Fluorescence Quantum Yield In Solution Research Articles

Remarkable solution and solid-state color-tunable luminescence of diethylamino-coumarin derivatives and application in warm-white LEDs

Organic materials with solution and solid dual efficient, color-tunable luminescence are potentially useful for sensors and optical devices. Herein, a series of donor-π-acceptor luminophores, named BMs, with different phenyl substituents at the 3-positions of 7-diethylamino-coumarin was developed. All four compounds with slightly twisted structure rendering BMs have bright emission in solution and solid state. BMs not only possess solvatochromic properties in solution but also realize color tuning from cyan (480 nm) to deep red (661 nm) in solid states. Among them, the fluorescence quantum yield of compound BM1 in solid state reached 98.2%, and the fluorescence quantum yield in solution was 77.1%. Time dependent density functional theory calculation and single crystal analysis show that with the increase in the electron-withdrawing ability of 4-phenyl moiety at the 3-position of coumarin, the charge transfer effect was strengthened gradually, and the photoluminescence mechanism changed from intramolecular charge transfer (ICT) to twisted ICT on account of the electron acceptor changed accordingly. Moreover, the cyan phosphor BM1 and the deep-red phosphor BM4 were laminated to fabricate an impressive warm-white light-emitting diode device with a maximum brightness of 52,090 cd/m2 at an operating voltage of 4.0 V.

Synthesis, photophysics, and theoretical calculations of styryl-based fluorophores harboring substituted benzothiazole acceptors

This study describes the synthesis, photophysical characterization, and TD-DFT calculation of a series of benzothiazole-based styryl fluorophores (F1-F5) harboring a D-π-A structure. The compounds were obtained through a simple and efficient synthetic route using low-cost starting materials. The investigation and analysis of their photophysical properties enable the assessment of the effect of four substituted benzothiazole moieties (A) and two types of π-conjugated frameworks (phenyl vs thienyl) in solution and in solid state. The fluorophores disclose absorption in the ultraviolet-blue region with a moderate solvatochromic effect and a single emission band located at the blue-green spectral range. In the solid state, the fluorophores showed emission in the green-orange regions with a relatively large Stokes shift. The systematic UV–vis solvatochromism study and theoretical predictions using the CPCM model reveals the increment in the dipole moment of the systems in an excited state with the solvent dielectric constant. These compounds showed high fluorescence quantum yield in solution and in solid-state and could be further exploited for solid-state lighting devices, or embedded in the design of biological dyes.

Assembling of Perylene, Naphthalene, and Pyromellitic Diimide-Based Materials and Their Third-Order Nonlinear Optical Properties

π-conjugated aromatic diimides with chemical stability, heat resistance, and redox activity have attracted more attention due to their excellent fluorescence quantum yield in solution. The planar perylene diimide (PDI) derivatives generally have aggregation-induced emission quenching in the solid state, while the cyclic trimers based on pyromellitic diimides (PMDIs), naphthalene diimides (NDIs), and PDIs can increase the fluorescence quantum yield in the solid state and have large two-photon absorption cross section, which can be used as excellent nonlinear optical (NLO) materials. Therefore, this paper will study the effects of multiple assembly modes of the three monomers on the NLO responses of materials. It was found that the assembly modes of 2PMDI-1NDI and 2NDI-1PDI exhibit larger third-order NLO response (γ) values, which was due to the larger conjugate surface of PDI effectively reducing the energy gap between the HOMO and LUMO. Compared with other assembly methods, 2PMDI-1NDI and 2NDI-1PDI were conducive to causing redshifts (150 nm) in the absorption spectrum. Therefore, the larger conjugate surface of PDI and the assembly mode of the isosceles triangle were more favorable for intramolecular charge transfer, thus improving its NLO properties.

A highly efficient solution and solid state ESIPT fluorophore and its OLED application

Readily accessible and functionalized ESIPT dyes with high fluorescence quantum yield in solution, including water, and in crystalline state are presented.

Between Aromatic and Quinoid Structure: A Symmetrical UV to Vis/NIR Benzothiadiazole Redox Switch.

Reversibly switching the light absorption of organic molecules by redox processes is of interest for applications in sensors, light harvesting, smart materials, and medical diagnostics. This work presents a symmetrical benzothiadiazole (BTD) derivative with a high fluorescence quantum yield in solution and in the crystalline state and shows by spectroelectrochemical analysis that reversible switching of UV absorption in the neutral state, to broadband Vis/NIR absorption in the 1st oxidized state, to sharp band Vis absorption in the 2nd oxidized state, is possible. For the one‐electron oxidized species, formation of a delocalized radical is confirmed by electron paramagnetic resonance spectroelectrochemistry. Furthermore, our results reveal an increasing quinoidal distortion upon the 1st and 2nd oxidation, which can be used as the leitmotif for the development of BTD based redox switches.

