Nm In Toluene Research Articles

Anthracene-based blue fluorescence materials utilized in non-doped OLEDs with high luminance and a low efficiency roll-off

In this work, we designed and synthesized two novel blue-emitting compounds (m-TAC and p-TAC) with a twisted D-π-A configuration by incorporation of 2,4,6-triphenyl-1,3,5-triazine as an acceptor and carbazole as a donor through an anthracene π-spacer. Therein, p-TAC exhibits a hybridized local and charge-transfer (HLCT) characteristic with a sky-blue emission at 462 nm in toluene while m-TAC shows emission maximum at 431 nm. The two compounds exhibit superb thermal stability in the company of a thermal decomposition temperature (Td) as high as 507 and 516 °C. It is noticed that the non-doped devices with m-TAC and p-TAC as blue emitters display a turn-on voltage (Von) of 3.2 V and achieve sky-blue emission at 460 and 476 nm. In particular, the optimized device based on p-TAC realizes a maximum luminance above 10 000 cd m−2 and the maximum external quantum efficiency (EQEmax) reaching 5.03%. As a sky-blue HLCT emitter, p-TAC reveals high-efficiency electroluminescence (EL) performance, providing a new insight for further industrial applications.

The selective regulation of borylation site based on one-shot electrophilic C–H borylation reaction, achieving highly efficient narrowband organic light-emitting diodes

The electrophilic borylation site of borylation reaction can be selectively controlled by varying the steric hindrance and electron-donating ability of the substrate substituent. The device based on the synthesized compound exhibits EQE of 21.6% with FWHM of 28 nm and CIE coordinates of (0.135, 0.094). The work provides an effective way for the development of high-performance MR-TADF emitter. • The electrophilic borylation site of one-shot electrophilic C–H borylation reaction can be selectively controlled. • New compounds tDPAC-BN and tDMAC-BN exhibited high PLQYs, narrow FWHMs, and satisfactory TADF properties. • The device based on tDPAC-BN achieved EQE of 21.6% with FWHM of 28 nm and CIE coordinates of (0.135, 0.094). Developing novel thermally activated delayed fluorescence (TADF) materials with a small full-width at half-maximum (FWHM) is very important for the fabrication of wide gamut and high-resolution displays of organic light-emitting diodes (OLEDs). In this work, we report two blue TADF emitters (tDPAC-BN and tDMAC-BN) with narrow FWHM based on a one-shot electrophilic C–H borylation reaction by selecting acridan-containing arylamine derivatives as the starting materials of borylation. The rigid skeleton structure significantly reduces vibrational motion, endowing tDPAC-BN and tDMAC-BN with high PLQYs (94.4% and 89.7%) and narrow FWHMs (19 nm and 26 nm in toluene). The electroluminescent devices employing tDPAC-BN and tDMAC-BN as emitters exhibit external quantum efficiency (EQE) of 21.6% and 22.3%, and CIE coordinates of (0.135, 0.094) and (0.116, 0.186), respectively. More importantly, we found the electrophilic borylation site of borylation reaction can be controlled by varying the steric hindrance effect and electron-donating ability of the substrate substituent. The different HOMO distribution originated from the differences in the substrate substituent accounts for different cyclization mode for tDPAC-BN and tDMAC-BN. Therefore, the work provides a useful strategy for broadening the range of high-performance TADF materials with narrow FWHM.

Near-Infrared fluorescent unsymmetrical aza-BODIPYs: Synthesis, photophysics and TD-DFT calculations

In view of the ever-growing demand for efficient NIR fluorophores for biomedical applications, we herein report the synthesis and properties of four unsymmetrical aza-BODIPYs exhibiting NIR fluorescence. Highly desirable photophysical and photochemical properties were induced in these molecules due to the presence of both strongly electron-withdrawing p-nitrophenyl rings (p-NO2Ph-) and mildly electron-donating p-methoxyphenyl rings (p-MeOPh-) within the aza-BODIPY core. In particular, upon excitation with λabs the unsymmetrical aza-BODIPYs studied exhibited NIR emission with λf ranging from 699 nm to 718 nm in toluene. The fluorescence quantum yields (Φf), depending on the substitution pattern, ranged from Φf = 0.49 to Φf = 0.22 and the fluorescence lifetimes ranged from τf = 1.90 ns to τf = 3.59 ns. Aza-BODIPY with electron-donating substituent at 3 position and electron-withdrawing substituent at 5 position was identified as cell permeable, NIR emitting fluorophore suitable for bioimaging.

