. Two series differ from each other by the addition of one phenyl group and for each series one-arm (dipolar, AF240 and AF270), two-arm (quadrupolar, AF287 and AF295), and three-arm (octupolar, AF350 and AF380) versions were studied. Overall the AF240 series exhibits higher intrinsic two-photon absorption (TPA) cross-sections than the AF270 series as well as enhanced nanosecond nonlinear absorption, with an increase with number of branches. The enhanced nanosecond nonlinearity is understood by taking into account the contribution from the singlet and triplet excited states and was verified by a two-photon assisted excited-state absorption model that satisfactorily predicts the nonlinear absorption of the chromophores.

To explore the photophysics of platinum acetylide chromophores with strong two-photon absorption cross-sections, we have investigated the synthesis and spectroscopic characterization of a series of platinum acetylide complexes that feature highly pi-conjugated ligands substituted with pi-donor or -acceptor moieties. The molecules (numbered 1-4) considered in the present work are analogs of bis(phenylethynyl)bis(tributylphosphine)platinum(II) complexes. Molecule 1 carries two alkynyl-benzothiazolylfluorene ligands, and molecule 2 has two alkynyl-diphenylaminofluorene ligands bound to the central platinum atom. Compounds 3 and 4 possess two dihexylaminophenyl substituents at their ends and differ by the number of platinum atoms in the oligomer "core" (one vs two in 3 and 4, respectively). The ligands have strong effective two-photon absorption cross-sections, while the heavy metal platinum centers give rise to efficient intersystem crossing to long-lived triplet states. Ultrafast transient absorption and emission spectra demonstrate that one-photon excitation of the chromophores produces an S1 state delocalized across the two conjugated ligands, with weak (excitonic) coupling through the platinum centers. Intersystem crossing occurs rapidly (Kisc approximately 1011 s-1) to produce the T1 state, which is possibly localized on a single conjugated fluorenyl ligand. The triplet state is strongly absorbing (epsilonTT > 5 x 104 M-1 cm-1), and it is very long-lived (tau > 100 micro s). Femtosecond pulses were used to characterize the two-photon absorption properties of the complexes, and all of the chromophores are relatively efficient two-photon absorbers in the visible and near-infrared region of the spectrum (600-800 nm). The complexes exhibit maximum two-photon absorption at a shorter wavelength than 2lambda for the one-photon band, consistent with the dominant two-photon transition arising from a two-photon-allowed gerade-gerade transition. Nanosecond transient absorption experiments carried out on several of the complexes with excitation at 803 nm confirm that the long-lived triplet state can be produced efficiently via a sequence involving two-photon excitation to produce S1, followed by intersystem crossing to produce T1.

beta,meso,beta-Fused porphyrin oligomers have many attractive photophysical features such as strong absorption in the near-IR at wavelengths greater than 1000 nm, and high two-photon cross sections. However their ultrafast S(1)-S(0) deactivation (k(d) > 10(11) s(-1)) limits potential applications. We have synthesised a deuterated fused porphyrin dimer to test whether deuteration influences the rate of non-radiative deactivation. An efficient synthetic strategy was developed, starting with deuteration of dipyrromethane. Deuteration of the zinc porphyrin dimer does not affect its fluorescence quantum yield in CD(2)Cl(2)(Phi(fD)/Phi(fH)= 1.00 +/- 0.05). This implies that the ultrafast non-radiative deactivation is not simply a consequence of the small S(1)-S(0) energy gap. Comparison with other conjugated porphyrin oligomers confirms that the deactivation rate in the edge-fused oligomers is faster than would be expected from the energy gap law. This result indicates that it should be possible to create near-IR dyes with similar S(1)-S(0) energy gaps to the beta,meso,beta-fused porphyrin oligomers but with slower rates of S(1)-S(0) decay.

