Lippert-Mataga Plots Research Articles

Tunable Fluorescence via Self-Assembled Switching of AIE-Active Micelle-like Nanoaggregates.

Chemical structures bearing a combination of aggregation-induced emission enhancement (AIEE) and intramolecular charge transfer (ICT) properties attracted the attention of many researchers. Recently, there is an increasing demand to pose tunable AIEE and ICT fluorophores that could present their conformation changes-related emission colors by adjusting the medium polarity. In this study, we designed and synthesized a series of 4-alkoxyphenyl-substituted 1,8-naphthalic anhydride derivatives NAxC using the Suzuki coupling reaction to construct donor-acceptor (D-A)-type fluorophores with alkoxyl substituents of varying carbon chain lengths (x = 1, 2, 4, 6, 12 in NAxC). To explain the observation that molecules with longer carbon chains revealed unusual fluorescence enhancement in water, we study the optical properties and evaluate their locally excited (LE) and ICT states by solvent effects combined with Lippert-Mataga plots. Then, we explored the self-assembly abilities of these molecules in water-organic (W/O) mixed solutions and observed the morphology of its nanostructure using a fluorescence microscope and SEM. The results show that NAxC, x = 4, 6, 12 show different degrees of self-assembly behaviors and corresponding aggregation-induced emission enhancement (AIEE) progresses. At the same time, different nanostructures and corresponding spectral changes can be obtained by adjusting the water ratio in the mixed solution. That is, NAxC compounds present different transitions between LE, ICT and AIEE based on the polarity, water ratio and time changes. We designed NAxC as the structure-activity relationship (SAR) of the surfactant to demonstrate that AIEE comes from the formation of micelle-like nanoaggregates, which causes a restriction of the transfer from the LE state to the ICT state, and micelle formation results in a blue-shift in emission and enhances the intensity in the aggregate state. Among them, NA12C is most likely to form micelles and the most obvious fluorescence enhancement, which will switch over time due to the nano-aggregation transition.

Effects of donor and acceptor substituents on the photophysics of 4-ethynyl-2,1,3-benzothiadiazole derivatives.

The present work explores the photophysical, electrochemical, and fluorescence polarization properties of a group of π-conjugated phenylethynyl-2,1,3-benzothiadiazole derivatives (BTDs) bearing different electron-donating (ED) or electron-withdrawing (EW) substituents at the para position of the phenylethynyl moiety. The BTDs were synthesized through the Sonogashira cross-coupling reaction between 4-bromo-2,1,3-benzothiadiazole and the respective para-substituted phenylethynyl derivatives. The BTDs with the EW-substituents show relatively weak solvatochromic behavior, while the BTDs with the strong ED-substituents like methoxy and N,N-dimethylamino-based substituents (BTDPhOMe and BTDPhNMe2) exhibit a pronounced solvatochromic behavior. The change in dipole moments in the excited states of the derivatives was calculated using Lippert-Mataga plots. The conclusions drawn on the spectral behavior of the molecules could be rationalized by TD-DFT calculations involving electron density difference (EDD) maps that correlate with the ICT characteristics of the molecules. The experimental and theoretical calculations reveal that the BTDs with the strong ED-substituents (strong push-pull type BTDs) have a strong ICT character in the excited state. These strong push-pull type BTDs show high fluorescence quantum yield (ΦF) in apolar solvents and low ΦF in polar solvents. In contrast, the BTDs with the weak ED-substituents (weak push-pull type BTDs) and EW-substituents (pull-pull type BTDs) have a weaker ICT character with low ΦF in apolar and high ΦF in polar solvent media. There is good a agreement among the HOMO-LUMO band gaps obtained from absorption spectroscopy and electrochemical studies and theoretical calculations. The fluorescence anisotropy measurement in the glycerol medium shows that the studied BTDs generally exhibit higher sensitivity towards microviscosity than the traditional DPH fluorescence anisotropy probe.

