In this work we present our new experimental and theoretical results upon investigations of the photoinduced
tautomerism processes of single metal-free porphyrin-type molecules. During tautomerization a molecule changes its
structure, therefore the excitation transition dipole moment (TDM) of the molecule changes its orientation. Using
confocal microscopy in combination with azimuthally and radially polarized laser beams we are able to determine the
orientation of the TDM as well as the orientation of a single molecule itself. In the case of tautomerism we are able to
visualize this process and even the involved isomers separately. The study first focuses on two symmetrical compounds:
a phthalocyanine and a porphyrin. Additionally, differences of the single molecules embedded in a polymer matrix or
just spin-coated on a glass cover slide and under nitrogen flow are investigated. In the latter case we observe a higher
frequency of the change of the TDM orientation. The experimental studies are supplemented by quantum chemical
calculations. Variations of the molecular substituents, the environment and excitation wavelength can give new insights
into the excited-state tautomerism process of a single molecule. We also introduce some suggestions for future experiments to support the understanding of the photoinduced tautomerism.
The series of (tert-butyl)catechol-substituted fluorinated naphthalocyanines 1, 2 and 3 displays limiting of the optical power generated with nanosecond light pulses simultaneously at 532 and 1064 nm. Limiting thresholds of 1-3 fall in the range 1.5-2.7 J cm-2 at 532 nm and 2.6-3.7 J cm-2 at 1064 nm when linear transmittance is 0.75 at both wavelengths of analysis. Compared to other unsubstituted naphthalocyanines, 1-3 show a relatively large window of high linear optical transmission between the characteristic Q- and B- absorption bands (above 0.75 for a 250 nm-wide window when 1-3 concentration is in the order of few millimoles per liter in 1 cm thick cells). A general enhancement of photostability in 1-3 is observed for the presence of electron-withdrawing fluorine substituents. The optical limiting effect produced by these systems is evaluated for the protection of optical sensors which operate in both visible and NIR spectral ranges, e.g. the human eye and night vision devices.
The use of lasers as the driving force of information processing for future photonic technologies is almost inevitable. As a direct consequence of this the protecting of targets from high intensity stray optical beams, the most important being the eye, via optical limiting (high suppression of high intensity optical beams whilst allowing high transmission of ambient light) is a task of immediate importance. This contribution will discuss the application of metallo-phthalocyanine compounds doped into organic polymers to produce composite films to act as passive solid-state optical limiters. A range of phthalocyanines with different metals such as zinc, indium and vanadium substituted into the central cavity doped into the comercially available polymer poly(methyl)-methacrylate, PMMA, is investigated. The nonlinear responses exhibited by the systems are modelled and fitted using a three level orbital model to quantify the nonlinear activity in an effort to elucidate certain molecular design rules for the optical limiting application of the solid-state polymer-phthalocyanine composite. In addition to this the nature and physical properties of the films that are processed are also discussed.
Experimental measurements of optical limiting resulting from reverse saturable absorption in metallo-phthalocyanine and metallo-naphthalocyanine compounds are reported. Open aperture ns z-scan with Gaussian pulses are employed to investigate the interaction of high intensity light with the novel compounds. Rate equations are used to analytically solve the static state solution that simulates the excited state dynamics resulting from the nonlinear excited state absorption, and this is fitted to the experimental data. General molecular engineering trends relating the optical limiting performance of these compounds to their structural characteristics are explored and discussed.
We discuss the photovoltaic and electroluminescence properties of three groups of optoelectronic devices with the following organic materials: (A) single layer devices made of para-hexaphenyl (PHP), pristine methyl-substituted laddertype poly-para-phenylene (mLPPP) and N-(2,6- Diisopropylphenyl)-N'-octylterrylene-3,4,11,12-tetracarboxdiimide- (DOTer) sandwiched between ITO and Al electrodes, (B) mLPPP blended with TiO-phthalocyanine (TiO-Pc) and an aromatic macromolecule, (C) multilayer devices consisting of differently arranged layers made of mLPPP, PHP and DOTer. The motivation for these experiments is the optimization of either charge transfer or energy transfer from one molecular to its neighbor molecule. In order to obtain high photocurrents for photovoltaic applications it is favorable to use a combination of a polymer with electron donor properties and an organic substance with high electron affinity, which provides efficient charge transfer resolution in the creation of polarons. In particular we investigated the influence of the location of the photoactive region on the shape and magnitude of the photocurrent action spectra by performing experiments under electrical and optical bias for different excitation conditions. The best photovoltaic yields were obtained for hetero-structure devices.
