Reactive Phenanthrene Derivatives as Markers of Amino Groups in Fluorescence Microscopy of Surface Modified Micro-Zeolite L.

Two reactive phenanthrene derivatives, 4-(1H phenanthrol [9,10-d] imidazole-2-yl) benzaldehyde (PIB) and 6,9-dimethoxyphenanthro[9,10-c]furan-1,3-dione (PA) with high fluorescent quantum yields were prepared and used as fluorescent marker in fluorescence microscopy. In particular, silane modified µmZeolite-L containing amino group (-NH2) in the surface were labeled with the phenanthrene derivatives allowing good imaging resolution and spectroscopy measurements. The presence of a large Stokes shift of the probes due to their intramolecular charge-transfer character gives an advantage of the compounds in confocal laser fluorescence microscopy due to easy signal separation in excitation and emission wavelengths. On the other hand, these results open up the possibility of using these probes for visualization of Zeolite-based materials commonly used as catalysts in thermal and photochemical reactions.

Fluorescence from bisaryl-substituted maleimide derivatives.

A series of bisaryl-substituted fluorescent maleimides was synthesized via the Heck arylation. The compounds showed broad fluorescence emission bands in the visible region, a large Stokes shift in polar solvents and emission quantum yields varying from 0.04 to 0.71, depending on the structure and solvent medium. The difference in dipole moments of ground and excited electronic states of about 12 Debye is ascribed to a substantial charge shift and push-pull character of bisaryl-substituted maleimides. The fluorescence decays of N-benzyl-3,4-bis(4-methoxyphenyl)-1H-pyrrole-2,5-dione (compound 5a) are biexponential with short (1.3-7.6 ns) and long lived (11.5-13.6 ns) components in polar solvents, but in 1,4-dioxane and THF the decays become single exponential. On the other hand, N-benzyl-3-(4-methoxyphenyl)-4-(4-hydroxyphenyl)-1H-pyrrole-2,5-dione (compound 5b) exhibited a biexponential decay in DMSO and in DMF with much shorter decay components, and such behavior indicated a charge shift process combined with solvent assisted proton transfer in the excited state.

Photoinduced intramolecular charge transfer in 9-aminoacridinium derivatives assisted by intramolecular H-bond.

Fluorochromic dyes derived from 9-aminoacridinium containing a vinylene function with electron withdrawing groups such as diethyl [(acridinium-9-ylamino)methylene]malonate (I), ethyl [(acridinium-9-ylamino)methylene]cyanoacetate (II), [(acridinium-9-ylamino)methylene]malononitrile (III), are prepared and studied in their monoprotonated form. Absorption spectra of the new dyes are red shifted compared to that of the precursor dye. The observed dual fluorescence and multiexponential decay are ascribed to normal emission from the acridinium chromophore in addition to excited-state intramolecular charge transfer (ESICT) process. However, biexponential decay character is observed only for the dicyano derivative (compound III), whereas for the two other systems, more complex kinetics and a three-component decay is recovered. The analysis of the fluorescence decays in different solvents for the first two compounds reveals two short-lived components in the range of 160-350 ps and 1.1-3.0 ns, related to formation and decay of the ESICT state, plus a third one with decay time of about 9 ns, which is ascribed to the normal emission from the acridinium chromophore as an enol tautomer or as an intramolecular H-bond conformer (closed form tautomer). For the dicyano derivative, in which the absence of carbonyl group precludes the H-bond interaction, the biexponential fitting reveals a slightly fast formation rate of the ESICT state with values on the order of 10(10) s(-1), whereas its decay time is between 0.6 and 3.2 ns, depending on the solvent used.

Spectroscopy of auramine fluorescent probes free and bound to poly(methacrylic acid).

Auramines containing a vinyl group with strong electron-withdrawing substituent exhibit a pi-conjugated extended effect that gives a red shift in their absorption and emission bands. The new fluorochromic dyes were bound to poly(methacrylic acid) (PMA), and their photophysical dynamics in methanol and in aqueous solution were studied. These derivatives were also used as optical probes for copolymerization process. The process was monitored by the changes in electronic absorption with a concomitant fading of the free vinyl auramine absorption band in the red and an appearance of a UV band ascribed to dye bound to the polymer chain. The conformational transition of PMA with solvent and pH was clearly observed by the drastic changes in the photophysical properties of these auramine derivatives attached to the polymer chain. Time-resolved experiments revealed an unusual long-lived decay component of about 2.2-2.6 ns in aqueous solution at low pH together with two picosecond components (50 and 570 ps). Such long decay was only reported in the literature for auramine adsorbed in solid matrices. It was ascribed to the fraction of bound auramine in a region of compact coil of PMA.