Modification of optical properties in helicenes via construction of phosphine oxide-based push-pull systems

Six [6]helicene based push-pull systems combining three diarylamines as donors and two phosphine-oxides as acceptors were designed and synthesized in order to modify optical properties of the helicene skeleton. The properties of the target compounds were studied by DFT calculations and spectroscopic methods in both solution and solid film and compared to those of purposely synthesized reference compounds. It was found that the optical properties change substantially upon formation of the push-pull system and show dependence on the withdrawing ability of the acceptor. Furthermore, the introduction of the diphenylaminophenylene group as a donor led to significant increase of fluorescence quantum yield and also a significant dependence of the fluorescence maxima on the polarity of solvent – solvatochromism. The Lippert-Mataga plots were used to estimate the change in dipole moments (Δμ).

Tuning hybridized local and charge transfer emission in pyrene derivatives by incorporating phenanthroimidazole to realize high exciton harvest in blue organic light-emitting diodes

Pyrene derivatives capable of harvesting triplet excitons and displaying blue electroluminescence are limited. A new series of pyrene-based blue-emitting hybridized local and charge transfer materials is designed by asymmetrically substituting at the 1,3-positions of pyrene with phenanthroimidazole and N-phenylcarbazole. Electronic excitations due to pyrene localized and the charge transfer from phenanthroimidazole to pyrene segments dominate the absorption of the dyes. Incorporation of carbazole enhanced the charge transfer characteristics in the compounds and lead to the hybridization of local and charge transfer states. Theoretical studies revealed the possibility of exciton harvesting via the high lying triplet states, which have matching energy with the first excited singlet state. Lippert-Mataga plots for the solvatochromic data of the dyes exhibited bilinear relationship attributable to the formation of local state in the non-polar solvents and charge transfer state in the polar solvents. All the derivatives served as emitting layers in doped as well as non-doped multilayered organic light-emitting devices and exhibited deep-blue electroluminescence. The doped devices displayed much higher EL performance on comparing with that of the non-doped devices due to the proper alignment of energy levels leading to efficient exciton harvesting. The device containing carbazole derivative as dopant with tris(4-carbazoyl-9-ylphenyl)amine host displayed the highest external quantum efficiency of 8.4% with 50% exciton harvest.

Steric effects on the intramolecular charge transfer fluorescence of benzo[b]thiophene-1,1-dioxide bridged macrocages.

Intramolecular charge transfer (ICT) fluorescence has been widely investigated and exploited in sensor molecules. However, steric effects on the ICT fluorescence properties have rarely been reported so far, although research in this area would promote an understanding of the basics of solvation. Herein, we report the detailed fluorescence properties of bis(trimethylsilyl)benzo[b]thiophene-1,1-dioxide (TMSBTO2) and its caged cyclophanes and non-cage isomers, which demonstrate ICT fluorescence in various solutions. The fluorescence band maxima for these benzo[b]thiophene-1,1-dioxides (BTO2s) showed a red-shift with increasing solvent polarity, confirming ICT fluorescence characteristics. The linearity of the Lippert-Mataga plots was confirmed for all ICT fluorescence measured in hexane, toluene, AcOEt, CH2Cl2, and EtOH. The slopes of the plots decreased in the following order: TMSBTO2, non-cage isomers, and caged BTO2s. It is concluded that the Onsager radii for these BTO2s were increased in the abovementioned order, assuming that the difference in the dipole moments between the excited and ground states for these BTO2s was identical.

Electron Push-Pull Effects on Intramolecular Charge Transfer in Perylene-Based Donor-Acceptor Compounds.

