Syntheses and tunable emission properties of 2-alkynyl azulenes

Various substituted 2-azulenes have been synthesized via Sonogashira coupling. Doping with superacids allows tunable emission from 443 to 750 nm depending on the substitution. The proton doped compounds are the first azulene alkyne based systems that show emission originating only from the S(1) excited state.     

Theoretical Studies of Azulene and Its Derivatives

The results of ab initio calculation with STO-3G and 6-31G basis set on the azulene and its derivatives (included azulenequinones, diazoazulenequinones and polyether bridged azulenes) are presented in accordance with considerations of structures and bonding. Azulene is a nonalternant aromatic compound with ten π electrons and it has either C_s or symmetry dgpend on the different carbon and carbon bonding. The calculation results indicate that C_s symmetry is the ground state structure of azulene. TTie simple MO and CIS calculations describe the excited state of azulene.     

On the nature of excited electronic states in cyanine dyes: implications for visual pigment spectra

CNDO/S CI calculations are carried out on polyenes and on cyanine dyes. In contrast to polyenes, doubly excited configurations have a strong effect on the first optically allowed excited state in cyanines. Protonated Schiff bases of retinal are closely related to cyanine dyes, with important consequences for models of visual pigment spectra and photochemistry.     

Synthesis of 1‐(4‐thiazolyl)azulenes: Reactions of bromoacetyl‐substituted azulenes with thioamides,thioureas, and thiosemicarbazones

1‐(Bromoacetyl)‐3‐methylazulene (1a) and methyl 3‐(bromoacetyl)azulene‐1‐carboxylate (1b) reacted with thioamides 3a,b and thioureas 3c,d in boiling ethanol to give the corresponding (4‐thiazolyl)azulenes 4a‐d and 5a‐d in good yields, respectively. The reactions of dibromoacetyl‐substituted azulene (2) also gave (4‐thiazolyl) azulenes 5a‐d in lower yields and the azulene 2 was recovered. By heating compounds 5a‐d in 100% phosphoric acid, the ester group was eliminated to yield 1‐(4‐thiazolyl)azulenes 6a‐d. Compounds 1a,b reacted with thiosemicarbazones 7a‐f to afford [(2‐alkylidenehydrazino)thiazol‐4‐yl]azulenes 8a‐f and 9a‐f in moderate to high yields via their hydromides.     

Bischromophoric styrylpyridinium dyes. Spectroscopic properties of 1,3-bis-[4-(p-N,N-dialkylaminostyryl)pyridinyl]propane dibromides

The photophysical properties of newly synthesized bischromophoric solvatochromic stilbazolium dyes, 1,3-bis-[4-(p-N,N-dialkylaminostyryl)pyridinyl]propane dibromides (C1-C9), were studied in a series of solvents and their spectroscopic properties were compared with structurally related, monochromophoric styrylpyridinium dyes (SP1-SP9). The position of the UV-vis absorption spectra maximum of novel dyes is only slightly solvent polarity dependent in contrast to the fluorescence spectra that show pronounced solvatochromic effect demonstrated by a large Stokes shifts. The influence of the solvent on absorption and emission spectra, and the solvatochromic properties observed for both ground and first excited states for all the dyes were used for the evaluation of their excited state dipole moments. The ground state dipole moments of both mono- and bischromophoric dyes were established by applying ab initio calculations. The calculations and measurements unexpectedly show that the bischromophoric dyes are characterized by ground state dipole moments being equal to about half of that characterizing their monomeric equivalents, while the excited state dipole moments of bischromophoric dyes are about 10-25% higher in comparison to their monomeric equivalents.     

几种方酸菁染料的NMR及光谱特性研究

研究了几种方酸菁染料的核磁、可见、荧光光谱。通过二维核磁共振谱和¹³CNMR确定了分子的结构和构型。测定了其在不同溶剂中吸收光谱和荧光发射光谱及其发射的荧光量子产率。发现它具有微弱的正向溶致变色特性,通过光谱特征分析得出整个分子处于平面结构并形成一个长的共轭体系,其激发态和基态的结构相近的结论。同时,讨论了结构对分子电荷分布及相应荧光光谱特征的影响。     

Correlation of substituent effects and energy levels of the two lowest excited states of the azulenic chromophore

[structure: see text] Experimental and calculated data show that the relative energy levels of the two lowest excited states of azulene are sensitive to the nature and position of substituents on the nonalternant hydrocarbon. Extending such investigations led to a rational explanation for some of the baffling data on azulenic bacteriorhodopsin analogues in the literature.     