Ultrafast spectroscopy of biliverdin dimethyl ester in solution: pathways of excited-state depopulation.

Biliverdin is a bile pigment that has a very low fluorescence quantum yield in solution, but serves as a chromophore in far-red fluorescent proteins being developed for bio-imaging. In this work, excited-state dynamics of biliverdin dimethyl ether (BVE) in solvents were investigated using femtosecond (fs) and picosecond (ps) time-resolved absorption and fluorescence spectroscopy. This study is the first fs timescale investigation of BVE in solvents, and therefore revealed numerous dynamics that were not resolved in previous, 200 ps time resolution measurements. Viscosity- and isotope-dependent experiments were performed to identify the contributions of isomerization and proton transfer to the excited-state dynamics. In aprotic solvents, a ∼2 ps non-radiative decay accounts for 95% of the excited-state population loss. In addition, a minor ∼30 ps emissive decay pathway is likely associated with an incomplete isomerization process around the C15[double bond, length as m-dash]C16 double bond that results in a flip of the D-ring. In protic solvents, the dynamics are more complex due to hydrogen bond interactions between solute and solvent. In this case, the ∼2 ps decay pathway is a minor channel (15%), whereas ∼70% of the excited-state population decays through an 800 fs emissive pathway. The ∼30 ps timescale associated with isomerization is also observed in protic solvents. The most significant difference in protic solvents is the presence of a >300 ps timescale in which BVE can decay through an emissive state, in parallel with excited-state proton transfer to the solvent. Interestingly, a small fraction of a luminous species, which we designate lumin-BVE (LBVE), is present in protic solvents.

Ethynyl‐Tolyl Extended 2‐(2′‐Hydroxyphenyl)benzoxazole Dyes: Solution and Solid‐state Excited‐State Intramolecular Proton Transfer (ESIPT) Emitters

Dual solution/solid‐state emissive fluorophores based on a 2‐(2′‐Hydroxyphenyl)benzoxazole (HBO) core bearing one or two ethynyl‐tolyl moieties at different positions were synthesized via an expedite two‐step synthetic procedure. HBO derivatives are known to display intense Excited‐State Intramolecular Proton Transfer (ESIPT) emission in the solid‐state but are mildly emissive in solution due to the detrimental flexibility of the excited‐state opening efficient non‐radiative pathways. The sole introduction of a rigid ethynyl moiety led to a sizeable enhancement of the fluorescence quantum yield in solution, up to a 15‐fold increase in toluene as compared to unsubstituted HBO dyes while keeping the high solid‐state fluorescence efficiency. The position of the substitution on the π‐conjugated core led to subtle fine‐tuning of maximum emission wavelengths and quantum yields. Moreover, we show that the ethynyl tolyl substituent at the para position of the phenol ring is a suitable moiety for an efficient stabilization of the corresponding emissive anionic HBO derivatives in dissociative solvents like DMF THF or EtOH. These observations were confirmed in CH3CN by a basic titration. For all dyes, the nature of the excited‐state involved in the fluorescence emission was rationalized using ab initio calculations.

Tetraazatetraoxodecacene and tetraazatetrathiodecacene: Synthesis, crystal structures, linear and third-order nonlinear optical properties

In this manuscript, the longest O/N and S/N atoms containing heteroacenes (tetraazatetraoxodecacene (TAOD) and tetraazatetrathiodecacene (TATD)) with ten linearly fused rings have been synthesized and fully characterized. The X-ray crystal structures show that O/N atoms containing TAOD exhibits a linear structure, while S/N atoms containing TATD bends in S atom containing heterorings. Obviously, TAOD shows a higher fluorescence quantum yield in solution than that of S atom containing compound TATD. By simple reprecipitation method, TAOD and TATD self-assembly into different microstructures with microwires and microrods, respectively, which demonstrate distinctive non-linear optical properties depending on the orientation of transition dipoles.