Absorption and Fluorescence Properties of 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione. A Covalent Fluorescence in Solution and in the Solid State

In the cuurent article, the photophysical properties of 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione were investigated. The visible absorption bands at 527, 558 and 362 nm in propylene carbonate and the compound was found to be fluorescent in solution and in the plastic film with emission wavelengths between 550- 750 nm. The Stokes Shift of P.C., acetonitrile, diethyl ether, Tetrahydrofuran THF, cyclohexane, dibutyl ether, and dichloromethane DCM are 734, 836, 668, 601, 601, 719, and 804 cm-1 in respectively. The Stokes Shift Δ was less in THF and cyclohexane, than the solvents, which indicates that the energy loss is less between the excitation and fluorescence states. The photophysical characterizations were carried out on the compound in different solvents, the compound displays 12 nm red-shift in the absorption maximum in toluene compared with in propylene carbonate P.C, which the λmax was 558 nm in P.C. The compound displays 5 and 10 red-shifts in the absorption maximum in diethyl ether and dibutyl ether respectively. The absorption band is almost insensitive to the polarity of the solvent, showing only a slight red shift from 563 nm in diethyl ether to 569 nm in cyclohexane and also red shift from 558 nm in acetonitrile to 570 nm in toluene , which appreciably red-shifted depending on the polarity of the solvent. The emission maxima of the dye slightly shift more red region, such as DCM and toluene when compared this compound in other solvents. The dye showed a slight red shift ca. 5 nm on moving from the acetonitrile to the less polar solvent, such as dichloromethane DCM.

Extremely low efficiency roll-off in vacuum- and solution-processed deep-red/near-infrared OLEDs based on 1,8-naphthalimide TADF emitters

Deep-red to near-infrared (DR-NIR) organic light-emitting diodes (OLEDs) based on purely organic thermally activated delayed fluorescence (TADF) emitters usually suffer from serious efficiency roll-offs. Herein, a series of 1,8-Naphthalimide-derivatives-based wedge-shape emitters, 2DN and 2PN, were designed and synthesized by adopting multiple donor units and isopropyl modification strategies. 2DN and 2PN exhibited strong DR-NIR TADF in the range 646–755 nm in toluene and films. The OLEDs, fabricated by both vacuum-deposition and solution-processed methods, all exhibited desired DR-NIR electroluminescence in the range 629–701 nm, and significantly reduced efficiency roll-offs (8.4% for 2DN and near zero for 2PN at 100 cd m−2), which benefit from short delayed lifetime (36.4 us for 2DN and 14.0 us for 2PN) and negligible π-π stacking in aggregation states. It indicates that the efficiency roll-offs of DR-NIR TADF OLEDs can be greatly reduced by designing emitters with appropriate design of molecular structures.

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Intramolecular charge transfer-induced solvatochromism and large Stokes shifts of furocoumarins

A series of furocoumarins (4a-h) was synthesized via a multi-component reaction and characterized by FTIR, 1H NMR, 13C NMR and ESI-MS. Compound 4g was further characterized with single-crystal X-ray diffraction for the molecular packing and interaction analysis. The photophysical and photochemical properties of the series have been experimentally and theoretically investigated, focusing on the absorption and fluorescence properties in solvents of varying polarity. Geometry optimization, HOMO-LUMO energy gap, NBO analyses and potential nonlinear optical (NLO) responses for all furocoumarins (4a-h) have been computed using DFT/TD-DFT method. The experimental results reveal that absorption and fluorescence of furocoumarins are highly sensitive to the solvent polarity and inter or intramolecular interactions. Furocoumarin exhibits strong solvatochromism through the intramolecular charge transfer (ICT) process, large Stokes shift up to 142 nm in polar solvents, long emission wavelength up to 520 nm in polar protic solvent through large polarization and relative high quantum efficiencies up to 94% in DMSO. Compound 4h exhibits Stokes shift value of 197 nm in toluene. The charge transfer character was correlated with the Lippert-Mataga and McRae plots while the effect of substituents on the fluorescence quantum yield was described by the Hammett plot. Based on the theoretical computations, furocoumarins with strong electron donating substituents (4b and 4d) possess high frequency-dependent first order hyperpolarizabilities, β in the range of 21.32–27.34 × 10−30 esu, suggesting their possible use in the NLO application. Fluorescence quenching in 4c, 4g and 4h were caused by site-specific hydrogen bonding strengthening and molecular packing that led to the formation of excimer species. This work will be valuable for the exploitation of ICT and solvatochromic effects and future molecular engineering of organic materials for practical utilities endowing low cost, facile and greener approach.