A series of asymmetric donor-acceptor (D-A) perylene-based compounds, 3-(N,N-bis(4'-(R)-phenyl)amino)perylene (Peri-DPA(R)), were successfully prepared to explore their intramolecular charge transfer (ICT) properties. To induce ICT between the donor and acceptor, diphenylamine (DPA) derivatives (electron donor units) with the same functional groups (R = CN, F, H, Me, or OMe) at both para positions were linked to the C-3 position of perylene to produce five Peri-DPA derivatives. A steady-state spectroscopy study on Peri-DPA(R)s exhibited a progressively regulated ICT trend consistent with the substituent effect as it progressed from the electron-withdrawing group to the electron-donating group. In particular, a comparative study using a D-A-D (donor-acceptor-donor) system demonstrated that not only the electron push-pull substituent effect but also subunit combinations influence photophysical and electrochemical properties. The different ICT characters observed in Lippert-Mataga plots of D-A(CN) and D-A-D(CN) (CN-substituted D-A and D-A-D) led to the investigation on whether ICT emission of two systems with differences in subunit combinations is of the same type or of a different type. The femtosecond transient absorption (fs-TA) spectroscopic results provided direct evidence of ICT origin and confirmed that D-A(CN) and D-A-D(CN) exhibited the same transition mix of ICT (from donor to acceptor) and reverse ICT (rICT, from arylamine to CN unit). Density functional theory (DFT)/TD-DFT calculations support the presence of ICT for all five compounds, and the experimental observations of rICT presented only for CN-substituted compounds.

Base Promoted Synthesis of 2-((5-methoxynaphthalen-1-yl)methyl)-3-methyl-5-sec-amino-[1,1′-biphenyl]-4-carbonitrilederivatives: Photophysical, Solvatochromic and DFT studies

Newer, simple and efficient synthesis of 2-((5-methoxynaphthalen-1-yl)methyl)-3-methyl-5-sec-amino-[1,1′-biphenyl]-4-carbonitrile derivatives using ring transformation strategy. The synthesized products were characterized by spectral analysis, fluorescence emission and absorption measurements were studied in various solvents having varying polarity and dielectric constants to find out a change in dipole moment in ground state and excited state of derivatives. Lippert–Mataga plots were utilized to know the effect of solvent polarity on spectral behavior of molecules. The position of the Stokes shifts was found to be depends on specific solute–solvent interactions, playing a vital role in electronic excitation of molecules. A rational relationship is examined between fluorescence quantum efficiencies and calculated HOMO and LUMO energies by DFT calculations. The electrochemical investigation of derivatives was performed by cyclic voltammetry.

Fluorescent dyes for moisture detection in organic solvents: Push-pull based phenothiazine aldehydes with large Stokes shifts

In an effort to develop probes for efficient detection of traces of water, a series of push-pull based donor (D)-acceptor (A) phenothiazine aldehydes displaying large Stokes shifts (115−156 nm) was designed and synthesized. Several aryl groups with hydrogen bonding ability were appended on the phenothiazine ring with an aim of enhancing moisture sensitivity and surrounding solvent environment dependency. The solvatochromic studies and Lippert-Mataga plots indicated the presence of positive solvatochromism in all the compounds. The maximum ICT character was displayed by compound in which phenothiazine ring was appended with 4-formylphenyl ring. The possibility of twisted intramolecular charge transfer (TICT) states in this compound was revealed by Rettig plot. The regression analysis of Kamlet-Taft equations and the values of their correlation coefficients indicated that solvatochromic effect was influenced by solvent polarity and hydrogen bonding interactions. Among common organic solvents, water detection by all the compounds was found to be most sensitive in acetonitrile with detection limits 0.003−0.006 v/v %, suggesting their potential as low-cost moisture detecting probes for industrial applications.

Synthesis, photophysical properties, and density functional theory studies of phenothiazine festooned vinylcyclohexenyl-malononitrile.