Oligo-phenylenevinylenes (OPV) with a series of distance controlling, electron donating, and/or electron withdrawing substituents are deposited from vapor phase and solution as ultrathin films or nanoparticles with diameters of 20 - 200 nm. In some cases the systems are doped at levels of 10-5 - 10-3 with energy accepting OPV's of longer chainlengths. Absorption and fluorescence spectra, steady-state and time-resolved anisotropies, radiative and nonradiative deactivation rates of these systems are investigated and compared to the corresponding properties in dilute solutions. Fluorescence yields of the parent oligomers and their alkyl or oxyalkyl derivatives are high in solution with an `infinite' chain limit of (Phi) F approximately equals 0.5 and an upper radiative rate constant limit of kr(infinity ) equals (1 +/- 0.3) (DOT) 109 s-1. Yields and kr decrease strongly in films and nanoparticles because of H-aggregate formation. However, doping with fluorescent acceptors can increase the yields up to (Phi) F yields 0.7. Introduction of electron withdrawing -CN and -SO2CF3 substituents reduces (Phi) F in low viscous dilute solutions almost to zero. High viscosities and condensation to solid phases will rise the yields up to (Phi) F yields 0.6 because of suppression of nonradiative torsional deactivation and formation of J- aggregates with high kr.
Soluble titaniumoxophthalocyanines RmPcTiO with m = 4,8 and R = n-alkyl (C3-C7), trifluoromethyl, trifluoroethoxy, and the corresponding (t-butyl)4-naphthalocyanine are synthesized. The compounds are characterized spectroscopically, photochemically, and photoelectrically in solution and in vapor deposited or spin cast films. The results are compared to the insoluble parent compound PcTiO. According to positions of the electronic absorption bands, the films form amorphous and several crystalline phases depending on deposition and annealing conditions. All compounds are very weak electrical conductors in the dark, but much better ones upon irradiation. Conductivity increases also extremely upon oxygen doping. This effect is kinetically investigated and assigned to light assisted formation and dissociation of stable chemical complexes between Pc and 02. Complex formation is reversible to a high degree, but also irreversibly oxidized photoproducts are formed. Photoconductivity increases as function of chemical substituents in the series alkyl < BuNcTiO < PcTiO. The same series is also valid for stability against photooxidation in solution (as far as soluble) and in the films. For unannealed films of BuNcTiO and PcTiO the quantum yields for photooxidation in ambient atmosphere are in the order of φph = 10-6. After annealing, the yields of decomposition decrease by additional 1 -2 orders of magnitude.
Non specific localization of photosensitizers after application in vivo limits progress in PDT. Relatively selective distribution of photosensitizers in malignant tissues is crucial for a successful treatment. The target specificity of photosensitizers may be improved by linking photosensitizers with monoclonal antibodies. In this approach, a high specific monoclonal antibody, BM-2 which is directed against epitopes of the mucine glycoprotein TAG-12 was used. This antibody shows reactivity with 96% of all primary breast carcinomas. BM-2 was conjugated with a second generation phthalocyanine photosensitizer which is only weakly phototoxic to human T-47D tumor cells without conjugation in vitro. With respect to future clinical application, illumination times from 25 to 100 minutes and a powerful diode laser with an emission of 690 nm was chosen, which provides deeper tissue penetration in vivo. We observed phototoxicity towards T-47D human breast carcinoma cells at concentrations ranging from 0.25 to 6 micromol/L and light doses from 6 to 24 J/cm2. The immunoconjugates discriminated mucine-positive and mucine-negative tumor cells and showed high photocytotoxic selectivity towards mucine-positive T-47D cells in vitro. The conjugate showed no dark toxicity. In vivo experiments will follow.
Results of experiments on photoconductivity of one-dimensional bridged polymeric phthalocyanines [PcML]n consisting of different combinations of macrocycles, Pc, bridging ligands, L, and central metal atoms, M, are described. It is shown that the spectral response and photoconductive gain strongly depend on the type of bridging the planar phthalocyanine rings. Therefore, rules for the development of phthalocyanine-based polymeric photoconductors by synthesis, e.g., with significant long wavelength sensitivity, can be outlined.