Theoretical study on structural, electronic, and optical properties of ambipolar diphenylamino end-capped oligofluorenylthiophenes and fluoroarene-thiophene as light-emitting materials

Ambipolar diphenylamino end-capped oligofluorenylthiophenes and fluoroarene-thiophene show great potential for application in organic light-emitting diodes (OLEDs). Here, we provide an in-depth investigation on the optical and electronic properties of OF(2)TP-NPh ( 1a), OF(2)DTP-NPh ( 2a), OF(2)TTP-NPh ( 3a), OF(2)QTP-NPh ( 4a), and 2,5-bis-(2,3,5,6-tetrafluoro-4-trifluoromethyl-phenyl)-2,2':5',2':5',2'-quaterthiophene ( 5a). The geometric and electronic structures of the oligomers in the ground-state are studied with density functional theory (DFT) and ab initio Hartree-Fock, whereas the lowest singlet excited states are optimized by ab initio CIS. The energies of the lowest singlet excited states are calculated by employing time-dependent density functional theory (TDDFT). The results show that the highest occupied molecular orbitals, lowest unoccupied molecular orbitals, energy gaps, ionization potentials, and electron affinities for the oligomers are affected by the thiophene chain length and the different end-caps. The absorption and emission spectra exhibit red shifts to some extent due to the increasing thiophene chain length and the enhancing electron-donating property of the end-caps. Furthermore, the large Stokes shifts ranging from 58 to 80 nm are examined, resulting from a more planar conformation of the excited-state between the two adjacent units in the oligomers. All the calculated data show that the fluoroarene-thiophene has improved electron transport rate and charge transfer balance performance, and all the studied molecules can be used as ambipolar-transporting materials in OLEDs.     

Theoretical Studies on the Electronic and Optical Properties of a New Class of Aromatic Oligomers and Polymers

The purpose of this work is to provide an in‐depth interpretation of the optical and electronic properties of a series of aromatic oligomers and polymers, including [N‐(4‐(5‐(3‐(1,3,4‐oxadiazol‐2,5‐ylene)phenyl)‐1,3,4‐oxadiazol‐2‐ylene)phenyl)‐N‐(1,4‐phenylene)amine]_n (NPPP)_n and [N‐(4‐(5‐(3‐(1,3,4‐oxadiazol‐2,5‐ylene)phenyl)‐1,3,4‐oxa‐diazol‐2‐ylene)phenyl)‐N‐(1,4‐phenylene)naphthalene‐1‐amine]_n (NPPN)_n (n=1–4). These polymers and oligomers show great potential for application to organic light‐emitting diodes (OLEDs) as efficient blue emitters due to the tuning of the optical and electronic properties. The geometric and electronic structures of the oligomers in the ground state were investigated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited state of NPPP₁ was optimized with ab initio configuration interaction singles (CIS). To assign the absorption and emission peaks observed in the experiment, the absorption and emission spectra of the ground and lowest singlet excited states were calculated with time‐dependent DFT (TD‐DFT) and Zerner's independent neglect of differential overlap (ZINDO). All DFT calculations were performed using the B3LYP functional and the 6‐31G basis set. The results show that the HOMO, LUMO, energy gaps, ionization potentials, and electron affinities for these polymers are affected by increasing the conjugated chain, which favors the hole and electron injection into OLED. The trend of the variation of Δ_H‐L and the lowest excitation energies with 1/n, and the electronic structure and optical properties of these polymers were extrapolated and analyzed. The absorption spectra exhibit red shifts to some extent [the absorption spectra: 359.47 (NPPP₁)<370.84 (NPPP₂)<373.84 (NPPP₃)<375.33 nm (NPPP₄); 361.14 (NPPN₁)<370.34 (NPPN₂)<373.39 (NPPN₃)<374.62 nm (NPPN₄)]. Our calculated spectra agree well with the experimental findings where available, showing small but systematic deviations.     