A novel phenothiazine derivative conjugated with vinylcyclohexenyl-malononitrile (PTZ-CDN) was synthesized through the Knoevenagel reaction of 10-octyl-10H-phenothiazine-3,7-dicarbaldehyde with 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)-malononitrile and fully characterized. The UV-vis absorption spectra of PTZ-CDN in different solvents showed a λmax band at 497-531 nm with a high molar extinction coefficient attributed to intramolecular charge transfer (ICT) with the characteristics of a π-π* transition. Increasing the solvent polarity resulted in a bathochromic shift of λmax . The PTZ-CDN fluorescence emission spectra were more sensitive to increasing the solvent polarity than the absorption spectra; they displayed a blue shift of λem by 85 nm. To understand the behaviour of the PTZ-CDN derivative, Stokes' shift ( with respect to the solvent polarity, Lippert-Mataga and linear solvation-energy relationship (LSER) models were applied in which the LSER showed better regression than the Lippert-Mataga plots (r2 = 0.9627). Finally, the TD-density functional theory (DFT) electronic transition spectra in dioxane and dimethyl formamide (DMF) were calculated. The DFT data showed that λmax resulted from the support of the highest occupied molecular orbital to the lowest unoccupied molecular orbital transition with 74% and 99% in dioxane and DMF, respectively.

Deep Red emitting dicyanovinylene isophorone based chromophores: Combined synthesis, optical properties, viscosity sensitivity, and DFT studies

Deep red emitting dicyanovinylene isophorone based dyes are synthesized and studied for photophysical properties, viscosity sensitivity, and DFT. The dyes consist of Carbazole and Triphenylamine donor and thiophene spacer together with one auxiliary accepter, –CN leads to deep red emission towards the NIR region (∼600−700 nm) in polar solvent media. All dyes show good emission solvatochromism with an increase in solvent polarity. The dyes show intramolecular (ICT) as well as “Twisted Intramolecular Charge Transfer (TICT)” which is reinforced by Lippert Mataga, MacRae, Weller, and Rettig plots. Viscosity induced emission enhancement study in ethanol/polyethylene glycol (PEG 400) system shows 4.34–4.85 folds increases emission intensity. ICT is supported by Frontier Molecular Orbital (FMO) diagram and bandgap energy. The observed experimental findings are also correlated with the computed values using “Density Functional Theory (DFT)”. The magnitudes of “first order hyperpolarizability”(β0) are 500−1000 × 10−30.e.s.u. while those of the “second order hyperpolarizability”(γ) are 3000−8300 × 10-36 e.s.u. Hence they can act as very good NLOphores. Mulliken Hush analysis and Natural Bond Orbital (NBO) analysis were used to support charge transfer characteristics.

Systematic Control of Structural and Photophysical Properties of π-Extended Mono- and Bis-BODIPY Derivatives.

A series of π-extended mono- and bis-BODIPY (BODIPY=boron-dipyrromethene) derivatives, namely, benzo[a]phenanthrene-fused BODIPY (Phena-Mono-BDP), benzo[a]anthracene-fused BODIPY (Ant-Mono-BDP), and dibenz[a,h]anthracene (DBA)-bridged bis-BODIPY (Ant-Bis-BDP), were designed and synthesized to examine their structural, electrochemical, and photophysical properties. Single-crystal X-ray crystallographic analyses demonstrated the planar configuration of Ant-Mono-BDP, in contrast to that of nonplanar Phena-Mono-BDP, whereas Ant-Bis-BDP has a DBA-centered planar configuration and two terminal nonplanar units of BODIPYs. The oxidation and reduction potentials agree with the estimated energies obtained through DFT calculations. The localized HOMO and LUMO states suggested the intramolecular charge-transfer characteristics in these BODIPY derivatives. The absorption spectra of these compounds extended up to the near-IR region. Strong redshifted trends of fluorescence spectra were observed in Ant-Bis-BDP with increasing solvent polarity, as supported by the differences in dipole moments estimated from Lippert-Mataga plots. To evaluate the excited-state dynamics of these molecules, the fluorescence quantum yield (ΦFL ) of Ant-Bis-BDP dramatically increased in the range from 0.05 to 0.86, with decreasing solvent polarity. Finally, the efficient two-photon absorption cross section of Ant-Bis-BDP (ca. 1200 GM at λ=1000 nm) was also obtained by considering the large π-extended structure (acceptor-donor-acceptor type).