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Chiral Thermally Activated Delayed Fluorescence Materials Based on R/S‐N2,N2′‐Diphenyl‐[1,1′‐binaphthalene]‐2,2′‐diamine Donor with Narrow Emission Spectra for Highly Efficient Circularly Polarized Electroluminescence

AbstractIn this study, two pairs of chiral thermally activated delayed fluorescence (TADF) materials enabling circularly polarized luminescence (CPL) named R/S‐p‐BAMCN (rod‐shape) and R/S‐o‐BAMCN (helix‐shape) are prepared based on a new pair of chiral donor (D*), R/S‐N2,N2′‐diphenyl‐[1,1′‐binaphthalene]‐2,2′‐diamine (R/S‐BAM), and two cyano (CN) acceptors. Due to the rigid molecular structure and special intramolecular arrangement, the chiral TADF materials show high photoluminescence quantum efficiency (up to 0.86) with narrow full‐width at half‐maximum (38 nm in cyclohexane, 51 nm in toluene) and photoluminescence dissymmetry factor (|gPL|) up to 5.3 × 10−3. Particularly, the circularly polarized OLEDs (CP‐OLEDs) with rod‐shaped R/S‐p‐BAMCN as the emitter show high device performances with the maximum external quantum efficiency nearing 28%. Meanwhile, the semi‐transparent CP‐OLEDs based on helix‐shaped R/S‐o‐BAMCN exhibit obvious circularly polarized electroluminescence (CPEL) properties with the electroluminescence |gEL| factors around 4.6 × 10−3. The strategy of rigid D*‐A‐D* structure with special arrangement of chiral donor provides a direct way to obtain efficient CP‐TADF materials with narrow emission spectra and promising CPL properties for better CPEL performance.

Combined experimental and density functional theory studies on novel 9‐(4/3/2‐cyanophenyl)‐9H‐carbazole‐3‐carbonitrile compounds for organic electronics

AbstractWe have synthesized a series of novel hybrid molecules 9‐(2‐cyanophenyl)‐9H‐carbazole‐3‐carbonitrile (o‐CNCbzCN), 9‐(3‐cyanophenyl)‐9H‐carbazole‐3‐carbonitrile (m‐CNCbzCN) and 9‐(4‐cyanophenyl)‐9H‐carbazole‐3‐carbonitrile (p‐CNCbzCN), comprising electron‐donating carbazole and electron‐accepting nitrile groups. Three positional isomers were synthesized with a view to tune photophysical and electrochemical properties of the hybrids. The photophysical study displayed absorption maxima in the range of 281–340 nm and 277–298 nm whereas emission maxima in the range of 349–366 nm and 366–369 nm in toluene and dimethylformamide (DMF), respectively. These molecules demonstrated suitable frontier molecular orbital (FMO) energy levels and ensure good thermal and morphological stability. Among these synthesized molecules, m‐CNCbzCN showed very high decomposition temperature (Td = 341°C) whereas p‐CNCbzCN exhibited good glass transition (Tg = 182°C) as well as melting temperature (Tm = 236°C), indicating its significant stability and potential utility as a bipolar host material for efficient phosphorescent organic light‐emitting diodes (PhOLEDs).

A TADF Emitter Featuring Linearly Arranged Spiro-Donor and Spiro-Acceptor Groups: Efficient Nondoped and Doped Deep-Blue OLEDs with CIEy

Reported herein is a molecular design strategy of deep-blue emitters for resolving the lack of highly efficient deep-blue organic light-emitting diodes (OLEDs) featuring CIEy (Commission Internationale de l'Eclairage) color coordinates matching the display requirements (<0.1). The strategy is to combine weak spiro-donor and spiro-acceptor groups into a linear donor-π-acceptor type of thermally-activated delayed fluorescence molecule through a sterically bulky π-spacer. The strategy endows an emitter with deep-blue emission, a narrower emission bandwidth (51 nm in toluene), a high photoluminescence quantum yield (0.95 in toluene), weak concentration quenching, and efficient triplet-exciton utilization, which are all attractive characteristics for emitters of deep-blue OLEDs with lower CIEy coordinates. Owing to the rational design, the emitter has realized not only highly efficient doped deep-blue OLEDs with external quantum efficiencies (EQEs) up to 25.4 % and CIEy less than 0.1 but also so far the most efficient nondoped deep-blue OLED (EQE up to 22.5 %) with CIEy less than 0.1.