Synthesis and characterization of 9,10-[di-p-(7-diethylamino- coumarin-3-yl) thiopheneyl]anthracene as fluorescent material

ABSTRACTA novel N-coumarin derivative, namely 9,10-[di-p-(7-diethylamino-coumarin-3-yl) thiopheneyl]anthracene ((CTh)2A), containing anthracene as the core and 3-thiophene N-coumarin as the substituent was synthesized, and its structure was confirmed by 1H NMR and IR spectroscopies. The optical, electrochemical and thermal properties were investigated. Thermogravimetric analysis and PL spectra reveal the high thermal and good photoluminescence characteristics. The coumarin derivative exhibits blue photoluminescence with high fluorescence quantum yield in solution (up to 40%). The results show that the derivative would serve as promising organic light-emitting diode luminescent material.

Insights into the effect of donor-acceptor strength modulation on physical properties of phenoxazine-based imine dyes

Novel phenoxazine-based imine dyes having a donor-acceptor-donor (D-A-D) topology were designed, synthesized and thoroughly investigated with regard to their thermotropic, photo-physical and electrochemical behaviour. The hexyl-substituted phenoxazine was selected as donor moiety and diphenyl-1,3,4-oxadiazole or fluorene-containing moieties were employed as electron-acceptor groups, being connected via the imine bond. The supramolecular architecture from solution and in molten state has been investigated by wide angle X-ray diffraction, differential scanning calorimetry and polarized light microscopy. The imines formed distinctive thermotropic mesophases in close relationship with their structure. The molecular rigid rods of the synthesized dyes formed supramolecular layered structures that further combine into worm-like anisotropic primary particles in the condensed phase with a strong impact on the physical properties of the dyes. UV–Vis absorption, photoluminescence, and electrochemical measurements proved the ability of the imine bond to facilitate the intramolecular charge-transfer transition from the donor to the acceptor units. The dyes showed an inverted solvatochromic behaviour, the fluorescence emission being highly sensitive to solvent polarity, yielding blue to green and even orange light in different organic solvents. A change in the relative intensity of the photoluminescence with the excitation wavelength of those phenoxazine-based imine dyes has been detected. The fluorescence quantum yield in solution reached up to 63%, whilst in film state it significantly dropped. By incorporating segments with different electron-accepting capability, the HOMO–LUMO energy gap was modulated from 1.88 to 1.92 eV. The electrochemical features demonstrate that p- and n-type doping to the conducting state of these phenoxazine-based imine materials is achievable. As a consequence of interesting physical properties encountered in these dyes, applications in optoelectronic devices are foreseen.

Synthesis of a Tyr-Tyr Peptide Library and Fluorescence of the Stilbenyl Derivatives

An expeditious ultrasound–assisted synthesis of a tyrosine–tyrosine peptide library is presented. Dipeptide synthesis and functionalization, via Suzuki-Miyaura or Sonogashira cross-coupling reactions, was carried out and led to sixteen extended conjugation derivatives in moderate to good yields. Both o-hydroxy- and o-methoxy-trans-stilbenyl-Tyr-Tyr peptides emit blue fluorescence when irradiated with ultraviolet light. The fluorescence quantum yield of solutions of these peptides in methanol, acetonitrile or THF was 0.20 ± 0.05. Quantum chemical calculations at the Time-Dependent Density Functional Theory (TDDFT) level suggests that, for both peptides, emission originates from the stilbene core.

Synthesis and Properties of Substituted Polyacetylenes Containing Pyrene Moieties in the Side Group

Abstract A novel phenylacetylene derivative containing a pyrene group was synthesized and polymerized with various Rh complex catalysts. The obtained polymers were soluble in common organic solvents such as chloroform and THF. The Mw and Mw/Mn were estimated as ca. 12000–18000 and 1.3–1.7 respectively, and the polymer yields were estimated as around 57–72%. The characteristic absorptions of ≡C–H (3200 cm−1) and C≡C (2100 cm−1) stretchings seen in the monomer spectra have completely disappeared in the polymer spectra from IR spectrum. 1H NMR analysis confirmed that the acetylene triple bonds transformed to polyene double bonds. These polymers were found to be thermally stable based on TGA data. The synthesized polymers exhibited blue fluorescence. The fluorescence quantum yield in solution was high at 0.37–0.41. Furthermore, the obtained polymer had a long fluorescence lifetime.

Reactive bay functionalized perylene monoimide-polyhedral oligomeric silsesquioxane organic electronic dye

Abstract Aggregation-induced quenching is particularly detrimental in perylene diimides, which are characterized by a near-unity fluorescence quantum yield in solution but are far less emissive in the solid state. Previously, perylene diimide has been improved by linking it to the inorganic cage of polyhedral oligomeric silsesquioxanes. As a further study on perylene diimidepolyhedral oligomeric silsesquioxanes, we report on a double functionalized molecular structure, which can be used for substitution at the bay area and as a side group in other materials. Typical solution absorption and emission features of the perylene diimide fragment have been observed in this new reactive perylene diimide-polyhedral oligomeric silsesquioxane. Moreover, reduced stacking during aggregation and spherical particles exhibiting solid fluorescence have been obtained. Organic semiconducting material with enhanced solid state photophysical properties, like solid fluorescence is a subject of great interest owing to its possible high-tech applications in optoelectronic devices.

