Proc. SPIE. 6733, International Conference on Lasers, Applications, and Technologies 2007: Environmental Monitoring and Ecological Applications; Optical Sensors in Biological, Chemical, and Engineering Technologies; and Femtosecond Laser Pulse Filamentation
In this paper we report on the possibility to design the luminescent molecular thermometer for the cryogenic
temperatures. The approach is based on the high temperature sensitivity of the Pd-porphin phosphorescence in <i>n-</i>alkane
matrices. The dependence of radiative deactivation of Pd-porphin triplet states on temperature has been studied in
Shpol'skii matrices in the temperature interval of 1.2-210Κ . The dramatic changes in the phosphorescence spectra were
observed upon temperature rise, which were due to inclusion of the thermally activated states of Pd-porphin in the
processes of radiative deactivation. At liquid helium temperature <i>T</i><sub>1</sub>→<i>S</i><sub>0</sub> emission is observed only, and an increase in
temperature leads to the activation of <i>T</i><sub>i</sub>→<i>S</i><sub>0</sub> radiative transitions, so new additional bands appear. Activation energy <i>E</i><sub>a</sub>
of these states has been measured in <i>n-</i>octane and <i>n-</i>nonane matrices. The splitting value of the lowest quasidegenerate
triplet state Δ<i>E</i>(<i>T</i><sub>2</sub>-<i>T</i><sub>1</sub>) has been determined for both planar and distorted conformations of Pd-porphin macrocycle in noctane
matrix, amounting to 40 and 57 cm<sup>-1</sup>, respectively. The workability of dependence of Pd-porphin phosphorescent
properties on temperature in the design of the molecular thermometers for the temperature range from few K up to temperatures close to the melting point of <i>n</i>-alkane matrix (150-200 K) was shown.
In this paper we report the spectral manifestation of existence two spectral forms of Pd-porphin in wide set of Shpol'skii
matrices at cryogenic temperatures. The short-wavelength spectral form is attributed to the structure, where the central
Pd(II) ion is in plane of the porphyrin macrocycle, while the long-wavelength form is associated with the nonplanar
saddle-type conformation of the PdP. The frequencies of the normal vibrations in the ground electronic state have been
measured separately for both forms and the differences in the normal modes of two macrocycle conformations are
discussed. The type of molecule distortion has been established with using information about the frequencies of vibronic
modes from high-resolved spectra of metalloporphins. Matrix effect was shown to have significant role in the stabilization of each of two conformations.
In this paper we report the spectral manifestation of different spectral forms obtained for Mg-, Zn-, Pd- and Pt-porphins
in solid matrices (Shpol'skii matrices, solid tetrahydrofuran and rare gas matrices) at cryogenic temperatures. The planar
and two kinds of distorted conformations of Mg-, Zn-porphins in highly-resolved fluorescence spectra have been
detected. For Zn-porphin distorted forms have been detected in the fluorescence and phosphorescence spectra
simultaneously. In the phosphorescence spectra of the Pd- and Pt-porphins the manifestation of the two forms in the
ground state has been proved also. Energy splitting in the phosphorescence spectrum of the Pd-porphin in <i>n-</i>octane at 4,2
K comes to 78 cm<sup>-1</sup> for two forms of the Pd-porphin. Under selective excitation in S<sub>0</sub>-S<sub>1</sub> channel the large set of sharp lines was detected for each of two forms and vibrational frequencies have been determined. In highly-resolved
phosphorescence spectra of Pt-porphin in <i>n-</i>octane at 4,2 K we have detected similar manifestation of the two spectral
forms in the phosphorescence spectrum. To estimate the type of molecule distortion the information about the
frequencies of vibronic modes from well-resolved spectra of metalloporphins have been used.
In this paper we report on the study of S<sub>2</sub>→S<sub>0</sub> blue fluorescence and two-photon absorption (TPA) for a series of Zn-tetrabenzoporphyrins
(Zn-TBP) with sequential substitution of phenyl groups in <i>meso</i>-positions. The blue fluorescence
has been measured with both one- and two-photon excitation. The data on TPA showed that lowest <i>g-</i>parity state lies
above B-state for all these compounds and blue fluorescence has been detected upon two-photon excita<i>g</i>tion at <i>g</i>→<i>g</i>
transition energies above that of Soret band. The data are in line with the suggested role of the g-parity low-lying state in
the nonradiative deactivation of B state. More than two-fold decrease in the relative yield of blue fluorescence was found
in going from Zn-monophenyl-TBP to Zn-tetraphenyl-TBP. The enhancement of the radiationless internal S<sub>2</sub>→S<sub>1</sub> and
S<sub>1</sub>→S<sub>0</sub> conversion and the decrease in the quantum yield of blue fluorescence was proposed to explain by nonplanar distortions of tetrapyrrolic macrocycle in Zn-tetraphenyl-TBP. The obtained results indicate that the positioning of <i>g-</i>parity excited states above B states is a requirement but not the sufficient condition for presence of blue fluorescence.