Polymer dielectric films fabricated by plasma enhanced chemical vapor deposition (PECVD) have inherent superiority due to their smooth surface, pin-hole free morphology, and dense crosslinked bulk structure. These spatially uniform films also exhibit good adhesion to a variety of substrates, excellent chemical inertness, high thermal resistance, and are formed from a rapid, inexpensive, solvent-free, room temperature process. In this work, we describe PECVD polymer dielectric films prepared from three precursors including benzene, octafluorocyclobutane (OFCB) and hexamethyldisiloxane (HMDS) using two different feed locations including in the plasma zone center and in the downstream region. The chemical structure of the PECVD films was determined by XPS, FTIR and ESR. The dielectric constant and dissipation of the films were studied over a range of frequencies up to 1 MHz, and the dielectric strength was characterized by the current-voltage method. Spectroscopic ellipsometry was performed to determine the thickness and refractive index of the resultant films.The PP-benzene films showed strong aromatic characteristics, PP-OFCB films maintained a high F/C ratio with a variety of fluorine moieties, and PP-HMDS retained a large fraction of Si-O bonds. All the PECVD films showed higher dielectric constants than those of corresponding conventional polymers. There is a small sharp drop in dielectric constant at low frequencies for all the PECVD films, attributed to the orientational polarization caused by trapped free radicals, oxygenated groups (C=O), and unsaturated moieties. The largest drop occurred for the PP-HMDS films. All films exhibit a continuous increase in dielectric loss as a function of frequency. Among all the PECVD films, the PP-benzene exhibited high breakdown strength. These variations in the dielectric properties are closely associated with the unique structure features of PECVD films.

We present the results of our investigation of new derivatives of cyclohexanone and piperidone compounds that have exhibited in the past anticancer effect due to biochemical destruction of cancer cells. In this study we focus on using these compounds as markers for malignant cells because of their strong two-photon excited fluorescence. Their molecular cross-section of two-photon absorption can be as high as 3000x10-50cm4s/photon and compares well with Rhodamine B, well-known fluorescent molecular probe. This provides an option for monitoring the biochemical destruction of cancer cells by means of two-photon excited fluorescence spectroscopy. Initially we studied the two-photon fluorescence of the solutions of pure compounds. Then we mixed the compounds with amino acids (Glycine and Alanine), the major building blocks of proteins in cells, hoping that the fluorescence will give some insight in the interaction between the compounds and bio substances. We discuss the solubility issues, the cross-section of twophoton absorption of the compounds, and also the features of the spectrum of the two-photon excited fluorescence. Compounds combining both properties (cytotoxicity and two-photon excited fluorescence), which are now carried by different chemical agents, are expected to improve the efficiency of cancer treatment and lower the cost.

A new synthetic method of octabromoporphyrin compounds has been created to simplify the conventional multi-step synthesis and purification to a one step reaction. A series of new meso-substituted β-bromoporphyrins, including tetraphenyloctabromoporphyrin (OBTPP), tetra-9-ethyl-carbazoleoctabromoporphyrin (TCarbOBP), tetra-2-thienyloctabromoporphyrin (T2-thioOBP), tetra-3-thienyloctabromoporphyrin (T3-thioOBP), tetra-5-bromo-2-thienyloctabromoporphyrin (5BrT2-thioOBP) and relative Zn porphyrins, have been prepared by this method. In this paper we discuss the synthesis of these compounds and their optical behaviors, especially the effects of the different meso-substituents on the photophysical properties. In order to investigate the different optical properties of porphyrins with β-bromo-substitution and without β-bromo-substitution, corresponding non-brominated meso-substituted porphyrins have also been synthesized and studied.

In this work, we describe the spectroscopic properties of a series of platinum complexes containing one acetylide ligand per platinum, having the chemical formula trans-Pt(PBu(3))(2)((C[triple bond]CC(6)H(4))(n)()-H)Cl, n = 1-3 (designated as half-PEn-Pt) and compare their spectroscopic behavior with the well-characterized series trans-Pt(PBu(3))(2)((C[triple bond]CC(6)H(4))(n)-H)(2), n = 1-3 (designated as PEn-Pt). This comparison aims to determine if the triplet state of PEn-Pt is confined to one ligand or delocalized across the central platinum atom. We measured ground-state absorption spectra, fluorescence spectra, phosphorescence spectra, and triplet-state absorption spectra. The ground-state absorption spectra and fluorescence spectra both showed a blue shift when comparing half-PEn-Pt with PEn-Pt, showing the S(1) state is delocalized across the platinum. In contrast, the phosphorescence spectra of the two types of compounds had the same 0-0 band energy, showing the T(1) state was confined to one ligand in PEn-Pt. The triplet state absorption spectra blue shifted when comparing half-PEn-Pt with PEn-Pt, showing the T(n) state was delocalized across the central platinum. This comparison supports recently published work that suggested this confinement effect (Rogers, J. E et al. J. Chem. Phys. 2005, 122, 214701).