Role of heteroaromatic cycles in the inter- and intra-molecular dynamics of excited aryl ketones

Although the photophysics and photochemistry of aromatic carbonyl compounds have been extensively studied over several years, the interest in their photobehaviors is still alive and they continue to be investigated by exploiting advanced experimental and computational technologies. In this article complete series of pyridyl, di-pyridyl, thienyl, di-thienyl and thienyl-pyridyl ketones are reviewed, mainly from the spectroscopic and photochemical points of view. Properties and reactivity of their excited states have been investigated through stationary absorption and emission spectra, time resolved transient spectroscopy, dynamic luminescence techniques and computational methods. The results reported demonstrate that the photophysics and photochemistry of these molecules can be modulated by changing the rings linked to the carbonyl (pyridyl, thienyl, phenyl) and their linking position, as also the microenvironment where they are included. Of special importance are their properties of triplet photosensitizers and their ability in photogenerating free radicals. Enhancing or depressing such properties may be required in applications and this can be achieved by structure and environment changes.     

Photoreactions of aromatic compounds — XXVIII : Photo-induced reactions of 1-nitroazulene and derivatives with nucleophiles

The photosubstitutions of azulene, 1-nitroazulene and 3-substituted 1-nitroazulenes with nucleophiles have been investigated. In these azulenes the atom at position 1 proved to be the most reactive in accord with the calculated excited state charge densities. The photomethoxylation of 1-nitroazulene probably proceeds through a triplet state. The quantum efficiency of this reaction proved to be wavelength-dependent indicating that intersystem crossing from higher excited singlet states may occur.     

Porphyrin-perylene bisimide dyads and triads: synthesis and optical and coordination properties

[structure: see text] Novel porphyrin perylene dyad and triad dyes have been prepared by the coupling of aminophenyltrisphenylporphyrin and tetraphenoxy-substituted perylenetetracarboxylic acid bisanhydrides in a one-step synthesis. Fluorescence spectra of these compounds reveal features that are attributable to emission of perylene bisimides as well as porphyrin excited states. The self-assembly behavior of zinc-metalated compounds with 4,4'-bipyridine and diazabenzoperylene has been investigated by (1)H NMR spectroscopy in CDCl(3), showing that oligomeric zigzag assemblies are formed.     

Anomalous fluorescence spectra of 1-isopropylidene-1H-cyclopent[a]azulene and 3-isopropylidene-3H-cyclopent[a]azulene

The electronic and fluorescence spectra of 1-isopropylidene-1H-cyclopent[a]azulene and 3-isopropylidene-3H-cyclopent[a]azulene, which are iso-π-electron systems of benz[a]azulene, have been measured. Anomalous fluorescence spectra have been observed for both compounds. It has been concluded that these compounds emit fluorescence from the second excited singlet state.     

Strategic emission color tuning of highly fluorescent imidazole-based excited-state intramolecular proton transfer molecules

Highly fluorescent molecules harnessing the excited state intramolecular proton transfer (ESIPT) process are promising for a new generation of displays and light sources because they can offer very unique and novel optoelectronic properties which are different from those of conventional fluorescent dyes. To realize innovative ESIPT devices comprising full emission colors over the whole visible region, a molecular design strategy for predictable emission color tuning should be established. Here, we have developed a general strategy for a wide-range spectral tuning of imidazole-based ESIPT materials based on three different strategies--introduction of a nodal plane model, extension of effective conjugation length, and modification of heterocyclic rings. A series of nine ESIPT molecules were designed, synthesized and comprehensively investigated for their characteristic emission properties. All these molecules commonly showed no clear and transparent visible range absorption with no absorption color, but showed different colors of intense photoluminescence over broad visible regions from 450 nm (HPI) to 630 nm (HPNO) depending on their molecular structure. With the aid of density functional theory and time-dependent DFT calculations using M06, wB97XD, and B3LYP parameters with the 6-31G(d,p) basis set, these tuned emission bands of nine emitters were assigned from the stabilized excited state conformations that were derived from modified molecular structures.     