Electron Push-Pull Effects in 3,9-Bis(p-(R)-diphenylamino)perylene and Constraint on Emission Color Tuning.

A series of perylene-based donor-acceptor-donor (D-A-D) compounds, 3,9-bis(p-(R)-diphenylamino)perylene (R: CN (2a), F (2b), H (2c), Me (2d), and OMe (2e)), was synthesized using 3,9-dibromoperylene with p-(R)-diphenylamine, and the intramolecular charge transfer (ICT) on the D-A-D system with regard to the electron push-pull substituent effect was investigated. By introducing various p-(R)-diphenylamine derivatives with electron-donating or electron-withdrawing R groups, the energy band gaps of the D-A-D compounds were systematically controlled and the emission colors were efficiently tuned from green to red. As expected, the steady state emission spectra of all D-A-D compounds were observed, as well as the emission color controlled, depending on the Hammett substituent constants (σp). In the Lippert-Mataga plots, a different charge-transfer character was observed depending on the electron push-pull substitution, which showed gradually increased ICT characters from the electron-withdrawing to donating substitution. However, exceptionally, the strong electron-withdrawing group of CN-substituted 2a did not correlate with the other R group compounds. From the experimental data and density functional theory calculations, we assume that there is a constraint on emission color tuning to generate higher energy of blue emission in the D-A-D molecular system, due to the reverse charge-transfer property caused by the strong electron-withdrawing group.

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D-π-)2A fluorescent dyes.

The donor–acceptor–π-conjugated (D–π–)2A fluorescent dyes OUY-2, OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as D (electron-donating group)–π (π-conjugated bridge) moiety and a pyridine, pyrazine or triazine ring as electron-withdrawing group (electron-accepting group, A) have been designed and synthesized. The photophysical and electrochemical properties of the three dyes were investigated by photoabsorption and fluorescence spectroscopy, Lippert–Mataga plots, cyclic voltammetry and density functional theory calculations. The photoabsorption maximum (λmax,abs) and the fluorescence maximum (λmax,fl) for the intramolecular charge-transfer characteristic band of the (D–π–)2A fluorescent dyes show bathochromic shifts in the order of OUY-2 < OUK-2 < OUJ-2. Moreover, the photoabsorption bands of the (D–π–)2A fluorescent dyes are nearly independent of solvent polarity, while the fluorescence bands showed bathochromic shifts with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert–Mataga plots for OUY-2, OUK-2 and OUJ-2 indicate that the Δμ (= μe − μg) value, which is the difference in the dipole moment of the dye between the excited (μe) and the ground (μg) states, increases in the order of OUY-2 < OUK-2 < OUJ-2. Therefore, the fact explains our findings that OUJ-2 shows large bathochromic shifts of the fluorescence maxima in polar solvents, as well as the Stokes shift values of OUJ-2 in polar solvents are much larger than those in nonpolar solvents. The cyclic voltammetry of OUY-2, OUK-2 and OUJ-2 demonstrated that there is little difference in the HOMO energy level among the three dyes, but the LUMO energy levels decrease in the order of OUY-2 > OUK-2 > OUJ-2. Consequently, this work reveals that for the (D–π–)2A fluorescent dyes OUY-2, OUK-2 and OUJ-2 the bathochromic shifts of λmax,abs and λmax,fl and the lowering of the LUMO energy level are dependent on the electron-withdrawing ability of the azine ring, which increases in the order of OUY-2 < OUK-2 < OUJ-2.

Synthesis and Electrochemical and Photophysical Properties of Azaterrylene Derivatives.

