Excited state properties of mixed phosphine 2-(2'-pyridyl)quinoline complexes of ruthenium(II)

Mixed ligand complexes of the type Ru(pq)(2)(PP)(2+) (pq = 2,2'-pyridylquinoline and PP = one bidentate or two monodentate phosphine ligands) have been prepared from the appropriate phosphine and Ru(pq)(2)Cl(2). The room temperature absorption spectra and low temperature (77 K) emission spectra, emission lifetimes, and quantum yields have been measured for the series of complexes and compared with those of Ru(pq)(3)(2+) and analogous Ru(bpy)(2)(PP)(2+) complexes (bpy = 2,2'-bipyridine) where possible. Emission spectra have been fit using a single mode Franck-Condon analysis. The visible absorption bands and emission bands are assigned to MLCT transitions that are blue shifted relative to Ru(pq)(3)(2+), while the emission lifetimes and quantum yields are increased. The trends in the nonradiative rate constants, k(nr), are described in terms of the energy gap, E(0), and the Huang-Rhys factor, S(M), which were obtained from the spectral fittings, and are correlated with the phosphine ligand structures.     

A theoretical, spectroscopic, and photophysical study of 2,7-carbazolenevinylene-based conjugated derivatives

A combined theoretical and experimental study of the structure, optical, and photophysical properties of four 2,7-carbazolenevinylene-based derivatives in solution is presented. Geometry optimizations of the ground states of PCP, PCP-CN, TCT, and TCT-CN were carried out using the density functional theory (DFT/B3LYP/6-31G*). It is found that PCP and TCT are nearly planar in their ground electronic states (S0), whereas the cyano derivatives are more twisted. The nature and the energy of the first singlet-singlet electronic transitions have been obtained from time-dependent density functional theory (TDDFT) calculations performed on the optimized geometries. For all the compounds, excitation to the S1 state corresponds mainly to the promotion of one electron from the highest-occupied molecular orbital to the lowest-unoccupied molecular orbital, and the S1 <-- S0 electronic transition is strongly allowed and polarized along the long axis of the molecular frame. The optimization (relaxation) of the first singlet excited electronic state (S1) has been done using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. It is observed that all four investigated compounds become more planar in their S1 relaxed excited state. Electronic transition energies from the relaxed excited states have been obtained from TDDFT calculations performed on the S1-optimized geometries. The absorption and fluorescence spectra of the carbazolenevinylenes have been recorded in chloroform. A good agreement is obtained between TDDFT vertical transitions energies and the (0,0) absorption and fluorescence bands. The change from phenylene to thiophene rings as well as the incorporation of cyano substituents induce bathochromic shifts in the absorption and fluorescence spectra. From the analysis of the energy of the frontier molecular orbitals, it is believed that thiophene rings and CN substituents induce some charge-transfer character to the first electronic transition, which is responsible for the red shifts observed. Finally, the fluorescence quantum yield and the lifetime of the compounds in chloroform have been obtained. In sharp contrast with many oligothiophenes, it is observed that TCT possesses a high fluorescence quantum yield. On the other hand, the CN-containing derivatives exhibit much lower fluorescence quantum yields, probably due to the combined influence of steric effects and charge-transfer interactions caused by the cyano groups.     

吩噻嗪-Corrole 镓(III)配合物的合成、荧光及其光断裂DNA性质

合成了吩噻嗪(PTZ)-corrole二元体1-3及其镓(III)配合物4-6.采用稳态吸收与稳态发射及时间分辨的瞬态光谱技术研究了这几种化合物的光物理特性.结合荧光量子产率和荧光寿命计算得到它们的辐射和无辐射速率常数.稳态吸收光谱表明:几种二元体中,corrole镓(III)单元表现出更强的Soret带和Q带.化合物1-3的荧光量子产率分别是0.156、0.134和0.139,辐射速率常数分别为4.02′107、3.47′107和2.89′107s-1.化合物4-6的荧光量子产率分别是0.502、0.443和0.494,辐射速率常数分别为20.90′107、16.78′107和21.11′107s-1.可见,化合物4-6的荧光量子产率和辐射速率常数均高于化合物1-3.然而,化合物4-6的荧光寿命分别是2.40、2.64和2.34ns,低于自由corrole1-3.琼脂糖凝胶电泳实验表明:在光照的条件下,这些吩噻嗪-corrole镓(III)二元体化合物能够把超螺旋DNA(formI)切割成缺刻型DNA(formII).     