Star-shaped Organic Molecules That Comprise a 1,3,5-Trisubs-tituted Benzene Core and Three Oligoaryleneethynylene Arms as Light-emitting Materials

Star‐shaped rigid molecules that comprise a 1,3,5‐trisubstitued benzene core and three oligoaryleneethynylene arms have great potential application in organic light‐emitting devices (OLEDs). Their optical and electronic properties are tuned by the star‐shaped molecular size. To reveal the relationship between the properties and structures, we perform a systemic investigation for these organic molecules. The ground and excited state molecules are studied using density functional theory (DFT), the ab initio HF, and the single excitation configuration interaction (CIS), respectively. And the electronic absorption and emission spectra are investigated with time‐dependent density functional theory (TDDFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods. The results show that the HOMOs, LUMOs, energy gaps, ionization potentials (IP), electron affinities (EA), absorption and emission spectra are controlled by the star‐shaped molecular size, which favor the hole and electron injection into OLEDs. With increasing the molecular conjugated length, the absorption and emission spectra exhibit red shifts to some extent and are in good agreement with the experimental ones. Also, the calculated emission spectra range from 330 to 440 nm. All the calculated show that the star‐shaped molecules are promising as blue light emitting materials     

Optical absorption and emission properties of fluoranthene, benzo[k]fluoranthene, and their derivatives. A DFT study

Fluoranthene and benzo[k]fluoranthene-based oligoarenes are good candidates for organic light-emitting diodes (OLEDs). In this work, the electronic structure and optical properties of fluoranthene, benzo[k]fluoranthene, and their derivatives have been studied using quantum chemical methods. The ground-state structures were optimized using the density functional theory (DFT) methods. The lowest singlet excited state was optimized using time-dependent density functional theory (TD-B3LYP) and configuration interaction singles (CIS) methods. On the basis of ground- and excited-state geometries, the absorption and emission spectra have been calculated using the TD-DFT method with a variety of exchange-correlation functionals. All the calculations were carried out in chloroform medium. The results show that the absorption and emission spectra calculated using the B3LYP functional is in good agreement with the available experimental results. Unlikely, the meta hybrid functionals such as M06HF and M062X underestimate the absorption and emission spectra of all the studied molecules. The calculated absorption and emission wavelength are more or less basis set independent. It has been observed that the substitution of an aromatic ring significantly alters the absorption and emission spectra.     

Electronic properties of anthracene derivatives for blue light emitting electroluminescent layers in organic light emitting diodes: a density functional theory study

Molecular level parameters are investigated computationally to understand the factors that are responsible for the higher efficiency in derivatives of 9,10-bis(1-naphthyl)anthracene (alpha-ADN), 9,10-bis(2-naphthyl)anthracene (beta-ADN), their tetramethyl derivatives (alpha,beta-TMADN) and the t-Bu derivative (beta-TBADN) as blue light emitting electroluminescent (EL) layers in organic light emitting diodes (OLEDs). DFT studies at the B3LYP/6-31G(d,p) level have been carried out on the substituted anthracenes. The absorption spectra are simulated using time dependent DFT methods (TD-DFT) whereas the emission spectra are approximated by optimizing the excited state by HF/CI-Singles and then carrying out the vertical CI calculations by the TD-DFT method. The reorganization energy for estimating the hole and electron transport is calculated. The transfer integrals between parallely stacked molecules in the bulk state are estimated by calculating the electronic splitting. The substituted anthracenes are compared with unsubstituted anthracene and yet untested 9,10-dianthrylanthracene (TANTH). A larger and slower buildup of the electrons and holes in the EL layer, due to the higher reorganization energy and smaller electronic coupling between the adjacent molecules could lead to an increase in hole-electron recombination in the layer and thus increase the efficiency.     

Theoretical study on dithieno[3,2-b:2′,3′-d]phosphole derivatives: high-efficiency blue-emitting materials with ambipolar semiconductor behavior

Phosphole-based systems due to the unique electronic and optical properties have recently been paid much attention as optoelectronic materials. In this work, the relationship among the electronic structure, charge injection, and transport was investigated for five derivatives of dithieno[3,2-b:2′,3′-d]phosphole (systems 1–5). The structures of systems 1–5 in the ground (S₀) and the lowest singlet excited (S₁) states were optimized at the HF/6-31G* and CIS/6-31G* levels of theory, respectively. Based on these structures, electronic spectra were calculated by time-dependent density functional theory. The simulated emission peaks of five phosphole derivatives locating at the blue–green region (448–516 nm), are in good agreement with the experimental data. Compared with tris-(8-quinolinolate) aluminum (III) (Alq₃), normally used as an excellent electron transporter, systems 1–5 show a significant improvement in electron affinity (EA) due to σ*–π* hyperconjugation, which can effectively promote ability of electron injection. The small differences between λ _h and λ _e for systems 1–5 (0.06–0.14 eV) facilitate charge transfer balance, which suggests systems 1–5 can act as potential ambipolar materials. Owing to good rigidity, low-lying LUMO levels, delocalized frontier molecular orbitals, and the small reorganization energies, the five derivatives of dithieno[3,2-b:2′,3′-d]phosphole are expected to be high-efficiency blue materials in single-layer OLEDs.     