A TADF Emitter Featuring Linearly Arranged Spiro‐Donor and Spiro‐Acceptor Groups: Efficient Nondoped and Doped Deep‐Blue OLEDs with CIEy&lt;0.1

AbstractReported herein is a molecular design strategy of deep‐blue emitters for resolving the lack of highly efficient deep‐blue organic light‐emitting diodes (OLEDs) featuring CIEy(Commission Internationale de l'Eclairage) color coordinates matching the display requirements (&lt;0.1). The strategy is to combine weak spiro‐donor and spiro‐acceptor groups into a linear donor‐π‐acceptor type of thermally‐activated delayed fluorescence molecule through a sterically bulky π‐spacer. The strategy endows an emitter with deep‐blue emission, a narrower emission bandwidth (51 nm in toluene), a high photoluminescence quantum yield (0.95 in toluene), weak concentration quenching, and efficient triplet‐exciton utilization, which are all attractive characteristics for emitters of deep‐blue OLEDs with lower CIEycoordinates. Owing to the rational design, the emitter has realized not only highly efficient doped deep‐blue OLEDs with external quantum efficiencies (EQEs) up to 25.4 % and CIEyless than 0.1 but also so far the most efficient nondoped deep‐blue OLED (EQE up to 22.5 %) with CIEyless than 0.1.

Highly Efficient Near-Infrared Thermally Activated Delayed Fluorescence Molecules via Acceptor Tuning: Theoretical Molecular Design and Experimental Verification.

Near-infrared (NIR) thermally activated delayed fluorescence (TADF) materials have shown great application potential in organic light-emitting diodes, photovoltaics, sensors, and biomedicine. However, their fluorescence efficiency (ΦF) is still highly inferior to those of conventional NIR fluorescent dyes, seriously hindering their applications. This study aims to provide theoretical guidance and experimental verification for highly efficient NIR-TADF molecular design. First, the light-emitting mechanism of two deep-red TADF molecules is revealed using first-principles calculation and the thermal vibration correlation function (TVCF) method. Then several acceptors are theoretically designed by changing the position of the cyano group or by introducing the phenanthroline into CNBPz, and 44 molecules are designed and studied theoretically. The photophysical properties of DA-3 in toluene and the amorphous state are simulated using a multiscale method combined with the TVCF method. The NIR-TADF property for DA-3 is predicted both in toluene and in the amorphous state. Experimental measurement further confirms that the TADF emission wavelength of DA-3 is 730 nm and ΦF is as high as 20%. It is the highest fluorescence efficiency reported for TADF molecules with emission wavelengths larger than 700 nm in toluene. Our work provides an effective molecular design strategy, and a good candidate for highly efficient NIR-TADF emitters is also predicted.

Near-Infrared Boron Difluoride Formazanate Dyes.

Near-infrared (NIR) dyes are sought after for their utility in light harvesting, bioimaging, and light-mediated therapies. Since long-wavelength photoluminescence typically involves extensive π-conjugated systems of double bonds and aromatic rings, it is often assumed that NIR dyes have to be large molecules that require complex syntheses. We challenge this assumption by demonstrating that facile incorporation of tertiary amine groups into readily available 3-cyanoformazans affords efficient production of relatively simple NIR-active BF2 formazanate dyes (λabs =691-760 nm, λPL =834-904 nm in toluene). Cyclic voltammetry experiments on these compounds reveal multiple reversible redox waves linked to the interplay between the tertiary amine and BF2 formazanate moieties. Density-functional calculations indicate that the NIR electronic transitions in BF2 formazanates are of π→π*-type, but do not always involve strong charge transfer.

Solvent manipulation of the pre-reduction metal-ligand complex and particle-ligand binding for controlled synthesis of Pd nanoparticles.

Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. In this study, we show that the nucleation and growth rates are correlated with the thermodynamics of metal-ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability. The results show that the nucleation rate decreased, while the growth rate increased in the following order, toluene, piperidine, 3,4-lutidine and pyridine, leading to a large increase in the final nanoparticle size (from 1.4 nm in toluene to 5.0 nm in pyridine). Using density functional theory (DFT), complemented by 31P nuclear magnetic resonance and X-ray absorption spectroscopy, we calculated the reduction Gibbs free energies of the solvent-dependent dominant pre-reduction complex and the solvent-nanoparticle binding energy. The results indicate that lower nucleation rates originate from solvent coordination which stabilizes the pre-reduction complex and increases its reduction free energy. At the same time, DFT calculations suggest that the solvent coordination affects the effective capping of the surface where stronger binding solvents slow the nanoparticle growth by lowering the number of active sites (not already bound by trioctylphosphine). The findings represent a promising advancement towards understanding the microscopic connection between the metal-ligand thermodynamic interactions and the kinetics of nucleation and growth to control the size of colloidal metal nanoparticles.

Multi‐Color Emitting Pyrene Derivatives: Synthesis, Optoelectronic and Electroluminescent Properties

AbstractGiven the high fluorescence quantum yield and modifiability of pyrene, we designed, synthesized and characterized three novel pyrene derivatives (1‐‐3) bearing electron donors and/or acceptors. All of them exhibited strong emission bands at 470 nm, 527 nm, 606 nm in toluene and slightly red‐shifted bands in the solid state due to intermolecular interactions in the densely packed state. In addition, these compounds exhibited high thermal stability with decomposition temperatures of up to 372 °C for 1, 462 °C for 2 and 429 °C for 3. Fabrication of organic light emitting diodes with 1–3 as active layers were conducted, and the devices gave multi‐color fluorescence, including cyan, chartreuse and orange light with the CIE coordinates of (0.14, 0.35), (0.38, 0.59) and (0.58, 0.41), respectively.

Polyhedral oligomeric silsesquioxane cage integrated soluble and fluorescent poly(3,4-propylenedioxythiophene) dye

A new analog of poly (3,4-propylenedioxythiophene) conjugated polymers called PProDOT-POSS, where polyhedral oligomeric silsesquioxane (POSS) nanocage with alkyl substitutions was integrated on the bridge of 3,4-propylenedioxythiophene unit and its structure was confirmed by spectroscopic techniques, was reported. The polymers were synthesized via both chemical and electrochemical polymerization techniques. While chemical polymerization was carried out in the presence of anhydrous FeCl3 as an oxidant, a solution of 0.1 M tetrabutylammonium hexafluoride electrolyte dissolved in a mixture of dichloromethane and acetonitrile (1/3: v/v) was used as an electrolyte solution for electrochemical polymerization. Electro-optical properties of the corresponding polymers were characterized by using electroanalytical techniques such as cyclic voltammetry and square wave potentiometry, and spectrophotometric methods like ultraviolet–visible and fluorescent spectrophotometry. Corresponding polymers obtained both electrochemically and chemically are soluble completely in common organic solvents such as chloroform, toluene, dichloromethane, tetrahydrofuran, etc. Polymer samples both in film and solution forms can be doped/dedoped reversibly by using a chemical oxidant or an external potential. The optical bandgap of the neutral polymer film with a maximum absorption band at 555 nm was calculated as 1.95 eV. Polymers have fluorescent property and excited polymers represented a red/orange light with an emission band centered at 605 nm in toluene. Also, PProDOT-POSS polymers have electrochromic properties under external potentials and they have an optical contrast of 55% at 555 nm between their neutral and oxidized states. Upon oxidation, they showed high transparency and they can switch between redox states in a short time (switching time = ~1.0 s) as well as high coloration efficiency (502 cm2/C for 95% switching). It can be concluded that POSS based PProDOT polymers can be good candidates for optoelectronic and bioelectronics applications.Short Abstract for Paper Submission: A new analog of poly (3,4-propylenedioxythiophene) conjugated polymers called PProDOT-POSS, was reported with the integrated of alkyl-substituted polyhedral oligomeric silsesquioxane nanocage structure. The polymers were synthesized via both chemical and electrochemical polymerization techniques. Corresponding polymers obtained both electrochemically and chemically are soluble completely in common organic solvents such as chloroform, toluene, dichloromethane, tetrahydrofuran, etc. Polymer samples both in film and solution forms can be doped/dedoped reversibly by using a chemical oxidant or an external potential. The optical bandgap of the neutral polymer film with a maximum absorption band at 555 nm was calculated as 1.95 eV. Polymers have fluorescent property and excited polymers represented a red/orange light with an emission band centered at 605 nm in toluene.