First synthesis and electronic properties of cyano(oligo)phenothiazines

(Oligo)phenothiazinyl nitriles were synthesized in good to very good yields from bromo (oligo)phenothiazines via the Beller cyanation protocol either under conductive or under dielectric heating using NMP as a solvent. Their electronic properties were determined by absorption and emission spectroscopy and cyclic voltammetry. Cyano(oligo)phenothiazines display large Stokes-shifts (5800-8300 cm⁻¹) and substantial quantum yields (11-27%). Their reversible oxidation potentials are considerably shifted anodically due to the electron-withdrawing character of the cyano group.     

Spectral and photophysical studies on cruciform oligothiophenes in solution and the solid state

The photophysical and spectroscopic properties of a new class of oligothiophene derivatives, designated as cruciform oligomers, have been investigated in solution (room and low temperature) and in the solid state (as thin films in Zeonex matrixes). The study comprises absorption, emission, and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion, and singlet oxygen formation) and lifetimes. The overall data allow the determination of the rate constants for all decay processes. From these, several conclusions are drawn. First, in solution, the main deactivation channels for the compounds are the radiationless processes: S(1) --> S(0) internal conversion and S(1) --> T(1) intersystem crossing. Second, in general, in the solid state, the fluorescence quantum yields decrease relative to solution. A comparison is made with the analogous linear alpha-oligothiophenes, revealing a lower fluorescence quantum efficiency and, in contrast to the normal oligothiophenes, that internal conversion is an important channel for the deactivation of the singlet excited state. Replacement of thiophene by 1,4-phenylene units in the longer-sized cruciform oligomer increases the fluorescence efficiency. The highly efficient generation of singlet oxygen through energy transfer from the triplet state (S(Delta) approximately 1) provides support for the measured intersystem crossing quantum yields and suggests that reaction with this may be an important pathway to consider for degradation of devices produced with these compounds.     

Blue phosphorescence from mixed cyano-isocyanide cyclometalated iridium(III) complexes

The synthesis, structure, and photophysical and electrochemical properties of cyclometalated iridium complexes with ancillary cyano and isocyanide ligands are described. In the first synthetic step, cleavage of dichloro-bridged dimers [Ir(N=C)2(mu-Cl)]2 (N=C = 2-phenylpyridine, 2-(2-fluorophenyl)pyridine, and 2-(2,4-difluorophenyl)pyridine) by isocyanide ligands gave monomeric species of the types Ir(N=C)2(RNC)(Cl) (RNC = t-butyl isocyanide, 1,1,3,3-tetramethylbutyl isocyanide, 2-morpholinoethyl isocyanide, and 2,6-dimethylphenyl isocyanide). In turn, the chloride was replaced by cyanide giving Ir(N=C)2(RNC)(CN). The X-ray structures for two of the complexes show that the trans-pyridyl/cis-phenyl geometry of the parent dimer is preserved, with the ancillary ligands positioned trans to the cyclometalated phenyls. The cyano complexes all display strong blue photoluminescence in ambient, deoxygenated solutions with the first lambdamax ranging from 441 to 458 nm, quantum yields spanning 0.60 to 0.75, and luminescent lifetimes of 12.0-21.4 mus. A lack of solvatochromism and highly structured emission indicate that the lowest energy excited state is triplet ligand centered with some admixture of singlet metal-to-ligand charge-transfer character.     

New metallodendrimers containing an octakis(diphenylphosphino)-functionalized silsesquioxane core and ruthenium(II)-based chromophores

