Photophysical properties of 9,10-disubstituted anthracene derivatives in solution and films

We have carried out absorption, time-resolved fluorescence, and fluorescence quantum yield measurements of four new soluble anthracene derivatives. They show natural radiative lifetimes in the range of 2.5-4.4 ns, which is 5-10 times shorter than those reported for unsubstituted anthracene. The 9,10-bis(phenylethynyl)anthracene (BPEA) derivatives show the largest fluorescence transition dipoles, which is attributed to extended π-conjugation between anthracene and phenyls through acetylene linkages. Spin-cast films of the BPEA derivatives show strong fluorescence quenching by weakly emitting low energy excitations, which is attributed to excimer-like traps. Quenching is significantly reduced when bulky dendrons are attached so that they give maximum coverage of the emitting chromophore and prevent their aggregation. The results show that anthracene derivatives can be developed into efficient solution-processable fluorescent emitters for the blue and green spectral regions.     

Photophysical properties of borondipyrromethene analogues in solution

The photophysical properties of seven new 8-(p-substituted)phenyl analogues of 4,4-difluoro-3,5-dimethyl-8-(aryl)-4-bora-3a,4a-diaza-s-indacene (derivatives of the well-known fluorophore BODIPY) in several solvents have been studied by means of absorption and steady-state and time-resolved fluorimetry. For each compound, the fluorescence quantum yield and lifetime are lower in solvents with higher polarity owing to an increase in the rate of nonradiative deactivation. Increasing the electron withdrawing strength of the p-substituent on the phenyl group in position 8 also leads to lower fluorescence quantum yields and lifetimes. When the p-substituent on the phenyl group in position 8 is a tertiary amine [8-(4-piperidinophenyl), 8-(4-N,N-dimethylaminophenyl), and 8-(4-morpholinophenyl)], the low quantum yields of these compounds in more polar solvents can be rationalized by the inversion of the energy levels of an apolar, highly fluorescent and a polar, nonfluorescent excited state, where charge transfer from the tertiary amine to the BODIPY unit occurs. These amine analogues can be protonated at low pH in aqueous solution. Fluorescence titrations yielded pK(a) values of their conjugate ammonium salts which are in agreement with the electron donating tendency of the amine group: piperidino (4.15) > dimethylamino (2.37) > morpholino (1.47), with the pK(a) values in parentheses. The rate constant of radiative deactivation (k(f)) is the same for all compounds in all solvents studied (k(f) = 1.4 x 10(8) s(-1)).     

Photophysical properties of novel water soluble fullerene derivatives

The spectroscopic and photophysical properties for a series of bis-adduct derivatives of C₆₀ have been studied using a combination of time-resolved and steady state techniques, including picosecond single photon counting and laser flash photolysis. The electronic absorption and fluorescence spectra are red shifted with respect to those of C₆₀. As with the parent fullerene, the main deactivation channel of the excited singlet state is intersystem crossing with the yields of singlet oxygen ranging from 0.63 to 0.97. Our results demonstrate that the photophysical properties depend on the addition pattern of the addends.     

Syntheses of soluble, pi-stacking tetracene derivatives

[reaction: see text] The syntheses of a series of fluorine- and alkyl/alkoxy-functionalized tetracenes are reported. These functional groups are found to improve the solubility in common organic solvents and tune molecular arrangement in solids. The crystal packing, electrochemical behavior, and UV-vis absorbance spectroscopy of these materials are discussed.     

Photophysical properties of BODIPY-derived hydroxyaryl fluorescent pH probes in solution.

The photophysical properties of five fluorescent pH probes derived from 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene with phenolic or naphtholic subunits at position 8 and with substituents having different electron driving forces at positions 3 and 5 have been investigated in several organic solvents, by means of absorption, steady-state, and time-resolved fluorimetry. For each compound, the fluorescence quantum yield and lifetime are lower in solvents with higher polarity, owing to an increase in the rate of nonradiative deactivation. The rate constants for radiative deactivation, k(f), are nearly constant for all dyes in all solvents studied [k(f)=(1.7+/-0.2)x10(8) s(-1)]. In aqueous solution, these probes undergo a reversible protonation-deprotonation in the near-neutral to basic pH range, producing intensity increases with lower pH. The pK(a) values of the indicators are between 7.5 and 9.3, depending on the substitution pattern on positions 3, 5, and 8. The difference between the absorption and excitation spectra as a function of pH is indicative of the presence of two species in aqueous solution: the phenol- or naphthol-based indicator and its conjugate base.     

