Martin Danko

Spectral Properties of Substituted Coumarins in Solution and Polymer Matrices

The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH3, OCH3 and N(CH3)2, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH3)2 in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH3)2 substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5–4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have kF higher than knr in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.

Spectral characteristics and photochemical stability of fluorescence probes based on 1,8-naphthaleneimide in solution and in polymer matrix

Abstract Fluorescence probes of type N -(1′- R -2′,2′,6′,6′-tetramethyl-4′-piperidinyl)-1,8-naphthaleneimide exhibit spectral properties which are influenced by environment and substitution ( R ) on sterically hindered nitrogen of piperidine moiety. Absorption spectra of parent amine and its N substituted derivatives show the longest wavelength band around 340 nm (log ɛ ∼ 4.0) which is well resolved in cyclohexane. In polar methanol it is only slightly blue shifted. Substitution on sterically hindered nitrogen does not influence the absorption spectra in near UV region. Fluorescence spectra of the probes have maximum around 385 nm in methanol and comparable intensity as anthracene. In nonpolar cyclohexane the fluorescence intensity is low (more than 100×). In nonpolar isotactic polypropylene matrix the red shifted excimer like emission in the range 440–470 nm was observed. The N -oxy and N -hydroxy derivatives under the same conditions do not yield the excimer emission. In other polymer matrices as polystyrene, poly(methyl methacrylate) and polyvinylchloride similar emission as in methanol was observed, the emission in latter matrix being the most intense. The fluorescence lifetime in polar solvent and matrices is less then 1 ns and deviates slightly from monoexponential. In nonpolar iPP, the fluorescence lives longer around 5 ns and its decay is more complex. Intermolecular quenching of the probes by 1-oxy-2,2,6,6-tetramethyl-4-hydroxypiperidine in methanol occurs at the rate which is above the diffusion controlled limit what might indicate the involvement of the polar medium in the process. Intramolecular quenching, expressed as the ratio I NH / I NO for parent and oxidized amine respectively, strongly depends on the medium as well. In polar methanol this ratio is about 30 while in polymer matrices 2–4 only. Photolysis of probes doped in polymer matrices with radiation above 300 nm revealed that the parent amine is about 3× more stable as 1,8-naphthoic anhydride or N -octadecyl-1,8-naphthaleneimide.

Spectral Properties of Probes Containing Benzothioxanthene Chromophore Linked with Hindered Amine in Solution and in Polymer Matrices

Absorption and emission spectroscopy as well as laser flash photolysis was employed in order to characterize the spectral properties of novel probes based on benzothioxantheneimide chromophore covalently linked with different types of sterically hindered amines. These were chosen as 2-(2,2,6,6-tetramethyl-4-piperidyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTXINH), the equivalent stable nitroxyl radical, i.e. 2-(1-oxo-2,2,6,6-tetramethyl-4-piperidyl)thioxantheno[2,1,9dej]isoquinoline 1,3-dione (BTXINO) and the alkoxy derivative 2-(1-(1′-phenylethoxy)-2,2,6,6-tetramethyl-4-piperidyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTXINOR). Spectral properties, in solutions and in various polymer matrices such as polystyrene, polymethyl methacrylate, polyvinyl chloride and polypropylene, were compared with the compound 2-(1-dodecyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTXID) taken in the present study as a reference compound. By means of the fluorescence decay and in the contrary to three other probes, BTXINO probe clearly showed a biexponential decay while the three other probes led to monoexponential decay. Two different singlet excited states with lifetimes of about 0.4 and 5 ns were proposed. They correspond to two dispositions of the nitroxyl radical chain above and along the fluorescent moiety of the molecule. Such behaviour depends on the surrounding media. Moreover, an efficient intramolecular quenching of the fluorescence emission was only observed with the short lived singlet excited state. The ratio BTXID/BTXINO was found equal to about 4 and 9 in solutions and polymer matrices respectively. Laser flash photolysis indicated that the novel probes as well as the model compound yielded transient absorption with maximum at 530 nm, corresponding to the triplet states. The intermolecular quenching of such species by molecular oxygen and by free N-oxyl, such as 1-oxy-2,2,6,6-teramethylpiperidine (TEMPO) and 1-oxy-2,2,6,6-teramethyl-4-hydroxypiperidine (TEMPOL), and the intramolecular quenching was not efficient.