A new class of surface-modified dendrimers has been prepared by reactions of 8 equiv of the terpyridine-functionalized polyether monodendrons with a polyhedral oligomeric silsesquioxane (POSS) core. Subsequent reactions of these spherically shaped organic dendrimers with Ru(II)-based precursors afford photo- and redox-active metallodendrimers. These new dendrimers have been characterized using a combination of mass spectral analysis (MALDI-TOF/MS, ESI/MS, and FAB/MS), nuclear magnetic resonance (1H, 13C, 29Si, and 31P(1H) NMR), photophysical analyses (electronic absorption, emission, excited-state lifetime, and quantum yield) and electrochemical measurement (cyclic voltammetry). Specifically, 31P(1H) NMR is used to monitor the completion of reactions and the purity of dendrimers and metallodendrimers. These new metallodendrimers exhibit large extinction coefficients that coincide with the number of peripheral Ru(II)-based chromophores. With the use of (-CH2-Ph-tpy)RuII(bpy)2 type of chromophores, all metallodendrimers are found emissive at room temperature, with lifetimes in the range of 605-890 ns. Photophysical data also indicate similar steady-state emission maxima and single-exponential decay kinetics for all metallodendrimers, and the observed overall quantum yields of the G1, G2, and G3 metallodendrimers are found to be 14, 20, and 7 times higher than that of the monomeric model complex (CH3-Ph-tpy)Ru(bpy)2(PF6)2. Electrochemical studies reveal the presence of surface-confined species, in addition to the ligand-centered and metal-centered redox processes.     

Synthesis and photophysical properties of N-fused tetraphenylporphyrin derivatives: near-infrared organic dye of [18]annulenic compounds

A variety of N-fused porphyrin derivatives were prepared and their photophysical properties were investigated. Although intact N-fused tetraarylporphyrins showed almost no emission, introduction of electron-withdrawing groups such as a nitro group and a cyano group on the macrocycles caused significant refinements in their emission efficiency. Long emission wavelengths (900-1000 nm) as well as fairly large Stokes shifts (～1200 cm(-1)) are exceptionally unique photophysical properties among [18]annulenic compounds, which could be rationalized by the excited state intramolecular proton transfer (ESIPT) process. Relatively weak emission quantum yields (～5.0 × 10(-4)) and unusually short S(1) state lifetimes (～13.5 ps) are in good agreement with the ESIPT process. The solvent and substituent effects on the photophysical properties are also discussed in conjunction with the theoretical studies, where the mesityl groups at the meso-positions play a unique role.     

Tuning the excited-state properties of [M(SnR3)2(CO)2(alpha-diimine)] (M = Ru, Os; R = Me, Ph)

The influences of R, the alpha-diimine, and the transition metal M on the excited-state properties of the complexes [M(SnR3)2(CO)2(alpha-diimine)] (M = Ru, Os; R = Ph, Me) have been investigated. Various synthetic routes were used to prepare the complexes, which all possess an intense sigma-bond-to-ligand charge-transfer transition in the visible region between a sigma(Sn-M-Sn) and a pi*(alpha-diimine) orbital. The resonance Raman spectra show that many bonds are only weakly affected by this transition. The room-temperature time-resolved absorption spectra of [M(SnR3)2(CO)2(dmb)] (M = Ru, Os; R = Me, Ph; dmb = 4,4'-dimethyl-2,2'-bipyridine) show the absorptions of the radical anion of dmb, in line with the SBLCT character of the lowest excited state. The excited-state lifetimes at room temperature vary between 0.5 and 3.6 microseconds and are mainly determined by the photolability of the complexes. All complexes are photostable in a glass at 80 K, under which conditions they emit with very long lifetimes. The extremely long emission lifetimes (e.g., tau = 1.1 ms for [Ru(SnPh3)2(CO)2(dmb)]) are about a thousand times longer than those of the 3MLCT states of the [Ru(Cl)(Me)(CO)2(alpha-diimine)] complexes. This is due to the weak distortion of the former complexes in their 3SBLCT states as seen from the very small Stokes shifts. Remarkably, replacement of Ru by Os hardly influences the absorption and emission energies of these complexes; yet the emission lifetime is shortened because of an increase of spin-orbit coupling. The quantum yield of emission at 80 K is 1-5% for these complexes, which is lower than might be expected on the basis of their slow nonradiative decay.     