Toward functional pi-conjugated organophosphorus materials: design of phosphole-based oligomers for electroluminescent devices

The photophysical, electrochemical, and optoelectronic properties of conjugated systems incorporating dibenzophosphole or phosphole moieties are described. Dibenzophosphole derivatives are not suitable materials for OLEDs due to their weak photoluminescence (PL) in the solid state and the instability of the devices. Variation of the substitution pattern of phospholes and chemical modification of their P atoms afford thermally stable derivatives, which are photo- and electroluminescent. Comparison of the optical properties of solution and thin film of thioxophospholes shows that these compounds do not form aggregates in the solid state. This property, which is also supported by an X-ray diffraction study of three novel derivatives, results in an enhancement of the fluorescence quantum yields in the solid state. In contrast, (phosphole)gold(I) complexes exhibit a broad emission in thin film, which is due to the formation of aggregates. Single- and multilayer OLEDs using these P derivatives as the emissive layer have been fabricated. The emission color of these devices and their performances vary with the nature of the P material. Interestingly, di(2-thienyl)thiooxophosphole is an efficient host for the red dopant DCJTB, and devices using the gold complexes have broad emission spectra.     

Thermische,nichtkatalysierte Cycloadditionen der Acrylverbindungen an Cycloheptatrien

The cycloaddition reactions of cycloheptatriene with acrylonitrile and methyl acrylate have been investigated in some detail. The exo ( 1 ) and endo ( 2 ) adducts resulting from the [2+2+2]-cycloaddition of acrylic components to the 2,5-positions of cycloheptatriene have been separated and the structures have been elucidated by NMR. The by-products are 7-endo-substitued derivatives of bicyclo[4,2,1]nona-2,4-diene ( 3 ), resulting from the formal [6+2]-cycloaddition to the 1,6-positions of cycloheptatriene. The mechanism of their formation is discussed. Irradiation (λ = 253,7 nm) of 3 in various solvents gave an almost quantitativ yield of [2+2]-cyclodimers of the 14 type. No intramolecular photocyclization of 3 to cyclobutenes 13a and/or 13b was observed.     

Deep Red to Near‐Infrared Emitting Rhenium(I) Complexes: Synthesis,Characterization, Electrochemistry,Photophysics, and Electroluminescence Studies

A series of triarylamine‐containing tricarbonyl rhenium(I) complexes, [BrRe(CO)₃(N^N)] (N^N=5,5′‐bis(N,N‐diaryl‐4‐[ethen‐1‐yl]‐aniline)‐2,2′‐bipyridine), has been designed and synthesized by introducing a rhenium(I) metal center into a donor‐π‐acceptor‐π‐donor structure. All of the complexes showed an intense broad structureless emission band in dichloromethane at around 680–708 nm, which originated from an excited state of intraligand charge transfer (³ILCT) character from the triarylamine to the bipyridine moiety. Upon introduction of the bulky and electron‐donating pentaphenylbenzene units attached to the aniline groups, the emission bands were found to be red shifted. The nanosecond transient absorption spectra of two selected complexes were studied, which were suggestive of the formation of an initial charge‐separated state. Computational studies have been performed to provide further insight into the origin of the absorption and emission. One of the rhenium(I) complexes has been utilized in the fabrication of organic light‐emitting diodes (OLEDs), representing the first example of the realization of deep red to near‐infrared rhenium(I)‐based OLEDs with an emission extending up to 800 nm.     

Theoretical design of blue emitting materials based on symmetric and asymmetric spirosilabifluorene derivatives

Equilibrium ground state geometry configurations and their relevant electronic properties of four experimentally reported asymmetric spirosilabifluorene derivatives are calculated by the HF(DFT)/6-31G(d) method. Their excited state geometries are investigated using the CIS/6-31G(d) method. The absorption and emission spectra are evaluated using the TD-B3LYP/6-31G(d) and TD-PBE0/6-31+G(d) levels both in gas phase and CHCl₃ solvent. Our results show an excellent agreement with the experimental data on their optical properties. To predict the substitution effect, the H/R (R = –NO₂, –CN, –NH₂ and –OCH₃) substituted symmetric and asymmetric spirosilabifluorene derivatives are also investigated, and the optical properties of H/R substituted derivatives are predicted in gas phase and CHCl₃ solvent. In comparison with the parent compound, significant red-shift is predicted for the emission spectra of the di-substituted symmetric derivatives with –NH₂ (96 nm), –OCH₃ (61 nm) and the push–pull (containing both –NH₂ and –NO₂) derivative (56 nm). It is found that the performance and the optical properties of these derivatives can be improved by adding push–pull substitutents. The largest change in the electronic and optical properties of this system can be obtained upon symmetric di-substitution among mono-, di-, tri- and tetra-substitutions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of substituents on synthetic analogs of chlorophylls. Part 3: The distinctive impact of auxochromes at the 7- versus 3-positions