A series of one-photon absorption spectra for fluorene-based donor-pi-acceptor molecules is presented and spectroscopically assigned, based upon the results obtained from time-dependent density functional theory. The computed excitation energies were generally shown to be in good agreement with experiment, particularly when compared to results from measurements carried out in a nonpolar solvent, which were available for some molecules. The computed oscillator strengths may resolve discordant experimental values in some cases, for example, for AF-380, AF-270, and AF-295. However, a quantitative comparison between computed and observed oscillator strengths is complicated by band overlapping. Thus, the computed extinction coefficients obtained by summing over the Gaussian bands are useful in such cases.

Utilization of two-photon (TP) excited fluorescence resonance energy transfer ( FRET) within a light-harvesting dendrimer has proven to be a reliable method for the enhancement of the effective TP absorption efficiency of many FRET acceptor molecules. This light-harvesting approach has enabled TP photosensitization of singlet oxygen from a porphyrin in both aqueous and organic media using wavelengths more transmissive to human body tissue (750-1000 nm). This ability to utilize near-infrared irradiation to induce photochemical reactions is especially attractive for applications including in vivo photochemistry, oxygen sensing, and photodynamic cancer therapy. In efforts to further the applicability of this concept, we synthesized an array of novel photosensitizers by metalation of the porphyrin core with aluminum, silver, and zinc. Time-resolved fluorescence, transient absorption measurements, and TP excitation experiments demonstrated efficient TP excited FRET to produce the porphyrin excited state triplet which subsequently generates singlet oxygen by the aluminum and zinc metalated species. Singlet oxygen photosensitization efficiency was found to be most efficient using aluminum followed by zinc and least efficient using silver. In fact, silver metalated photosensitizers were found to be nonfluorescent and incapable of generating a measurable amount of singlet oxygen. With the proper choice of inserted metals, it was possible to tune the efficiency of TP induced singlet oxygen production.

Sterically hindered fullerenyl chromophore dyad and triads, C-60(> DPAF-C-9)(x) (x = 1 and 2, respectively), in an acceptor-donor (A-D) molecular linkage of C-60-(keto-fluorene)(x) were synthesized and fully characterized. Attachment of two 3,5,5-trimethylhexyl groups on C-9 of the fluorene ring moiety greatly improves their solubility and makes direct intermolecular aromatic stacking contacts more difficult. They are the first series of fullerene derivatives showing high three-photon absorptivity (3PA). Accordingly, C-60(> DPAF-C-9)(2) exhibits 2PA and 3PA cross sections in the values of 0.824 x 10(-48) cm(4) s (or 82.4 GM) and 6.30 x 10(-25) cm(6)/GW(2), respectively, in femtosecond region among the highest ones reported for many diphenylaminofluorene-derived AFX chromophores. Utilization of a keto linker located immediately between C-60 cage and fluorene chromophore moieties facilitates molecular polarization of the DPAF ring toward the C-60 cage. That may serve as the fundamental cause for correlation of enhanced A-D electron interactions to, ultimately, observed multiphoton absorption cross sections. By using nanosecond laser flash photolysis results taken at 355 nm as the reference, transient absorption data obtained from femtosecond pump-probe experiments at 800 nm unambiguously verified the occurrence of two-photon excitation processes of C-60(> DPAF- C-9) in air-saturated benzene and subsequent efficient energy transfer from the two-photon pumped DPAF- C-9 moiety to the C-60 cage moiety.

A quinoidal porphyrin has been synthesised with such a curved pi-system that pi-pi stacking leads to the formation of cyclic trimer aggregates in the crystal, which pack to generate cylindrical channels with an internal diameter of 1.0 nm.

Extensive measurements and modeling of several two photon absorbing materials are described. These are used to elucidate the relative significance of various relaxation and excitation processes that come into play in nonlinear transmission (NLT) and two photon absorption cross section measurements. A reliable measurement of the one photon absorption cross sections at energies 0.5 to ~1.7 eV below the fundamental transition are presented with Voigt function fits that enable the determination of the Gaussian and Lorentzian line widths. Both a numerical model and an analytical model are developed neither of which use any adjustable parameters in comparing calculated NLT results to data. Both models fit the data relatively well over the full range of the experiment. The analytical model captures the primary causes of the nonlinear absorption in the low intensity regime and demonstrates that the nonlinear transmittance can be estimated as a simple effective three-photon process. The numerical model calculates the spatial and time dependence of three state populations and all of the transitions between these states. This model improves the quality of the nonlinear transmission fit which is due to the inclusion of the ground state absorption. Additionally an observation of a strong, long lived transient which is quenched by oxygen suggests multiphoton ionization is happening at low intensities. Thus the full range of constraints applicable to all measurements of the two photon cross section are presented.