A series of 2,7-disubstituted organogold(I) fluorenyls has been synthesized with full ground-state and optical characterization. Gold(I) is attached to the fluorenyl carbocycle through direct C–Au σ-bonds, or through intervening alkynyl linkages. The new complexes are dual fluorescence and phosphorescence emitters, leading in some cases, to apparent white light emission. Excited-state dynamics have been measured by ns and ultrafast transient absorption spectroscopy, and rate constants for radiative and nonradiative decay, and intersystem crossing, have been obtained. Both fluorescence and phosphorescence originate from metal-perturbed ligand-centric charge-transfer excited states. Compositions of the relevant frontier orbitals were calculated from density-functional theory.
The effects of incorporation into a solid matrix on the photophysical properties of a nonlinear material have been of interest for some time in our group. It is well known in the literature that for a nonlinear absorbing dye to be the most effective, high concentrations are generally needed. Understanding how the larger concentration and placement into a solid matrix affects their photophysical properties is the key of this study. Here we look at two metallated substituted tetrakis(cumylphenoxy) phthalocyanines with either Pb or In as the central metal. A detailed study of their photophysical properties based on concentration allows for a better understanding of the constraints this environment has to a given material.
It is well known in the literature that for a two photon nonlinear absorbing dye to be the most effective, high concentrations are needed. The problem is that most photophysical studies in solution are done at low concentration and in a solution. These low concentration studies are important for understanding inherent materials properties but it is also important to understand what happens in a material at high concentration. In addition to this, efforts have been made to study the effects of incorporating a dye into a solid matrix environment to better understand the constraints this environment has to a given material. Preliminary results for an epoxy system reveal the formation of excimers (excited state dimers) with an increase in concentration. Excimers are forming from the triplet excited state of the E1-BTF. A rate constant for this formation is 2.6 × 105 M-1 s-1. While rather slow, at greater than 50 mM concentration the excimer is readily formed with <90% efficiency. This must be considered when making nonlinear absorption measurements since the excimer will certainly contribute to the overall nonlinearity.
In order to understand electronic and conformational effects on structure-spectroscopic property relationships in platinum acetylides, we synthesized a model series of chromophores trans-Pt(PBu3)2(CCPhenyl-X)2, where X = NH2, OCH3, diphenylamino, t-Bu, methyl, H, F, benzothiazole, trifluoromethyl, CN and nitro. We collected linear spectra, including ground state absorption, phosphorescence and phosphorescence excitation spectra. We also performed DFT and TDDFT calculations on the ground and excited state properties of these compounds. The calculations and experimental data show the excited state properties are a function of the electronic properties of the substituents and the molecular conformation.
A pseudo-symmetric two-photon absorbing dye (1) containing a central piperazine unit substituted with (benzothiazol-2- yl)-9,9-diethylfluoren-2-yl pendant groups has been synthesized and characterized. The molecule has a two-photonabsorption cross-section of σ2 = 140 GM in tetrahydrofuran at ~ 740 nm and shows significant solvatochromism in the excited-state fluorescence spectra. The emission spectra broaden and the maxima bathochromically shift from 411 nm to 524 nm in n-hexane and acetonitrile, respectively. Moreover, the central piperazine moiety serves as a potential chelation site for ions. Addition of copper(I) hexafluorophosphate and zinc(II) triflate in acetonitrile indicate ground-state complexation with a shift in the emission maximum from 524 nm to 489 nm and 487 nm, respectively. Interestingly, the newly formed Cu and Zn complexes are more strongly emissive than the free dye. Finally, addition of p-toluenesulfonic acid in tetrahydrofuran also blue-shifts the emission maximum, but the intensity is quenched. Due to the photophysical changes induced by addition of metal ions and protons, the dye shows promise as a potential sensor.