Solution processable indoloquinoxaline derivatives containing bulky polyaromatic hydrocarbons: synthesis, optical spectra, and electroluminescence

New hybrid materials featuring the dipolar fragment 6H-indolo[2,3-b]quinoxaline attached to the bulkier polyaromatic hydrocarbons such as fluoranthene, triphenylene, or polyphenylated benzene have been synthesized by a two-step procedure involving Sonogashira and Diels-Alder reactions. They were characterized by absorption, emission, electrochemical, thermal, and theoretical investigations. The electronic properties of the compounds were dominated by the 6H-indolo[2,3-b]quinoxaline chromophore, and the incorporation of polyaromatic hydrocarbons reduces the chances of nonradiative deactivation processes associated with the excited state and improves the emission properties. The compounds displayed cyan emission with moderate quantum efficiency when excited at the absorption maximum. All of the compounds exhibited an irreversible reduction process corresponding to the addition of electron at the quinoxaline segment. They showed moderate thermal stability and glass transition temperature greater than 100 °C. The presence of rigid 6H-indolo[2,3-b]quinoxaline and bulkier polyaromatic hydrocarbon segments enhances the thermal stability and glass transition temperature significantly. Finally, the dyes were successfully applied as an electron-transporting and emitting layer in multilayered organic light-emitting diodes comprising a N,N'-bis(l-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine hole-transporting layer. The cyan emitting devices were characterized by moderate device performance parameters.     

Theoretical approach to the out-of-plane deformation of 1,3-disubstituted azulenes

Computational calculations at B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels were employed to analyze the structure and conformation of 1,3-bis(4-bromophenyl)azulene (1), 1,3-bis(2-thienyl)azulene (2), and 1,3-bis(2-pyrrollyl)azulene (3) in order to rationalize the out-of-plane deformation found in the azulene cores of 1 and 2 in the crystalline state, whereas compound 3 shows a totally planar azulene moiety. Our results indicate that 1,3-disubstituted azulenes possess two almost equally stable and easily convertible minimum energy conformers, which differ in the relative orientation of the substituent groups and in the planarity degree of the azulene core. An absolute planarity index (P) is introduced to quantify the out-of-plane distortion found in the azulenes under study. The aromaticity of minimum energy conformers was evaluated by means of geometric (HOMA), magnetic (NICS), and energetic (the frequency of the lowest out-of-plane vibration, ν_min) aromaticity indicators, which suggest that compound 3 possesses the most aromatic azulene core within the group. Calculated molecular dipole moments suggest that the conformation of 1,3-disubstituted azulenes in the crystalline state can be explained in terms of electrostatic intermolecular interactions rather than relative stability of planar and non-planar conformers.     

Azulene‐1‐azo‐2′‐thiazoles. Synthesis and properties

Several derivatives belonging to a new compound class, namely azulene‐1‐azo‐2′‐thiazoles, were prepared by the diazotization of 2‐aminothiazoles in the presence of HNO₃/H₃PO₄ followed by the coupling of diazonium salts with azulenes in buffered medium. The reactions proved to be general for this class, the yields are, however, considerably influenced by the substituents at thiazole moiety. For the first time a N‐oxide provided from an amino substituted five‐member nitrogenous heterocycle was diazotized and coupled. The structure of the obtained compounds was assigned and their physico‐chemical properties were discussed. The new azulene azo derivatives exhibit a strong bathochromic shift in UV‐Vis due to the intense push‐pull effect of aromatic system and to the intrinsic properties of thiazole moiety.     

Influence of solvent and substituent on excited state characteristics of laser grade coumarin dyes

Absorption and fluorescence emission of 4 and 7 substituted coumarins viz. C 440, C 490, C 485 and C 311 have been studied in various polar and non-polar organic solvents. These coumarin dyes are substituted with alkyl, amine and fluorine groups at 4- and 7-positions. They give different absorption and emission spectra in different solvents. The study leads to a possible assignment of energy level scheme for such coumarins including the effect on ground state and excited state dipole moments due to substitutions. Excited state dipole moments of these dyes are calculated by solvetochromic data experimentally and theoretically these are calculated by PM 3 method. The dipole moments in excited state, for all molecules investigated here, are higher than the corresponding values in the ground state. The increase in dipole moment has been explained in terms of the nature of excited state and resonance structure.     