Fluorescence of acridinic dyes in anionic surfactant solution.

The interaction of the cationic dyes acridine, 9-aminoacridine (9AA), and proflavine, with sodium dodecyl sulfate (SDS) was studied by electronic absorption, steady-state and time-resolved fluorescence spectroscopies. The dyes interact with SDS in the pre-micellar region leading in two cases to dimerization in dye-surfactant aggregates, but with distinct molecular arrangements. For proflavine, the observed red shift of the electronic absorption band indicates the presence of J-aggregate, which are nonfluorescent. In the case of 9AA, the aggregates were characterized as nonspecific (neither J- nor H-type is spectroscopically observed). The time-resolved emission spectra gives evidences of the presence of weakly bound dimers by the recovery of three defined decay times by global analysis: dye monomer (tau1 = 16.4 ns), dimer (tau2 = 7.1 ns), and a faster component (tau3 = 2.1 ns) ascribed to intracluster energy migration between monomer and dimer. Acridine has a weak interaction with SDS forming only an ion pair without further self-aggregation of the dye.

Excited-state intramolecular charge transfer in 9-aminoacridine derivative.

A new fluorochromic dye was obtained from the reaction of 9-aminoacridine with ethyl-2-cyano-3-ethoxyacrylate. It displays complex fluorescence that is ascribed to normal emission from the acridine chromophore in addition to excited-state intramolecular charge transfer (ESICT) formed upon light excitation. The analysis of the fluorescence decays in different solvents reveals two short-lived components in the range of 80-450 ps and 0.7-3.2 ns, ascribed to the formation and decay of the intramolecular charge transfer (ICT) state, in addition to a third component of about 9.0 ns, which is related to the normal emission from the acridine singlet excited state, probably in an enol-imine tautomeric form. The ICT emission is readily quenched by water addition to polar solvents, and this effect is ascribed to changes in the keto-amine/enol-imine equilibrium of this fluorochromic dye.

Solvent effects on the photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one.

The photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one was studied in different solvents and in SDS micelles. This compound presents characteristics which include an S(0)---> S(1) ( pi,pi*) transition with a (1)(n,pi*) perturbative component, due to the electronic coupling between the diethylamino group and the coumarin ring, considerable solvatochromism, dual fluorescence and high fluorescence quantum yields in almost all solvents studied. The electronic structure of the S(1) and S(2) excited states permits vibronic coupling between them, making configurational changes of the S(2) excited state possible, leading to the formation of an S(2)(TICT) state. Analysis of the TCSPC data indicates an equilibrium between the S(2)(TICT) and S(1)(LE) states in favour of the former. In protic solvents, the hydrogen bonding between the solvent and the diethylamino moiety results in the formation of an S(2)(HICT) state, making internal conversion an important deactivation process. Quantum mechanical calculations for the isolated molecule show that the diethylamino group in the S(2)(TICT) state is twisted at least 56 degree from the plane of the coumarin ring, with partial electronic decoupling between -NEt(2) and the coumarin ring. This twisting angle must be positively influenced by solute-solvent interactions. [capital Phi](ST) is found to be small, but not negligible. However, Phi (delta) can be considered negligible, an indication that T(1) is a short-lived state. Based on the experimental data and theoretical calculations, the most probable sequence for the first excited states, including the TICT state, is T(1)(n, pi*) < S(2)(TICT) < S(1)(pi,pi*) approximate S(2) (n,pi*).

Preparation of silver nanoprisms using poly(N-vinyl-2-pyrrolidone) as a colloid-stabilizing agent and the effect of silver nanoparticles on the photophysical properties of cationic dyes.

The synthesis of silver nanoprisms in aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) with different molecular weights (29, 55 and 1300 kg mol(-1)) as a stabilizing agent is described. Low molecular weight PVP (55 kg mol(-1)) is indicated for the preparation of a stable blue solution containing Ag nanoprisms via extended irradiation of a yellow colloidal solution of nanospheres with polychromatic visible light. The fluorescence properties of some cationic dyes (acridine, 9-aminoacridine, Nile Blue and auramine), free and bound to poly(methacrylic acid), have been studied in the presence of different shaped Ag colloidal particles in solution. Only auramine displays an amplification of the fluorescence signal with increasing colloid concentration, while the fluorescence of the other dyes is quenched by interaction with the polymer-stabilized metal nanoparticles.