Experimental measurements were performed to completely characterize the linear and nonlinear optical properties in butyl salicylate solution of a novel bipyridyl platinum(II) complex bearing benzothiazolylethynylfluorene ligands. This paper describes the analysis of the resulting experimental data and reports the values of the ground- and excited-state absorption cross sections and of the other photophysical parameters characterizing the chromophore/solvent system.
The binding of DNA-CTMA (Deoxyribonucleic acid-cetyltrimethylammonium) complex with two tetrameric Copper Phthalocyanine (CuPc) systems, substituted with carboxylic acid (CuPc-COOH) and derivatized further as an imidazolium salt (CuPc-COOR), was investigated in dimethylsulfoxide (DMSO) solutions using UV/Visible Spectroscopy. Absorbance changes at 685 nm (Q band of the CuPc) were monitored as a function of DNA-CTMA added to the dye solution and stock concentrations of DNA-CTMA in DMSO were varied to facilitate observation of the full binding process. Our findings indicated that while binding with DNA-CTMA was more well-defined in the case of CuPc-COOH, the binding profile of the CuPc-COOR showed initial growth followed by decay in its Q-band absorbance which was indicative of a more complex binding mechanism involving the dye and DNA-CTMA. Preliminary findings from photophysical studies involving the CuPc tetramers and DNA-CTMA are also discussed in this paper.
We have been studying exciplex formation in nonlinear optical materials containing a high concentration of 2PA chromophores (AFX dyes) as a means to enhance the nonlinear optical properties. A number of dipolar AFX dyes having various electron-accepting moieties (π-excess and π-deficient examples) and three bisimide compounds having substituents with varying electron-withdrawing power were synthesized to study exciplex formation in their solid state blends. In substrate supported thin films of various equimolar blends containing an AFX dye and bisimide, the dye monomer emission was severely quenched, and a new emission, red-shifted by up to 110 nm, appeared. The emission energies were consistent with the charge recombination energy calculated from the energy levels of the donor and acceptor present in the blend, which confirmed the emission was from an exciplex. Time resolved emission measurements also indicated the presence of much longer lived transients in the blends, consistent with exciplex formation. Spectroelectrochemistry confirmed that the radical cations of these dyes had strong absorption in the NIR region, so exciplex formation is a means to enhance nonlinear optical absorption of the dyes in this spectral region.
To develop a structure-spectroscopic property relationship in platinum acetylides having poly(aromatic hydrocarbon)
ligands, we synthesized a series of chromophores with systematic variation in the number of fused aromatic rings(nFAR)
and ligand topology(polyacene(L), polyphenanthrene(Z) or compact(C)). We measured ground state absorption,
fluorescence and phosphorescence spectra. We also performed nanosecond and picosecond flash photolysis
experiments. To extend the range of compounds in the structure-property relationship, we did DFT calculations on an
expanded series of chromophores to calculate the S1 and T1 state energies. In both the DFT results and experiment, the
ground state and phosphorescence spectra are a function of both nFAR and ligand topology. In the L chromophores, the
S1 and T1 state energies decrease linearly with nFAR. In contrast the S1 and T1 state energies of the Z chromophores
oscillate with increasing nFAR. The C chromophores have behavior intermediate between the L and Z chromophores.
The picosecond transient spectra show complex behavior, having spectra reflecting intersystem crossing, vibrational
cooling and solvent relaxation processes. The nanosecond transient spectra result from the T1 - Tn transition. The timeresolved
spectra show no systematic variation with structure, showing more complex behavior than previously studied
platinum acetylides having phenylene ethynylene ligands.
There has been much interest in the development of two-photon absorbing materials and many efforts to understand the
nonlinear absorption properties of these dyes. We have recently explored a new type of two photon absorbing dye
containing a platinum center with ligands that vary in length that contain electron withdrawing benzothiazole. With
increased π-π* conjugation we expect to observe a red shift in the absorption properties of the material. We have
investigated the photophysical properties of the platinum chromophores using a variety of experimental techniques.