Assessing the effects of substituents on the spectra of chlorophylls is essential for gaining a deep understanding of photosynthetic processes. Chlorophyll a and b differ solely in the nature of the 7-substituent (methyl versus formyl), whereas chlorophyll a and d differ solely in the 3-substituent (vinyl versus formyl), yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13(1)-oxophorbines that contain ethynyl, acetyl, formyl and other groups at the 3-, 7- and/or 13-positions. Substituent effects on the absorption spectra are well accounted for using Gouterman's four-orbital model. Key findings are that (1) the dramatic difference in auxochromic effects of a given substituent at the 7- versus 3- or 13-positions primarily derives from relative effects on the LUMO+1 and LUMO; (2) formyl at the 7- or 8-position effectively "porphyrinizes" the chlorin and (3) the substituent effect increases in the order of vinyl < ethynyl < acetyl < formyl. Thus, the spectral properties are governed by an intricate interplay of electronic effects of substituents at particular sites on the four frontier MOs of the chlorin macrocycle.     

DFT/TDDFT studies on the electronic structures and spectral properties of rhenium(I) pyridinybenzoimidazole complexes

The electronic structures and spectral properties of three Re(I) complexes [Re(CO)3XL] (X = Br, Cl; L = 1-(4-5'-phenyl-1,3,4-oxadiazolylbenzyl)-2-pyridinylbenzoimidazole (1), 1-(4-carbazolylbutyl)-2-pyridinylbenzoimidazole (2), and 2-(1-ethylbenzimidazol-2-yl)pyridine (3)) were investigated theoretically. The ground and the lowest lying triplet excited states were fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. TDDFT/PCM calculations have been employed to predict the absorption and emission spectra starting from the ground and excited state geometries, respectively. The lowest lying absorptions were calculated to be at 481, 493, and 486 nm for 1-3, respectively, and all have the transition configuration of HOMO-->LUMO. The lowest lying transitions can be assigned as metal/ligand-to-ligand charge transfer (MLCT/LLCT) character for 1, ligand-to-ligand charge transfer (LLCT) character for 2, and mixed MLCT/LLCT and intraligand pi-->pi* charge transfer (ILCT) character for 3. The emission of 1 at 551 nm has the MLCT/(3)LLCT character, 2 has the (3)MLCT/(3)LLCT character at 675 nm, and the 651 nm transition of 3 has the character of (3)MLCT/(3)LLCT/(3)ILCT. Ionization potentials (IP) and electron affinities (EA) calculations show that the comparable EA and smaller IP values and the relatively balanceable charges transfer ability of 2 with respect to 1 and 3 result in the higher efficiency of OLEDs. The calculated results show that the absorption and emission transition character and device's efficiency can be changed by altering the ancillary ligands.     

Synthesis,structures, optical and electrochemical properties,and complexation of 2,5-bis(pyrrol-2-yl)phospholes

2,5-Bis(pyrrol-2-yl)phosphole derivatives were prepared using the reaction of titanacycles, generated in situ from a Ti^II reagent and pyrrole-capped 1,6-heptadiynes, with dichloro(phenyl)phosphine. The 2,5-bis(pyrrol-2-yl)phosphole derivatives were found to possess narrower optical HOMO–LUMO gaps and less positive oxidation potentials than those of previously reported 2,5-diarylphosphole analogs. This demonstrates that the intrinsic nature of the electron excessive pyrrole subunits as well as the effective π-conjugation over the coplanar heterole rings. The σ³-P type 2,5-bis(5-phenylpyrrol-2-yl)phosphole underwent complexation with AuCl(SMe₂) and PtCl₂ to yield the respective AuCl–monophosphine and PtCl₂–bisphosphine complexes. In the square planar Pt^II complex, the pyrrolic NH protons were found to form intramolecular hydrogen bonds with the chlorine atoms that gave rise to symmetrically split, parallel π-chromophores linked by two Pt–P bonds. Density functional theory calculations on a Pt^II model complex suggested that this cooperative interaction induces a significant split of the original LUMOs of the symmetrical π-conjugated ligands.     