Photophysical properties of benzil in solution: triplet state deactivation pathways

The fluorescence and phosphorescence from benzil in dilute benzene and cyclohexane solutions (2 × 10⁻⁴ M) were studied by both conventional luminescence and time-correlated single-photon techniques in the temperature range 8 – 69 °C. The fluorescence (λ = 502 nm) did not show a substantial temperature dependence and was free from thermal and triplet-triplet annihilation delayed contributions at the low concentration used. The phosphorescence (λ = 562 nm) was temperature dependent and its decay was controlled by an activation energy (E_a = 7.4 ± 0.5 kcal mol⁻¹) which was slightly larger than the spectroscopic single-triplet splitting (6.1 kcal mol⁻¹). The photophysical parameters derived from the lifetimes of the two emissions was not consistent with the model of thermal equilibration between S₁ and T₁.     

Photophysical properties and photochemical rearrangement of single crystal salicylideneaniline in solution

Salicylideneaniline originally crystallized from a solution has lemon yellow color. Irradiation with near ultraviolet causes the color change from yellow to red. The red state changes spontaneously back to yellow in 2ms. This change is accelerated by visible light. Kinetic data are reported in the temperature range between 10 and 60 degrees C, for the dark fading reactions of the colored isomers formed by the near ultraviolet irradiation. Observed the decay kinetics was first order reactions. Activation energies and entropies of activation are reported for ethanol. The observation of T-T absorption and emission were complicated due to the colored isomer formation during the optical pumping.     

Photophysical properties of carborane-containing derivatives of 5,10,15,20-tetra(p-aminophenyl)porphyrin

Absorption, fluorescence emission, fluorescence excitation spectra and fluorescence decay kinetics of carborane derivatives of 5,10,15,20-tetra(p-aminophenyl)porphyrin have been investigated. Carborane derivatives are prepared by acylation of the amino groups of 5,10,15,20-tetra(p-aminophenyl)porphyrin by 9-carboranyl acetyl chloride. From the analysis of the absorption and fluorescence spectra, it is concluded that covalent linking of carborane molecules to the tetraphenylporphyrin molecule significantly changes the self-conjugated pi-system of the porphyrin macrocycle: positions of maxima of absorption and fluorescence spectra shift to the red region by 3-8 nm; the halfwidths of these bands are broadened by 2.5-5.0 nm; the relative intensity of the bands I-IV also changes. The fluorescence decay kinetics of the carborane derivatives are biexponential. According to the experimental data and model simulation, it is concluded that the intramolecular electron transfer proceeds from the porphyrin excited part of the molecule to carboranyls with a rate constant of 415 ps(-1) and efficiency of 0.16-0.8. Recombination of separated charges occurs within 1.4 ns.     

Photophysical and self-assembly properties of asymmetrical multi-aralkyl and arylaldehyde substituted pyrene derivatives

A series of novel asymmetrical pyrene derivatives with aralkyl and aldehyde groups have been successfully synthesized, and their spectroscopic parameters were investigated detailedly. The effects of aralkyl substituent amounts on the electronic absorption and emission spectra have been explored in evaluation of their potential as optical materials components. Moreover, the electrochemical properties of the new pyrene derivatives have been studied for the molecules' HOMO and LUMO levels by cyclic voltammograms. In particular, titration of anhydrous ethanol into dilute CH₂Cl₂ solution of above compounds, an unusual change of the fluorescence value was observed. The change is believed to correlate strongly to intermolecular charge transfer. The morphological evolution of self-assembled pyrene derivatives with (arylethynyl)aldehyde substituents, from tamen-distinct-like morphologies to vesicular textures, was obtained by increasing aralkyl-substituted fragments. These asymmetrical discotic compounds represent an interesting set of candidates for optoelectronic device components.     

Self-assembly of soluble anthracene, tetracene and pentacene derivatives

New soluble disubstituted acenes (tetracene, pentacene) have been designed in order to mimic 2,3-alkoxy derivatives of anthracene. They have been shown to self-assemble and gellify a large variety of organic solvents. This process involves the formation of nano-fibres through non-covalent molecular interactions (van der Waals, π-π stacking), weaving a three-dimensional supramolecular network. Efficient transfer of excitation energy through these nano-structures has been evidenced in an anthracene light-harvesting matrix doped with less than 1 mol% of a tetracene energy trap.     