Previously we determined that the singlet and triplet excited states are responsible for nearly all of the nonlinearity in the
nanosecond regime accept the two photon mechanism that is primarily used for excitation. Therefore we would like to
tune the photophysical properties of both the singlet and triplet excited state in these materials. To our surprise we found
there is quite a bit of red shifting due to a metal-to-ligand charge transfer from the platinum to the ligand rather than the
expected shifting due to increased π-π* conjugation. However, with increased ligand length the chromophore does take
on more π-π* character.
There has been much interest in the development of two-photon absorbing materials and many efforts to understand the
nonlinear absorption properties of these dyes but this area is still not well understood. A computational model has been
developed in our lab to understand the nanosecond nonlinear absorption properties that incorporate all of the measured
one-photon photophysical parameters of a class of materials called AFX. We have investigated the nonlinear and
photophysical properties of the AFX chromophores including the two-photon absorption cross-section, the excited state
cross-section, the intersystem crossing quantum yield, and the singlet and triplet excited state lifetimes using a variety of
experimental techniques that include UV-visible, fluorescence and phosphorescence spectroscopy, time correlated single
photon counting, ultrafast transient absorption, and nanosecond laser flash photolysis. The model accurately predicts the
nanosecond nonlinear transmittance data using experimentally measured parameters. Much of the strong nonlinear
absorption has been shown to be due to excited state absorption from both the singlet and triplet excited states. Based on
this understanding of the nonlinear absorption and the importance of singlet and triplet excited states we have begun to
develop new two-photon absorbing molecules within the AFX class as well as linked to other classes of nonlinear
absorbing molecules. This opens up the possibilities of new materials with unique and interesting properties.
Specifically we have been working on a new class of two-photon absorbing molecules linked to platinum poly-ynes. In
the platinum poly-yne chromophores the photophysics are more complicated and we have just started to understand what
drives both the linear and non-linear photophysical properties.
Large two-photon and excited state absorption have been reported in donor-acceptor-substituted π-conjugated molecules.
We have performed detailed nonlinear absorption and photophysical measurements on a system of AFX chromophores
and calculate the nonlinear transmission based on an effective three-level model. A numerical model that includes
far wing linear absorption has been developed and compared with an analytical three-photon absorption model.
The models are in accordance and yield excellent agreement with experimental nonlinear transmission data for 0.02-M
AFX solutions up to laser intensities ~ 1-5 GW/cm2. We have extended our modeling efforts to include some new effects
that may be anticipated in this regime, such as stimulated scattering, molecular interactions, and saturation. Effects
of chirped pulses and linewidth of the pump laser on stimulated scattering are included. Self-focusing and de-focusing
are also considered. We report on our experimental observations of various materials and discuss results with respect to
our extended theoretical models.
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.
We report photophysical measurements and application of an effective three-photon absorption model that characterize the two-photon and excited state absorption in organic D-π-A chromophores. The key parameter is an effective three-photon absorption coefficient that depends on the intrinsic molecular two-photon absorption cross section and excited state photophysical properties. We measure all of these molecular parameters independently in a variety of experiments and then compare the model predictions with nanosecond nonlinear absorption measurements. We find excellent agreement with the data using only experimentally measured molecular quantities and no free parameters. We conclude that excited state absorption from both singlet and triplets states is the dominant contribution to the nonlinear transmittance loss in the nanosecond regime, and that the chief role of two-photon absorption in this regime is to populate the excited triplet state.
To develop novel nonlinear dyes for photonic applications, we synthesized a series of transition metal-containing phenylacetylene oligomers. Theoretical properties of these compounds were measured by UV/Vis absorption, photoluminescence, and nanosecond flash photolysis experiments. It was found that as the number of oligomer units increased ,the transition energies decreased without saturation. The low ground state absorption and UV absorption edge gives rise to solutions that are nearly water clear. A very broad triplet state absorption extending from the absorption edge to the limits of our spectrometer is demonstrated to also be intense. These results enhance the understanding of these materials when used for nonlinear absorption applications and enable the prediction properties for materials extending this class of dyes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.