TDDFT Study of the Electronic Structure,Absorption and Emission Spectra of the Light Emitters of the Amazing Firefly Bioluminescence and Solvation Effects on the Spectra

The ground and excited state properties of luciferin (LH₂) and oxyluciferin (OxyLH₂), the bioluminescent chemicals in the firefly, have been characterized using density functional theory (DFT) and time dependent DFT (TDDFT) methods. The effects of solvation on the electronic absorption and emission spectra of luciferin and oxyluciferin were predicted with a self‐consistent isodensity polarized continuum model of the solvent using TDDFT. The S₀→S₁ vertical excitation energies in the gas phase and in water were obtained. Optimizations of the excited state geometries permitted the first predictions of the fluorescence spectra for these biologically important molecules. Shifts in both of the absorption and emission spectra on proceeding from the gas phase to aqueous solution were also predicted.     

Circularly Polarized Luminescence from Axially Chiral BODIPY DYEmers: An Experimental and Computational Study

With our new home‐built circularly polarized luminescence (CPL) instrument, we measured fluorescence and CPL spectra of the enantiomeric pairs of two quasi‐isomeric BODIPY DYEmers 1 and 2 , endowed with axial chirality. The electronic circular dichroism (ECD) and CPL spectra of these atropisomeric dimers are dominated by the exciton coupling between the main π–π* transitions (550–560 nm) of the two BODIPY rings. Compound 1 has strong ECD and CPL spectra (g_lum=4×10^?3) well reproduced by TD‐DFT and SCS‐CC2 (spin‐component scaled second‐order approximate coupled‐cluster) calculations using DFT‐optimized ground‐ and excited‐state structures. Compound 2 has weaker ECD and CPL spectra (g_lum=4×10^?4), partly due to the mutual cancellation of electric–electric and electric–magnetic exciton couplings, and partly to its conformational freedom. This compound is computationally very challenging. Starting from the optimized excited‐state geometries, we predicted the wrong sign for the CPL band of 2 using TD‐DFT with the most recommended hybrid and range‐separated functionals, whereas SCS‐CC2 or a DFT functional with full exact exchange provided the correct sign.     

用含时密度泛函方法研究和设计推拉结构的荧光分子

应用密度泛函理论(DFT)和含时密度泛函理论(TDDFT)方法及连续极化模型研究了六种荧光材料分子基态和第一激发态的电子结构性质.这六种分子是:3-(二氰亚甲基)-5,5-二甲基-1-(3-[9-(2-乙基-己基)-咔唑基]-乙烯基)环己烷(DCDHCC),DCDHCC2,3-(二氰亚甲基)-5,5-二甲基-1-(4-二苯基氨基-苯乙烯基)环己烷(DCDPC),DCDPC2,3-(二氰亚甲基)-5,5-二甲基-1-(4-[9-咔唑基]-乙烯基)环己烷(DCDCC)和3-(二氰亚甲基)-5,5-二甲基-1-(4-二甲基氨基-苯乙烯基)环己烷(DCDDC).它们可作为有机发光显示器件的发光材料.比较了PBE0、M06、BMK、M062X和CAM-B3LYP五种泛函,其中BMK方法很好地再现了各个分子在丙酮溶剂中的吸收和发射光谱.同时计算了分子的电子亲和能和电离势并用于评价分子的电荷注入性质.研究表明,当使用双π桥和双受体时,分子的发射光谱会红移到理想的发光区域.据此设计了两个新的分子DCDCC2和DCDDC2,它们分别是DCDCC和DCDDC的双支对应分子.计算结果表明这两个分子也具有作为荧光发射体的良好性质.     

Cyclophanes of perylene tetracarboxylic diimide with different substituents at bay positions