Generation and characterization of highly vibrationally excited molecular beam

A simple method to generate and characterize a pure highly vibrationally excited azulene molecular beam is demonstrated. Azulene molecules initially excited to the S4 state by 266-nm UV photons reach high vibrationally excited levels of the ground electronic state upon rapid internal conversion from the S4 electronically excited state. VUV laser beams at 157 and 118 nm, respectively, are used to characterize the relative concentrations of the highly vibrationally excited azulene and the rotationally and vibrationally cooled azulene in the molecular beam. With a laser intensity of 34 mJ/cm2, 75% of azulene molecules absorb a single 266-nm photon and become highly vibrationally excited molecules. The remaining ground-state azulene molecules absorb two or more UV photons, ending up either as molecular cations, which are repelled out of the beam by an electric field, or as dissociation fragments, which veer off the molecular-beam axis. No azulene without absorption of UV photons is left in the molecular beam. The molecular beam that contains only highly vibrationally excited molecules and carrier gas is useful in various experiments related to the studies of highly vibrationally excited molecules.     

A class of nonplanar conjugated compounds with aggregation-induced emission: structural and optical properties of 2,5-diphenyl-1,4-distyrylbenzene derivatives with all cis double bonds

We have studied the structural and optical properties of four 2,5-diphenyl-1,4-distyrylbenzene derivatives with all cis double bonds. These compounds belong to a class of nonplanar conjugated compounds possessing a typical Aggregation-Induced Emission (AIE) property that has no emission in solution but intense emission in crystal. The four molecules are packed in different stacking modes with different intermolecular interactions, resulting in different crystalline state photoluminescence (PL) efficiency. The torsional molecular configuration increases the intermolecular distances effectively in the crystalline state, which decreases the difference of the optical properties from the frozen isolated molecules to the crystalline state. The Stokes shifts of these compounds are very large and the PL spectra have only one broad emission band with poor structure, due to the relatively large configuration difference between the ground state and the first singlet excited state, and the abundant vibration energy levels of the torsional molecule with changeable conformation.     

Electronic spectroscopy and photoisomerization of trans-urocanic acid in a supersonic jet.

trans-Urocanic acid (trans-UA), a component of the epidermal layer of skin, exhibits wavelength-dependent photochemistry. The quantum efficiency of isomerization to cis-UA is greatest when the molecule is excited on the long wavelength tail of its absorption profile in solution (300-320 nm). However, exciting the molecule where it absorbs UV light most efficiently (260-285 nm) causes almost no isomerization. We have used fluorescence excitation and dispersed emission methods in a supersonic jet to investigate the electronic states involved in this complex and interesting photochemistry. Three distinct regions are present in the excitation spectrum. Region I, which is below the isomerization barrier, contains sharp, well-resolved peaks that upon excitation emit from the S(1) state of trans-UA. Region II exhibits peaks that increase in broadness and decrease in intensity with increasing excitation energy. Upon excitation these peaks produce dual emission from the S(1) states of both trans- and cis-UA. The trans to cis isomerization barrier is estimated to be 1400 cm(-1). Region III exhibits excitation to the S(2) electronic state and has a broad structure that spans 3000 cm(-1) and occurs 4000 cm(-1) above S(1). S(2) excitation results in essentially no trans to cis isomerization.     

Database of Absorption and Fluorescence Spectra of >300 Common Compounds for use in PhotochemCAD

The design of new molecules for photochemical studies typically requires knowledge of spectral features of pertinent chromophores beginning with the absorption spectrum (λ _abs) and accompanying molar absorption coefficient (ε , m ⁻¹ cm⁻¹) and often extending to the fluorescence spectrum (λ _em) and fluorescence quantum yield (Φ_f), where the fluorescence properties may be of direct relevance or useful as proxies to gain insight into the nature of the first excited singlet state. PhotochemCAD databases, developed over a period of 30 years, are described here. The previous databases for 150 compounds have been expanded to encompass 339 compounds for which absorption spectra (including ε values), fluorescence spectra (including Φ_f values) and references to the primary literature have been included where available (552 spectra altogether). The compounds exhibit spectra in the ultraviolet, visible and/or near‐infrared spectral regions. The compound classes and number of members include acridines (21), aromatic hydrocarbons (41), arylmethane dyes (11), azo dyes (18), biomolecules (18), chlorins/bacteriochlorins (16), coumarins (14), cyanine dyes (19), dipyrrins (7), heterocycles (26), miscellaneous dyes (13), oligophenylenes (13), oligopyrroles (6), perylenes (5), phthalocyanines (11), polycyclic aromatic hydrocarbons (16), polyenes/polyynes (10), porphyrins (34), quinones (24) and xanthenes (15). A database of 31 solar spectra also is included.