Preparation, photochemical stability and photostabilizing efficiency of adducts of 1,8-naphthaleneimide and hindered amine stabilizers in polymer matrices

Adducts of 1,8-naphthaleneimide and hindered amine stabilizer (HAS) such as 1-R-substituted-2,2,6,6-tetramethyl-4-aminopiperidine were prepared where R is –H, –O., –OH, –COCH3 and –OCOCH3. The photochemical stability of adducts was determined at photolysis in isotactic polypropylene, polystyrene and polyvinylchloride. Their photostabilizing efficiency was determined at photooxidation of isotactic polypropylene. The photochemical stability of the adducts is low in all matrices. The N-oxy derivative was the most stable in all matrices. The photolysis of all derivatives is the slowest in polystyrene. Intramolecularly combined chromophore/HAS are less effective stabilizers than in 1:1 mixture of separated components. The 1,8-naphthaleneimide chromophore decreases the stabilization efficiency of hindered amine structural units as compared to its absence.

Photochemical stability and photostabilizing efficiency of anthracene/hindered amine stabilizers in polymer matrices

Abstract Adducts of chromophore (anthracene substituted in position 9) and hindered amine stabilizers (HAS) such as 2,2,6,6-tetramethylpiperidine-4-yl 3-(9-anthracene)propanoate, 1-oxo-2,2,6,6-tetrametylpiperidine-4-yl 3-(9-anthracene)propanoate, [2,2,6,6-tetramethyl-piperidine-4-yl 3-(9-anthracene)propanoate]ium chloride as well as model compounds 3-(9-anthracene) propanoic acid and methyl 3-(9-anthracene)propanoate were investigated. The photochemical stability of the adducts was determined in photo-decomposition in polystyrene, poly(methyl methacrylate), poly(vinyl chloride), isotactic polypropylene (iPP) and low density polyethylene (LDPE). Their photo-stabilizing efficiency was determined in iPP and in LDPE. The rate of decomposition of adducts on irradiation λ> 310 nm was very fast in all matrices. Intramolecularly combined chromophore/HAS are more effective stabilizers than 1:1 mixtures of the separated components. The decomposition of anthracene produces free radicals containing HAS. These radicals are able to graft to the polymer chain of iPP and LDPE.

SPECTRAL CHARACTERISTICS OF FREE AND LINKED PYRENE-TYPE CHROMOPHORES IN SOLUTION, POLYMER MATRICES, AND INTERPENETRATING NETWORKS

Monomers, 1-pyrenylmethyl methacrylate (PyMMA), 1-pyrenylbutyl methacrylate (PyBMA), 4-(1-pyrenyl)methoxymethyl styrene (PyMMS) and allyl-(1-pyrenylmehtyl) ether (PyMAE), with pyrene as chromophore, were prepared. Their spectral properties (absorption, emission and emission decay) in solution, and doped or bonded in polymer matrices and complex polymer systems as interpenetrating polymer networks (IPN), were investigated. Spectral properties of pyrene-containing monomers doped in polystyrene (PS), polymethylmethacrylate (PMMA), polyvinylchloride (PVC), polyethylene (PE) and grafted on PE as well as copolymerized in buthylmethacrylate-co-styrene copolymer (BMA-co-S) have been compared. Absorption and emission spectra of pyrene type probes in solution and in IPN matrices exhibit typical absorption of the pyrene moiety. For IPN with grafted probes on PE, the absorption is slightly shifted to red wavelength. For monomers, PyMMA, PyBMA and PyMAE grafted to PE, the shape of the emission spectrum depends on the wavelength of excitation. The ratio of intensity of the vibrational band, I1/I3, (I1 peak at 377 nm and I3 peak at 388 nm) has been a quite useful indicator of polarity of IPN. The relative quantum yields of fluorescence in IPN matrices are lower in comparison to polymer matrices of PE, PS, PMMA for all probes under study. The fluorescence life-times for bound and free probes have been in the range 100–200 ns, which is substiantialy shorter than for the parent pyrene chromophore under the same or similar condition. Grafted probes on PE alone, or as a part of IPN, exhibit substantially shorter life-time around 10 ns and decay is rather complex.