A series of terrylene derivatives, such as monoazaterrylene (MATerry), 1,6-diazaterrylene (DiATerry) and pristine terrylene (Terry), were synthesized by changing the number of nitrogen atoms at the bay region (1 and 6 positions of the Terry core). The electrochemical measurements suggested that the first one-electron reduction and oxidation potentials became positively shifted with increasing numbers of nitrogen atoms. This agreed with the energies of the corresponding highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states estimated by DFT methods. In contrast, the HOMO-LUMO gaps approximately remained constant. This trend is quite similar to the spectroscopic behaviors observed by absorption and fluorescence spectra. The solvent polarity-dependent spectroscopic trends of DiATerry suggested the intramolecular charge-transfer (ICT) characters. The evaluation of the excited-state dynamics in various solvents indicated the electronic configurational changes of the excited states relative to the ground state via the ICT. This was supported by the Lippert-Mataga plots. Finally, the reversible protonation and deprotonation processes were also observed.

Blue and green light emitting polyarylpyrazolines luminogens containing anthracene and thiophene units

Polyarylpyrazolines are synthesized by Claisen-Schmidt condensation followed by Suzuki cross-coupling polycondensation. Polyarylpyrazolines (PAPF, PTPF) containing various aryl substituents emit with blue and green light makes them suitable for optoelectronics applications. Photophysical and electrochemical properties are changed by varying monomeric units in the polymer backbone. The polymers are designed to serve as difunctional charge carriers useful as both hole and electron transport materials in PLEDs and achieved by modulating the energy levels through changing segments and their emissive nature turn them as tri-functional polymers. The photophysical properties such as absorption and emission along with lifetime analysis were studied. The polymers are soluble in many organic solvents, hence solvatochromism explored and explained in nonpolar to polar solvents along with Lippert-Mataga plots. It is observed that LUMO level is brought down and imparts improved electron injection and better transport ability. One of fascinating characteristics of these polymers is trouble-free synthetic procedure, nontoxic and tuning emission properties. This approach yields a toolbox of molecules to construct π-conjugated polymers to explore better organic light emitting diode performance.

NLOphoric multichromophoric auxiliary methoxy aided triphenylamine D-π-A chromophores – Spectroscopic and computational studies

Molecules containing methoxy supported triphenylamine as strong electron-donor and dicyanovinyl as electron-acceptor groups interacting via isophorone as a configurationally locked polyene π-conjugated bridge are studied for their nonlinear optical properties. The photophysical study of examined chromophores in non-polar and polar solvents suggest that they exhibit strong emission solvatochromism and significant charge transfer characteristics supported by Lippert-Mataga plots and Generalised Mulliken Hush analysis. Linear and nonlinear optical properties as well as electronic properties measured by spectroscopic methods and cyclic voltametry and supported by DFT calculation were used to elucidate the structure property relationships. All three chromophores exhibit very high thermal stabilities with the decomposition temperatures higher than 340°C. The vibrational motions play very important role in determining the overall NLO response styryl chromophores which was established by DFT study. Dye 3 with maximum nonlinear optical susceptibility among three D-π-A systems proves that the multibranched push-pull chromophores exhibit a higher third order nonlinear susceptibility and justifies the design strategy.

Synthesis and optical and electrochemical properties of julolidine-structured pyrido[3,4-b]indole dye.

The julolidine-structured pyrido[3,4-b]indole dye ET-1 has been newly designed and developed as a small D-A fluorescent dye. ET-1 showed bathochromic shifts of the fluorescence band upon changing from aprotic solvents to protic solvents, as well as positive fluorescence solvatochromism. Moreover, it was found that ET-1 can form a 1 : 1 Py(N)-B complex with boron trifluoride and a hydrogen-bonded proton transfer (Py(N)-H) complex with trifluoroacetic acid, which exhibit photoabsorption and fluorescence bands at a longer wavelength region than the pristine ET-1. Based on optical (photoabsorption and fluorescence spectroscopy) and electrochemical (cyclic voltammetry) measurements, Lippert-Mataga plots, 1H NMR spectral measurement and density functional theory (DFT) calculation, this work indicated that the Py(N)-B complex or the Py(N)-H complex is effectively formed and stable in solution. This is due to the strong Py(N)-B interaction or Py(N)-hydrogen-bond, which can be attributed to the enhanced basicity or the accumulated electron density on the nitrogen atom of the pyridine ring caused by the introduction of a julolidine (quinolizidine) moiety as a strong electron-donating group. We propose that the D-A-type dye ET-1 based on the julolidine-structured pyrido[3,4-b]indole possesses the ability to act as a calorimetric and fluorescent sensor for Brønsted and Lewis acids.