Synthesis, crystal structure and photochromism of new diarylethenes with a benzene moiety

Three unsymmetrical diarylethenes with both thiophene and benzene moieties were synthesized. Their crystal structures and photochromic features were investigated systematically to elucidate the substituent effects of the terminal phenyl group on photochromism. Computational studies were performed to provide further insight into their frontier molecular orbitals and spatial distributions of electronic density. Each compound exhibited favorable photochromism in hexane and functioned as notable fluorescent photo-switches with fluorescence quenching efficiency of ∼96% induced by the intensity change of UV/vis light. Among the three diarylethenes, the cyano group on the terminal phenyl group significantly decreased the distance of the two reactive carbon atoms and strengthened the intermolecular hydrogen bond stacking interactions, resulting in improved stability in crystal state. Furthermore, it exhibited a red-shifted absorption maximum, an enhanced molar absorption coefficient, cyclization quantum yield, and fluorescence quantum yield in solution.

Synthesis and characterization of carbazole dendronized coumarin derivatives as solution-processed non-doped emitters and hole-transporters for electroluminescent devices

A series of carbazole dendronized coumarin derivatives (CTmGn, m = 0–2, n = 1–3) containing oligothiophenyl coumarins as cores and carbazole dendrons up to the third generation as substituents were synthesized and characterized. Their optical, thermal, electrochemical, and electroluminescent properties as non-doped solution-processed light-emitters and hole-transporters for OLEDs were investigated. They exhibited a bright light blue to yellow fluorescence with solution fluorescence quantum yields (ΦF) of about 0.10–0.40 and morphologically stable amorphous thin films with glass transition temperatures as high as 285 °C. As emissive layers, solution-processed OLEDs with the structure of ITO/PEDOT:PSS/CTmGn/BCP/LiF:Al emitted light blue to yellow colours with a maximum luminance efficiency as high as 7.92 cd A−1 and a low turn-on voltage of 3.6 V. As hole-transporting layers, solution-processed OLEDs with the structure of ITO/PEDOT:PSS/CGn/Alq3/LiF:Al showed a bright green emission (λEL = 518 nm, CIE = 0.27, 0.53) with a maximum luminance efficiency as high as 6.54 cd A−1 and a low turn-on voltage of 2.5 V.

Bifunctional oligofluorene-cored carbazole dendrimers as solution-processed blue emitters and hole transporters for electroluminescent devices

A series of bifunctional oligofluorene-cored carbazole dendrimers (GnFm, n = 1–3, m = 2–3) containing carbazole dendrons up to the third generation as end-caps were synthesized and characterized as non-doped solution-processed blue-light emitters and hole transporters for organic light-emitting diodes (OLEDs). Their optical, thermal, electrochemical, and electroluminescence properties were investigated. They exhibited a strong deep-blue fluorescence with solution fluorescence quantum yields (ΦF) of around 0.91–0.99 and formed morphologically stable amorphous thin films with glass transition temperatures as high as 273 °C. As blue emitters, solution-processed OLEDs with structure of ITO/PEDOT:PSS/GnFm/BCP/LiF:Al displayed a deep-blue emission (λELem = 415 nm, CIE = 0.17, 0.11) with a maximum luminance efficiency as high as 3.79 cd A−1 and a low turn-on voltage of 4.2 V. As hole transporters, solution-processed OLEDs with structure of ITO/PEDOT:PSS/GnFm/Alq3/LiF:Al showed a bright green emission (λELem = 520 nm, CIE = 0.30, 0.54) with a maximum luminance efficiency as high as 5.63 cd A−1 and a low turn-on voltage of 2.4 V.