Bis(BF2)-2,2'-bidipyrrins (BisBODIPYs): highly fluorescent BODIPY dimers with large stokes shifts

Four new dimeric bis(BF(2))-2,2'-bidipyrrins (bisBODIPYs), and their corresponding BODIPY monomers, have been prepared and studied with respect to their structural and photophysical properties. The solid-state molecular structure of the dimers and the relative orientation of the subunits have been revealed by an X-ray diffraction study, which showed that the molecules contain two directly linked BODIPY chromophores in a conformationally fixed, almost orthogonal arrangement. Two of the fluorine atoms are in close contact with each other and the (19)F NMR spectra show a characteristic through-space coupling in solution. The new chromophores all exhibit a clear exciton splitting in the absorption spectra with maxima at about 490 and 560 nm, and are highly luminescent with an intense emission band at around 640 nm. The Stokes shift, which is the difference between the maximum of the lowest-energy absorption band and the maximum of the emission band, has a typical value of 5 to 15 nm for simple BODIPYs, whereas this value increases to 80 nm or more for the dimers, along with a slight decrease in fluorescence quantum yields and lifetimes. These properties indicate potential uses of these new fluorophoric materials as functional dyes in biomedical and materials applications and also in model compounds for BODIPY aggregates.     

Luminescence properties of Pt(II) complexes containing polypyridine ligands with extended aromatic moieties

The luminescence properties of eleven Pt(ii) complexes containing polypyridine ligands with extended aromatic moieties have been studied, both in acetonitrile fluid solution at 298 K and in butyronitrile rigid matrix at 77 K. For comparison purposes, also the phosphorescence properties of three free ligands at 77 K in butyronitrile have been investigated. The absorption spectra of all the compounds exhibit intense bands (epsilon in the range 10(4)-10(5) M(-1) cm(-1)) in the UV region, which are attributed to spin-allowed ligand-centered (LC) transitions, and moderately intense bands (epsilon in the range 10(3)-10(4) M(-1) cm(-1)) in the visible region, which receive contribution from both spin-allowed LC transitions and spin-allowed metal-to-ligand charge-transfer (MLCT) transitions. At low energy, less intense spin-forbidden MLCT bands are also present. At 77 K in rigid matrix, all the studied compounds exhibit structured and long-lived (lifetimes from 840 mus on the millisecond timescale) luminescence, which is attributed to triplet LC states in all cases. At room temperature in fluid solution the luminescence lifetime of all the compounds is largely shortened (nanosecond timescale), and most of the emission spectra are unstructured and red-shifted. For species exhibiting structured emission spectra even at room temperature, low luminescence quantum yields are always obtained (Phi < 10(4)), and their emission is assigned to triplet LC states, which mainly deactivate to the ground state by thermal-activated surface crossing to a closely-lying metal-centered (MC) triplet state. Compounds exhibiting unstructured emission show relatively high emission quantum yields (about 0.1) and their emission is assigned to a mixed LC/MLCT state.     

Radiative relaxation of Sepia eumelanin is affected by aggregation.

The steady‐state and time‐resolved emission properties of aqueous solutions containing different aggregation state distributions of eumelanin are reported. Excitation spectra of the size‐selected samples reveal, for the first time, differences in absorption bands due to varying levels of aggregation. These size‐dependent absorption properties result in size‐dependent emission band shapes and quantum yields. For all size fractions, absorption and emission overlap significantly. The emission yield for small eumelanin aggregates is 5.7 times greater than that for large eumelanin aggregates. Time‐resolved population decays reveal that small eumelanin aggregates are responsible for long‐lived emission dynamics (lifetimes greater than 1 ns), while large eumelanin aggregates are the source of short emission decay (lifetimes less than 1 ns). Polarized emission decays for the large and small aggregates reveal that energy transfer occurs both within the same and between the separate fundamental building blocks of eumelanin. The observed energy transfer dynamics can be accounted for using Förster theory.     

Intramolecular proton-transfer processes starting at higher excited states: a fluorescence study on 2-butylamino-6-methyl-4-nitropyridine N-oxide in nonpolar solutions

This article describes the exceptional photophysics of 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M). It is known from the literature that this compound may undergo excited-state intra- or intermolecular proton-transfer reactions. In nonpolar solvents, 2B6M exhibits an unusual fluorescence behavior: there is a substantial difference between the relative band intensities of the excitation and absorption spectra. Furthermore, in emission two bands are observed, and their relative intensities depend on the excitation wavelength, thus violating the Kasha-Vavilov rule. It is the objective of this research to interpret these results. For this purpose, steady-state fluorescence excitation and emission spectra in the liquid state were recorded and quantum yields were determined for the two types of emission. In addition, absorption spectra were measured at room temperature and under low-temperature conditions. Finally, fluorescence lifetimes of the emitting species were determined using the time-correlated single photon counting technique. The results suggest that in the liquid state only one (monomeric) ground state species dominates, which can emit via two different pathways (from the normal and the tautomeric excited state). The excitation spectra point at two different internal proton-transfer processes, one starting at the S1 state and one starting at the S2 state. On the basis of the measured lifetimes and fluorescence quantum yields, a kinetic scheme was completed that can quantitatively explain the observations.     

Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

A comprehensive photophysical and spectroscopic study of a new class of p-phenylenevinylene oligomers (PPV-trimers) possessing different alkyl and alkyloxy sidechain substituents and different end groups (aldehyde, CC, phenylene and anthracene units) was undertaken in solution at room temperature (293 K), low temperature (77 K) and in thin films. The study comprises absorption, emission and triplet–triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion and singlet oxygen formation) and lifetimes. The data allow the determination of rate constants for all decay processes. From these, several conclusions could be drawn. Changing from alkyl to alkyloxy substituents does not change fluorescence and internal conversion yields but decreases the (already small) intersystem crossing yield. The introduction of anthracene at the terminal ends of the PPV-trimers leads to the lowest fluorescence yield reported in this study. Of particular importance is the fact that the fluorescence quantum yields in films are of the same order of magnitude as those in solution, which suggests the potential for use of these oligomers for light-emitting device applications. With one of the alkyloxy derivatives, a more detailed study of the early part of the fluorescence decay was made, and it was found that upon excitation a fast conformational relaxation process of the initially excited oligomer occurs, leading to a more planar conjugation segment.     

Photophysical properties of closely-coupled, binuclear ruthenium(II) bis(2,2':6',2''-terpyridine) complexes

The photophysical properties of closely-coupled, binuclear complexes formed by connecting two ruthenium(II) bis(2,2':6',2'-terpyridine) complexes via an alkynylene group are compared to those of the parent complex. The dimers exhibit red-shifted emission maxima and prolonged triplet lifetimes in deoxygenated solution. Triplet quantum yields are much less than unity and the dimers generate singlet molecular oxygen with low quantum efficiency. Temperature dependence emission studies indicate coupling to higher-energy triplet states while cyclic voltammetry shows that the metal centres are only very weakly coupled but that extensive electron delocalization occurs upon one-electron reduction. The radiative rate constants derived for these dimers are relatively low, because the lowest-energy metal-to-ligand, charge-transfer states possess increased triplet character. In contrast, the rate constants for nonradiative decay of the lowest-energy triplet states are kept low by extended electron delocalization over the polytopic ligand. The poor triplet yields are a consequence of partitioning at the second triplet level.     

Synthesis of water-soluble, ring-substituted squaraine dyes and their evaluation as fluorescent probes and labels

A series of ring-substituted squaraines absorbing and emitting in the red and NIR spectral region was synthesized and their spectral and photophysical properties (quantum yields, fluorescence lifetimes) and photostabilities were measured and compared to Cy5, a commonly used fluorescent label. The absorption maxima in aqueous media were found to be between 628 and 667 nm and the emission maxima are between 642 and 685 nm. Squaraine dyes exhibit high extinction coefficients (163,000–265,000 M⁻¹ cm⁻¹) and lower quantum yields (2–7%) in aqueous buffer but high quantum yields (up to 45%) and long fluorescence lifetimes (up to 3.3 ns) in presence of BSA. Dicyanomethylene- and thio-substituted squaraines exhibit an additional absorption around 400 nm with extinction coefficients between 21,500 and 44,500 M⁻¹ cm⁻¹. These dyes are excitable not only with red but also with blue diode lasers or light emitting diodes. Due to the favourable spectral and photophysical properties these dyes can be used as fluorescent probes and labels for intensity- and fluorescence lifetime-based biomedical applications.     