Photovoltaic properties of tetracene and pentacene layers

Photovoltaic phenomenon in tetracene and pentacene layers evaporated under the same conditions onto a glass substrate and provided with the same couple of electrodes is investigated. Comparison of the results obtained for both organic materials makes it possible to conclude that in spite of differences in mechanisms of charge carrier generation, the values of photovoltaic parameters are very similar.     

Photophysical processes of some benzimidazole derivatives

The photophysical properties of N-(alpha-naphthyl)-benzimidazole (alpha-NABI), N-(beta-naphthyl)-benzimidazole (beta-NABI) and N-(alpha-pyridyl)-benzimidazole (alpha-PYBI) were studied and alpha-NYBI exhibit intramolecular charge transfer fluorescence in polar solvents. The fluorescence of benzimidazoles can be quenched by acetic acid and the existence of exciplexes was observed between the benzimidazole derivatives and acetic acid. Particularly, the maximum emission peak of solution of alpha-PYBI in mixed solvent, ether and acetic acid, presents obvious red-shift with the increase of concentration of acetic acid in the mixed solvent.     

Photophysical properties of gatifloxacin in aqueous solution by laser flash photolysis and pulse radiolysis

GFX in water, at pH 7.0, shows intense absorption bands with peaks at 284 and 333 nm, (ε=24,670 and 12,670 M⁻¹ cm⁻¹). Both the absorption and emission properties of GFX were pH-dependent; the pK_a values for the protonation equilibria of the ground state (5.7 and 8.9) and excited singlet state (3.6 and 7.5) of GFX were determined spectroscopically. GFX fluoresces weakly, with a maximum quantum yield for fluorescence emission (0.06) at pH 4.7. A series of experiments were performed to characterize the transient species of GFX in aqueous solution using laser flash photolysis and pulse radiolysis. GFX undergoes monophotonic photoionization with a quantum yield of 0.16 on a 355 nm laser excitation. This process leads to the formation of a long-lived cation radical with a maximum absorption at 380 nm. Triplet-triplet absorption had maximum absorption at 510 nm. The reaction of GFX with one-electron oxidant N₃• was investigated and the bimolecular rate constant was determined to be 3.1×10⁹ M⁻¹ s⁻¹.     

Photophysical, photochemical, and tumor-selectivity properties of bromine derivatives of rhodamine-123

The conceptual basis for the development of mitochondrial targeting as a novel therapeutic strategy for both chemotherapy and photochemotherapy of neoplastic diseases rests on the observation that enhanced mitochondrial membrane potential is a common tumor cell phenotype. The potential of this strategy is highlighted by the fact that the toxic effects associated with a number of cationic dyes known to localize in energized cell mitochondria are much more pronounced in tumor cells than in normal cells. Here we evaluate the phototoxic properties of four bromine derivatives of rhodamine-123 toward human uterine sarcoma (MES-SA) and green monkey kidney (CV-1) cells and compare the degrees of tumor cell selectivity associated with these dyes with those associated with two model mitochondrial triarylmethanes (crystal violet and ethyl violet). Selective phototoxicity toward tumor cells was found to be highly dependent upon the lipophilic/hydrophilic character of the cationic photosensitizer. Our experimental data have indicated that the probability of success of mitochondrial targeting in (photo)chemotherapy of neoplastic diseases is higher when the octan-1-ol/water partition coefficient of the drug candidate falls within approximately two orders of magnitude from that of the prototypical mitochondria-specific dye rhodamine-123.     

Photophysical properties of corrphycenes

The photophysical properties of the Zn salt of octaethylcorrphycene (compound 1) and the doubly protonated octaethylcorrphycene (compound 2) were determined in benzene solutions. Fluorescence spectra and fluorescence quantum yields of phiF (1) = 0.03+/-0.02 and PF (2) = 0.06+/-0.02 were measured. The triplet-triplet absorption spectra were obtained by means of flash-photolysis experiments. The triplet quantum yield values phiT (1) = 0.79+/-0.08 and phiT (2) = 0.82+/-0.08 were obtained by using laser-induced optoacoustic spectroscopy. The quantum yield of singlet molecular oxygen generation in air-saturated solutions, phidelta (1) = 0.55+/-0.07 and phidelta (2) = 0.38+/-0.05, were also measured using time resolved NIR luminescence.     