Porphyrins and related molecules with strong two-photon absorption (TPA) are extremely called for because of several emerging applications, including 3D optical memory, high-resolution fluorescence microscopy and photodynamic therapy. In this paper we demonstrate for the first time that an asymmetric <i>meso</i>-substitution of porphyrin macrocycle with electron-donating diphenylamino-stilbene or bis-(diphenylamino)-stilbene groups results in a drastic enhancement of intrinsic TPA cross section in the near-IR region. The cross section value amounts to 500 - 900 GM depending on substituent group and link structure, which is about 10<sup>2</sup> times the corresponding value for the unsubstituted parent molecule. Compared to symmetrical porphyrins, the TPA spectra of this series follow qualitatively the corresponding one-photon spectra. Therefore, we describe the observed TPA spectra and absolute cross section values by taking into account the change of permanent dipole moment upon excitation. A new zeroth-generation dendrimer, consisting of a porphyrin core, symmetrically <i>tertakis-meso</i>-substituted with strong TPA dendrons, reveals 7 times increase of the cross section (740 vs 110 GM) as compared to its <i>mono-meso</i>-substituted analogue. We also demonstrated an efficient singlet oxygen generation upon two-photon excitation of these new molecules, which makes them particularly attractive for photodynamic therapy.
At present a special attention is concentrated on increasing of the efficiency of multi-photon absorption of organic systems because of new emerging applications based on this effect. In our experiments we use strong two-photon absorbing chromophore, 4,4’-bis(diphenylamino)stilbene (BDPAS), to design new dendrimer molecules, in such a way that the branching center allows for pi-electronic conjugation between branches. Here we present, for the first time, unambiguous spectroscopic evidence of strong cooperative enhancement of two-photon and three-photon absorption in a series of these dendritic macromolecules. Maximum two-photon cross section increases in proportion to N<sup>2</sup>, where N = 2, 4, 6 is the number of constituent identical chromophore units in the parent BDPAS and lowest, G-0 dendrimer generation. Almost the same scaling law is observed for three-photon absorption. For higher generations, G-1 and G-2, comprising N = 14 and 30 chromophores, respectively, the cooperativity in multiphoton response starts to saturate. We show that three-photon absorption provides important complementary information, which we use for evaluation of the size of domains where chromophores are coherently coupled.
We study absolute cross section of simultaneous two-photon absorption (TPA) in a series of porphyrins and tetraazaporphyrins by 100-fs-duration pulses in two ranges of laser wavelength, from 1100 to 1500 nm and from 700 to 800 nm. The cross section in Q transition region is, sigma(2) ~ 1-10 GM, and is explained by partial lifting of the parity prohibition rule. In Soret transition region we find enhancement by about an order of magnitude due to Q transition, which acts as a near-resonance intermediate state, and also due to gerade energy levels, which we identify in this spectral region. Further enhancement (up to sigma(2) ~ 1600 GM) is achieved by symmetrical substitution in tetraazaporphyrins with strong electron acceptor groups.
Classical photodynamic therapy (PDT) has a drawback of limited penetration of visible light. It has been proposed that by utilizing two-photon absorption (TPA), where illumination is carried out at near-IR wavelengths falling into tissue transparency window, the PDT can be used for deeper treatment of tumors. Here we introduce new porphyrin photosensitizer 5-(4-diphenylaminostilbene),15-(2,6-dichlorophenyl)-21H,23H- porphine (hereafter referred as DPASP) with greatly enhanced TPA cross-section in near-IR range of wavelengths. The design of DPASP was based on structure-property relationships, empirically known to enhance TPA cross-section in organic (pi) -conjugated chromophores. In our case introduction of a 4-(diphenylaminostilbene)-substituent into the 5-position of the tetrapyrrole ring results in 20-fold enhancement of TPA cross-section at (lambda) <SUB>exc</SUB> = 780 nm as compared with parent molecule 5-phenyl,15-(2,6-dichlorophenyl)-21H,23H-porphine (DPP). The high value of TPA cross-section of DPASP enables to reliably detect for the first time an efficient luminescence of singlet oxygen produced upon two-photon excitation of porphyrin. Singlet oxygen luminescence was also measured upon two-photon excitation of several other porphyrins including water-soluble derivative 5,10,15,20-tetrakis-(4-N-methylpyridyl)-21H,23H-porphine (TmpyP).
The process of the oxygen photodissociation and rebinding with human hemoglobin have been studied by the time-resolved absorption spectroscopy. The primary quantum yield (gamma) <SUB>o</SUB> does not depend on the pH and its estimated value is 0.3 +/- 0.1. The apparent quantum yield (gamma) corresponding to the portion of O<SUB>2</SUB> molecules which escape from the protein to the solvent depends on the pH. It has been shown that the entrance and exit of the oxygen molecules into/from the globin matrix is controlled by the same Bohr residues. The pK values were calculated and the attribution was made. The unusual behavior of the oxygenation parameters at pH > 8.5 was observed and explained by the action of the (alpha) 140-Tyr and (beta) 145-Tyr. The picosecond ligand rebinding dynamics were measured and the phenomenon of the pK value change was studied. It was explained by the subunit tertiary structure relaxation in terms of the transition between deoxy-R- and oxy-R- structures of the tetramer protein.