Multi-Stimuli Responsive Donor–Acceptor Tetraphenylethylene Substituted Benzothiadiazoles

In order to understand how the donor (D)/acceptor (A) substituents and their substitution pattern affect the solution and solid-state optical properties, a series of symmetrical and unsymmetrical TPE substituted BTDs 3–8 were designed and synthesized by the Suzuki and Stille coupling reactions. Their solvatochromic, aggregation induced emission (AIE), mechanochromic, and vapochromic properties were studied and compared. The single-crystal X-ray structures of BTDs 5 and 6 are reported. The BTDs 3–8 are highly fluorescent with the tunable emissions. The solvent dependent emission was observed in BTDs 3–8 and their Lippert–Mataga plots show a linear correlation of the Stokes shift with solvent polarity. The emission study in different tetrahydrofuran (THF):water percentages show enhanced emission in aggregates. The BTDs exhibit a reversible multi-stimuli response toward mechanical force, solvent, and heat. The detailed study using single-crystal X-ray, photophysical properties, powder X-ray diffraction, scan...

Synthesis and properties of bipolar derivatives of 1,3,5-triazine and carbazole

Three new bipolar star-shaped derivatives of 2,4,6-triphenyl-1,3,5-triazine containing carbazolyl groups were designed, synthesized and characterized. All the materials possess high thermal stability and high glass transition temperatures ranging 97–226 °C. Photophysical study of the dilute solutions and neat films of the synthesized compounds was performed. Lippert–Mataga plots revealed linear dependence of Stokes shifts on the orientation polarizability for all the compounds. The dilute solutions of the triazine derivatives exhibited high photoluminescence quantum yields reaching 0.85, while for the neat films photoluminescence efficiency of 0.20–0.33 was observed. Ionization potentials of the solid layers of carbazole-triazine adducts estimated by photoelectron spectroscopy were found to be in the range of 5.49–5.97 eV. Hole drift mobility of the materials well exceeded the magnitude of 10−3 cm2 V−1 s−1 at an electric field of 6.4 · 105 V/cm. The selected compounds were tested as light emitting materials in organic light emitting diodes based on host-guest systems.

5-N-Arylaminothiazoles as Highly Twisted Fluorescent Monocyclic Heterocycles: Synthesis and Characterization.

A series of 5-N-arylaminothiazoles was prepared by reacting thioamide dianions derived from secondary thioamides with thioformamides, followed by sequential oxidation with iodine. X-ray analyses demonstrated that they adopt structures that are highly twisted from planar conformations. Their orientations were tuned by the steric and/or electronic interactions of the substituents at their 2-, 4-, and 5-positions. The 5-aminothiazoles exhibited a range of fluorescent emissions, from blue to orange. Although the absorption spectra were independent of the polarity of the solvent, fluorescent emissions were influenced by the polarity of the solvent: in more polar solvents, the emissions were red-shifted. These phenomena were examined in terms of Lippert-Mataga plots and the change in the dipole moment between the ground and excited states. They also exhibited emissions in the solid state, again from blue to orange. Cyclic voltammetry of the 5-aminothiazoles showed reversible waves of one-electron oxidation. The half-potential of the oxidation was reduced by the introduction of electron-donating groups to the phenyl groups on the nitrogen atom at the 5-position. DFT calculations were carried out to determine the energy levels of the HOMO and LUMO. Finally, the results of TG-DTA showed that they are thermally stable.