Photophysical properties of ricin

The molar absorption coefficient of ricin in phosphate-buffered saline (PBS) at 279 nm was measured as (93,900+/-3300) L mol(-1) cm(-1). The concentration of ricin was determined using amino acid analysis. The absorption spectrum of ricin was interpreted in terms of 69% contribution from absorption by tryptophan residues and 31% contribution from absorption by tyrosine residues. The total dipole strength of the ricin band at 280 nm was determined to be (147+/-8) D2 and was consistent with the combined dipole strengths of 10 tryptophan ([11.7+/-1.0] D2) and 23 tyrosine ([1.4+/-0.2] D2) residues. The structure of ricin was used to determine the coupling of the tryptophan residues in ricin. The maximum interaction energy was found to be 424 cm(-1)/epsilon while the average interaction between any two pairs of tryptophan residues was approximately 18 cm(-1)/epsilon. In this study, epsilon is the dielectric constant inside the protein. The fluorescence from ricin, excited at 280 nm, was dominated by fluorescence from tryptophan residues suggesting the presence of energy transfer from tyrosine to tryptophan residues. The absorbance and fluorescence of ricin increased slightly when ricin was denatured in a high concentration of guanidine. Irreversible thermal unfolding of ricin occurred between 65 degrees C and 70 degrees C. (D=3.3364*10(-30) Cm, not SI unit, convenient unit for the magnitude of the electric dipole moment of molecules.).     

Photophysical properties of novel ferrocenyl quinoline derivatives with red emission in solutions and polymeric matrices

A group of novel 2-ferrocenyl quinoline derivatives was designed and their photophysical properties were thoroughly studied. UV-VIS and steady-state fluorescence spectra show that these compounds gain energy in the ultra-violet region and give red emissions in different organic solvents. More importantly, two transparent hybrid thick films composed of 2-ferrocenyl quinoline and poly[1-(methoxycarbonyl)-1-methylethylene] (poly(methyl 2-methylpropenoate, (poly(methyl methacrylate), PMMA), or poly[2-hydroxyethyl 2-methylprop-2-enoate] (poly(2-hydroxyethyl methacrylate), PHEMA) matrix were successfully prepared. Both films showed red emissions of ferrocenyl quinoline chromophore and the ideal composition of luminescent species is 10⁻⁶ M PMMA and 10⁻⁵ M PHEMA, respectively. SEM graph exhibited ferrocenyl quinoline molecules dispersed very homogenously within the above polymer hosts.     

Photophysical properties of lumichromes in water

The photophysics of lumichrome, 1-methyllumichrome, and lumiflavin in water solutions have been investigated. Fluorescence lifetimes of 2.7 and 2.2 ns were observed for lumichrome and 1-methyllumichrome, respectively, the corresponding triplet state lifetimes of 17 and 18 μs have been obtained from the transient absorption spectra. Evidence for long lived species with absorption maxima near 450 nm and lifetimes of ca. 400 μs has been found in the transient absorption spectra of both lumichromes. Quantum yields for the sensitised production of singlet oxygen, φ_Δ, are 0.36 and 0.41 for lumichrome and 1-methyllumichrome, respectively, in D₂O.     

Photophysical properties of PPP and PPV derivatives bearing polystyrene or polycaprolactone as side groups

This contribution reports on detailed photophysical investigations of poly(p-phenylene) PPP and poly(p-phenylene-vinylene) (PPV) derivatives laterally decorated with polystyrene (PPV-PSt) or poly(ε-caprolactone) (PPP-PCL, PPP-altPCL, PPV-PCL and PPV-PCL-Br). The polymers emit blue and exhibit very high relative and absolute photoluminescence quantum yield, Φ_f, in dilute solution, thin film (spin-coated and inkjet-printed) and bulk state. This is ascribed to the presence of the lateral macromolecules, which suppress the strong π-π interactions and consequently excimers formation. Lower Φ_f value was obtained for the bromine containing polymer and its corresponding model compound dibromodistyrylbenzene Br₂-DSB, which was ascribed to heavy atom effect enabling intersystem crossing from S₁ to T₁. However, studies at 77 K did not reveal phosphorescence, in contrast an enhancement of the fluorescence intensity with respect to room temperature measurement was observed.