New organic–inorganic hybrid materials based on perylene diimide–polyhedral oligomeric silsesquioxane dyes with reduced quenching of the emission in the solid state

Abstract Solid state luminescent materials are the subject of ever growing interest both from a scientific and a technological point of view because high-tech applications of light emitting materials very often require their use in the condensed phase. Aggregation caused quenching processes however represent an obstacle to the development of most luminogens in the condensed phase. This is why particularly fascinating are those materials showing high emission intensity in the solid state. Aggregation caused quenching is particularly detrimental for π-extended polycyclic aromatic hydrocarbons, for example perylene tetracarboxylic acid diimides which are characterized by a near-unity fluorescence quantum yield in solution but are far less emissive in the solid state. Here we report on the easy preparation and on the optical investigation of perylene tetracarboxylic acid diimide derivatives linked to the inorganic cage of polyhedral oligomeric silsesquioxanes. These new hybrid perylene diimide–polyhedral oligomeric silsesquioxane dyes show in solution the typical absorption and emission features of the perylene diimide fragment, with a quantum efficiency close to unity. Moreover, in the solid state (both as spin-coated films and powders) the electronic absorption spectra indicate a reduced fluorophore aggregation and significant quantum yield efficiencies induced by the positive effect of the polyhedral oligomeric silsesquioxane cage.

Nature of the influence of a solvent on the fluorescence quantum yield of solutions of the fluorescent probe 4-dimethylaminochalcone

The fluorescence quantum yields of solutions of 4-dimethylaminochalcone (DMC) in a series of individual solvents of different chemical nature have been measured using a technique based on studying the kinetics of fluorescence decay. A new quantitative regularity, namely, the dependence of the fluorescence quantum yield on the absolute solvation shift in the fluorescence spectrum due to the gas-solution phase transition, has been revealed. The opinion has been advanced and justified that the revealed regularity has a fundamental character, which is determined by the dominant contribution from the universal intermolecular interactions to the formation of the properties of the solvated DMC molecule in the excited electronic state.

Spectral-luminsecent properties of polyalkanesteramides

Absorption and fluorescence spectra and fluorescence quantum yields of solutions and transparent films of polyalkanesterimides (PAEI) were studied. The molecular chain of the investigated polyalkanesterimides contains phthalimide repeating units and –(CH2)n– fragments where n = 6 and 10. It is shown that the fluorescent properties of such polymers are the same as those of low-molecular-weight phthalimide luminophores. The alkane fragments contained in the polymer chain have been concluded to prohibit a charge-transfer transition and thereby enhance the polyalkanesterimide fluorescence intensity.

Porphyrin, Phthalocyanine and Porphyrazine Derivatives with Multifluorenyl Substituents as Efficient Deep‐Red Emitters

The synthesis and photophysical properties are described for a series of porphyrin, phthalocyanine and pyrazinoporphyrazine derivatives which bear four or eight peripheral fluorenyl substituents as antennae. Representative examples are 5,10,15,20-tetra(9,9-dihexyl-9H-fluoren-2-yl)porphyrin (2), 5,10,15,20-tetrakis[4-(9,9-dihexyl-9H-fluoren-2-yl)phenyl]porphyrin (3), 2,3,9,10,16,17,23,24-octakis(9,9-dihexyl-9H-fluoren-2-yl)-29H,31H-phthalocyanine (8) and 2,3,9,10,16,17,23,24-octakis[4-(9,9-dihexyl-9H-fluoren-2-yl)phenyl]-29H,31H-tetrapyrazinoporphyrazine (9). Palladium-mediated Suzuki-Miyaura cross-coupling reactions have been key steps for attaching the substituents. The compounds are deep-red emitters: lambda(max)(em)=659 (3), 737 (8) and 684 nm (9). Their absorption and emission spectra, their fluorescence lifetimes and quantum yields are correlated with the structures of the macrocycles and the substituents. The solution fluorescence quantum yields of porphyrin derivatives substituted with fluorene (2-4) and terphenyl substituents (7) (Phi(f)=0.21-0.23) are approximately twice that of tetraphenylporphyrin. For phthalocyanine derivative 8, Phi(f) was very high (0.88). Specific excitation of the fluorene units of 8 produced emission from both of them (lambda(max)=480 nm) and also from the phthalocyanine core (lambda(max)=750 nm), indicating a competitive rate of energy transfer and radiative decay of the fluorenes. Organic light-emitting devices (OLEDs) were made by spin-coating techniques by using a polyspirobifluorene (PSBF) copolymer as the host blended with 3 (5 wt. %) in the configuration ITO/PEDOT:PSS/PSBF copolymer:3/Ca/Al. Deep-red emission (lambda(max)=663 nm; CIE coordinates x=0.70, y=0.27) was observed with an external quantum efficiency of 2.5 % (photons/electron) (at 7.5 mA cm(-2)), a low turn-on voltage and high emission intensity (luminance) of 5500 cd m(-2) (at 250 mA/ m(2)).