Spectral and photophysical characterization of donor-pi-acceptor arylthienyl- and bithienyl-benzothiazole derivatives in solution and solid state

A comprehensive study has been made in solution at room temperature (293 K), low temperature (77 K), and in thin films (Zeonex matrixes) of the spectral and photophysical properties of six arylthienyl- and bithienyl-benzothiazole derivatives functionalized with different donor groups. Similar experiments have been carried out with two related precursors (containing the arylthienyl and aryl-bithienyl conjugated systems), and results are compared. Singlet-singlet and triplet-triplet absorption spectra, emission spectra together with lifetimes and quantum yields have been obtained, and from these data the rates for all the radiative and nonradiative processes determined, providing information on the dominant decay processes. The arylthienyl-benzothiazole derivatives show high fluorescence quantum yields (phi(F)) with negligible internal conversion (phi(IC)), whereas the bithienyl-benzothiazoles display lower but still significant phi(F) values, but now radiationless processes (phi(IC) and phi(ISC)) are competitive. A comparison with the analogous oligothiophenes is made. Singlet oxygen yields were also determined and the triplet energy transfer to (3)O2 to produce (1)O2 was found to be highly efficient with values of S(Delta)(= phi(Delta)/phi(T)) varying from 0.4 to 1.     

Photochemistry and photophysics of thienocarbazoles

Two methylated thienocarbazoles and two of their synthetic nitro-precursors have been examined by absorption, luminescence, laser flash photolysis and photoacoustic techniques. Their spectroscopic and photophysical characterization involves fluorescence spectra, fluorescence quantum yields and lifetimes, and phosphorescence spectra and phosphorescence lifetimes for all the compounds. Triplet-singlet difference absorption spectra, triplet molar absorption coefficients, triplet lifetimes, intersystem crossing S1 --> T1 and singlet molecular oxygen yields were obtained for the thienocarbazoles. In the case of the thienocarbazoles it was found that the lowest-lying singlet and triplet excited states, S1 and T1, are of pi,pi* origin, whereas for their precursors S1 is n,pi*, and T1 is pi,pi*. In both thienocarbazoles it appears that the thianaphthene ring dictates the S1 --> T1 yield, albeit there is less predominance of that ring in the triplet state of the linear thienocarbazole, which leads to a decrease in the observed phiT value.     

以铱配合物为核、聚(芴-咔唑)为臂的白光星型磷光聚合物

设计合成了以苯基苯并咪唑和吡啶三唑为配体的高效的黄绿光铱配合物(M1),并通过Suzuki缩聚反应制备了以磷光铱配合物客体为中心核、蓝光荧光聚(芴-咔唑)主体为臂的星型磷光聚合物(P2.5、P5.0和P10),着重对M1和聚合物的发光性能、电化学性能及热稳定性能进行研究。 结果表明,M1具有较高的荧光量子效率(32.06%),其荧光寿命为1.09 μs,聚合物荧光寿命为2.223.93 μs,均表现为磷光;通过调节主客体的比例,利用主客体的部分能量转移机制,来实现聚合物的不同光色,发光颜色可从蓝光向黄光变化;当M1摩尔分数为2.5%时,获得的白光聚合物(P2.5)具有较好的发光性能和热稳定性能,色坐标为(0.30,0.32),位于白光区域,其最高占有轨道(HOMO)能级和最低未占有轨道(LUMO)能级分别为5.49和2.43 eV,荧光量子产率为14.3%,荧光寿命为2.22 μs。     

The synthesis and the solvent and substituent effect on the spectroscopic characteristic of 3-ethyl-2-(p-substitued styryl)benzothiazolium iodides

The photophysical and photochemical properties of p-substitued 2-styryl-ethylbenzothiazolium iodides, possessing different electron-withdrawing or electron-donating groups are described. The dyes were prepared by the condensation of 3-ethyl-2-methylbenzothiazole salts with p-substituted benzaldehydes. The synthesis of suitable substrates is presented as well. We describe here the absorption, emission spectra and the luminescence quantum yield of hemicyanine dyes (SH) measured in 11 different organic solvents of varying polarity. Molecular structure of the synthesized dyes was established by (1)H NMR, electronic absorption and fluorescence spectrometry. The spectral data confirmed that all the compounds exist in E-configuration of their styryl residues. The planar molecular conformation is typical for the compounds with five-membered side aromatic moieties (for example benzothiazole). The compounds possessing N-alkyl substituent in phenyl ring, in contrast to the compounds with other substituents, exhibit low fluorescence quantum yield in THF solution. This indicates that for N-alkyl derivatives the non-radiative processes are much more effective than the radiative ones. The electronic absorption and fluorescence emission spectra of tested dyes demonstrate high sensitivity to the nature of substituent introduced into the aromatic ring.