1,8-Naphthalimide-Based Polymers Exhibiting Deep-Red Thermally Activated Delayed Fluorescence and Their Application in Ratiometric Temperature Sensing.

A series of naphthalimide (NAI)-based red-emissive thermally activated delayed fluorescence (TADF) acrylic monomers has been designed and synthesized. When copolymerized with a host material by Cu(0)-reversible deactivation radical polymerization (Cu(0)-RDRP), polymers exhibiting orange to deep-red TADF were obtained with quantum yields of up to 58% in solution and 31% in the solid state. These emitters exhibit dual emission consisting of high-energy prompt fluorescence from the NAI acceptor (λmax = 340 nm in toluene) and red-delayed fluorescence from the charge-transfer process (λmax = 633-711 nm in toluene). This dual emissive property was utilized to create red-to-blue temperature-responsive polymers by copolymerization of NAI-DMAC with N-isopropylacrylamide and a blue fluorescent dopant. These polymers exhibit red TADF at room temperature and blue fluorescence at 70 °C, with a high ratiometric fluorescent thermal response of 32 ± 4% K-1. Such systems are anticipated to have utility in bioimaging, drug delivery, and temperature sensing, further expanding the range of applications for red TADF materials.

Molecular‐Structure and Device‐Configuration Optimizations toward Highly Efficient Green Electroluminescence with Narrowband Emission and High Color Purity

AbstractThermally activated delayed fluorescence (TADF) materials that are able to realize electroluminescence showing simultaneously narrow emission band, high color purity, and high efficiency are highly demanded for display applications. Up to now, a few blue emissive TADF materials with such characteristics have been reported, while green TADF materials with such features are extremely scarce. Herein, two TADF compounds with highly efficient narrowband bluish green/green emission (full‐width at half‐maximum (FWHM): 22 and 21 nm in toluene) induced by multiple resonance effect are reported. An optimized organic light‐emitting diode based on the green emissive compound shows a fairly narrow electroluminescent spectrum (FWHM: 33 nm), as well as an excellent color purity with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.20, 0.65), which is a close resemblance to the standard green‐light CIE coordinates of (0.21, 0.71) defined by the National Television System Committee. Meanwhile, the maximum external quantum efficiency (EQE) up to 25.5% is achieved and a high EQE of 20.1% is maintained at a practical high luminance of 1000 cd m−2. The outstanding device performance of the compound makes it attractive for potential practical applications.

Building Molecular Complexity from Quinizarin: Conjoined Coumarins and Coronene Analogs.

The double Knoevenagel condensation of 1,4-dibenzoyloxyanthraquinone with methyl esters of arylacetic acids affords a series of compounds based upon a previously unknown 1,8-dioxa-benzo[e]pyrene-2,7-dione heterocyclic core. The aryl groups incorporated in the 3- and 6-positions can be oxidatively coupled to the π-expanded backbone to produce a further new heterocyclic core: 1,10-dioxa-dibenzo[dj]coronene-2,9-dione. The intriguing optical properties of these π-expanded coumarin derivatives are discussed and rationalized through quantum chemical calculations. The broad absorption bands of 1,8-dioxa-benzo[e]pyrene-2,7-dione-based dyes are attributed to both HOMO-1→LUMO and HOMO→LUMO transitions, which have a similar energy. Weakly coupled electron-donating aryl substituents result in a moderate bathochromic shift of both the absorption and emission by 30-60 nm in toluene. The emissive properties of these compounds are in part determined by the oscillator strength of the main transition, lifetimes of the excited state, and by the energy match of the excited state with a triplet state of a similar energy. The 1,10-dioxa-dibenzo[dj]coronene-2,9-dione displays a much smaller Stokes shift, yet a markedly increased fluorescence quantum yield of 90 % owing to the increased rigidity compared with the 1,8-dioxa-benzo[e]pyrene-2,7-dione core.