Spectral characterisation of new organic fluorescent dyes with an alkoxysilane moiety and their utilisation for the labelling of layered silicates

New fluorescence dyes with an alkoxysilane moiety were synthesised by the condensation of 3-(triethoxysilyl)-1-propanamine (3-aminopropyltriethoxysilane) with 4,10-benzothioxanthene-3,1′-dicarboxylic acid anhydride (BTXA) and N,N-dimethylaminonaphthalene-1,8-dicarboxylic acid anhydride (DMANA), which was accompanied by the formation of an imidic bridge. The compounds N-(3-(triethoxysilyl)propyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTX-S) and 4-(N′, N′-dimethyl)-N-(triethoxysilyl)propyl-1,8-naphthalene dicarboxylic acid imide (DMAN-S) were characterised by steady-state and time-resolved fluorescence spectroscopy in chloroform and ethanol. Both conjugates (BTX-S and DMAN-S) exhibited absorption and emission bands in the same region as the un-substituted BTXA and DMANA. An important Stokes shift was observed for DMAN-S in ethanol. A high fluorescence quantum yield was observed for BTX-S in both solvents and for DMAN-S in chloroform. In addition, the newly developed fluorescent silane dyes were covalently attached to the microscopic particles of layered silicates and on the surface of SiO2 wafers as a proof of concept for fluorescence particle (surface) visualisation. The surface wafer modification was precisely characterised by X-ray photoelectron spectroscopy (XPS). Successful covalent linkage onto the particles of layered silicates was proved by confocal laser scanning microscopy technique.

3-(7-Dimethylamino)coumarin N-phenylsemicarbazones in solution and polymer matrices: Tuning their fluorescence via para-phenyl substitution

The photo-physical properties of five new para-phenyl substituted derivatives of 3-(7-dimethylamino)coumarin N-phenylsemicarbazone with various electron-withdrawing substituents R (RF, Br, CF3, CN or NO2) in the para-position on the phenyl ring were investigated in solvents and in polymer matrices. Tuning their fluorescent properties via para-substitution is discussed in terms of Twisted Intra-molecular Charge-Transfer (TICT) state formation, specific solute-solvent interactions (hydrogen bonding), fluorescent H-aggregates formation, and the solvent polarity and polymer matrix effects.

Biosensor for calcium based on a hydrogel optical waveguide with integrated sensor proteins

We present a new optical biosensor concept based on hydrogel waveguides with integrated fluorescent proteins developed as a platform for implantable sensors. In this prototype the sensor detects the presence or absence of calcium through changes in fluorescence resonance energy transfer (FRET) induced by conformational changes of a FRET protein. The protein is immobilized in a synthetic hydrogel matrix with cylindrical shape, which serves simultaneously as an optical waveguide for the excitation light. The specificity of the protein determines which molecule can be detected.

Characterization of interpenetrating polymer-like network based on polyethylene/poly(styrene-co-butylmethacrylate) (PE/P(S-co-BMA)) by non-radiative energy transfer

Preparation of labeled interpenetrating polymer-like network (IPN) composed of polyethylene and copolymer styrene and butylmethacrylate with polymerizable fluorescence probes based on phenanthrene and anthracene was described. This pair of fluorescence probes, namely (phenathrene-9-yl)methyl methacrylate and (anthracene-9-yl)methyl methacrylate, was used to explore the non-radiative energy transfer in this special polymer blend. It was demonstrated that the energy transfer between phenanthrene moiety attached to copolymer part of IPN and anthracene moiety attached to PE part of IPN occurred in rather limited extent due to micro-heterogeneous structure of this polymer blend. Fluorescence experiments with dyes attached solely to the copolymer S-BMA part of IPN indicated that these dyes were concentrated in this part of IPN.