Cyclophanes of perylene tetracarboxylic diimides (PDIs) with different substituents at the bay positions, namely four phenoxy groups at the 1,7-positions (1), four piperidinyl groups at the 1,7-positions (2), and eight phenoxy groups at the 1,6,7,12-positions (3) of the two PDI rings, have been synthesized by the condensation of perylene dianhydride with amine in a dilute solution. These novel cyclophanes were characterized by (1)H NMR spectroscopy, MALDI-TOF mass spectrometry, electronic absorption spectroscopy, and elemental analysis. The conformational isomers of cyclophanes substituted with four piperidinyl groups at the 1,7-positions (2 a and 2 b) were successfully separated by preparative TLC. The main absorption band of the cyclophanes shifts significantly to the higher energy side in comparison with their monomeric counterparts, which indicates significant pi-pi interaction between the PDI units in the cyclophanes. Nevertheless, both the electronic absorption and fluorescence spectra of the cyclophanes were found to change along with the number and nature of the side groups at the bay positions of the PDI ring. Time-dependent DFT calculations on the conformational isomers 2 a and 2 b reproduce well their experimental electronic absorption spectra. Electrochemical studies reveal that the first oxidation and reduction potentials of the PDI ring in the cyclophanes increase significantly compared with those of the corresponding monomeric counterparts, in line with the change in the energy of the HOMO and LUMO according to the theoretical calculations.     

Theoretical investigations on electronic structures and photophysical properties of novel bridged triphenylamine derivatives

It has been proved that triphenylamine (TPA) derivatives can be excellent candidates for hole‐transporting materials in organic light‐emitting diodes (OLEDs). To improve on the thermal and morphological stability, a fully diarymethylene‐bridged TPA derivative (FATPA) which has been proven to enhance electroluminescent (EL) efficiency was synthesized. On the basis of FATPA, two series of novel bridged TPA derivatives have been designed by using diarylmethylene (Series A) or dimethyfluorene (Series B) as the linkage between the ortho‐positions of the phenyl rings in this work (see Fig. 1 ). To reveal the relationships between electronic structures and photophysical properties of these novel functional materials, an in‐depth theoretical investigation was elaborated via quantum chemical calculations using the density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods. In addition, the feasibility of using these bridged TPA derivatives as host in the device of ITO/MoO₃/NPB/mCP/host:Ir(ppy)₃/TAZ/LiF/Al was also evaluated, which including the discussion to their energy levels match with adjacent layers and energy transfer from host to guest. These calculated results show that photophysical properties can be easily tuned by the introduction of various substituent groups into the bridged TPA derivatives, such as the highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), the energies difference between the HOMOs and LUMOs (Δ_H‐L), the lowest singlet (E_S) and triplet (E_T) excitation energies, ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ) and the absorption and emission spectra, indicating that these bridged TPA derivatives have great potential applications for OLEDs. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

3,4,9,10-Perylenetetracarboxylic Acid Derivatives, Their Spectral Behavior and Their Chemical Interaction with Hydrated Iron Oxide Nanopar

The photophysical properties such as electronic absorption, excitation and emission spectra as well as molar absorptivity and fluorescence quantum yield of N,N‐bis(pyrimidenyl)‐3,4,9,10‐perylenetetracarboxylic diimide (PmPBD), N,N‐bis(pyridenyl)‐3,4,9,10‐perylenetetracarboxylic diimide (PyPBD) and N,N‐bis(4‐methylpyridenyl)‐3,4,9,10‐perylenetetracarboxylic diimide (MPyPBD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield ((_f) is solvent dependent. Perylene derivatives under investigation undergo molecular aggregation to dimmer or larger aggregates in water. Dye solution in dimethylformmaide (DMF) gives laser emission at 565 nm upon pumping with 337.1 nm nitrogen laser pulse. The excitation energy transfer from 7‐dimethylamino‐4‐methylcoumarine (DMC) to PmPBD has been studied to improve the laser emission of PmPBD. The value of energy transfer rate constant (k_ET) and critical transfer distance (R₀) indicate a F?rster type energy transfer mechanism. There is a large interaction between the perylene compounds under investigation and the hydrated nanoparticles in the excited state therefore the fluorescence quenching rate constant of these derivatives by hydrated iron oxide nanoparticles has a large value.     

A C4N4 Diaminopyrimidine Fluorophore

A new scaffold for producing efficient organic fluorescent materials was identified: 2,5-diamino-4,6-diarylpyrimidine featuring a C4N4 elemental composition. Single-step installation of two aryl groups at the 4,6-positions of the pyrimidine core delivered fluorescent organic materials in a modular fashion. A range of fluorescent compounds with distinct absorption/emission properties was readily accessed by changing the aromatic attachments. A generally high absorption coefficient and quantum yield were observed, including C4N4 derivatives that could fluoresce even in the solid state. The two amino groups at the 2,5-positions of the pyrimidine were essential for intense fluorescence with a large Stokes shift, which was corroborated by structural relaxation to a p-iminoquinone-like structure in the excited state. Besides live-cell imaging capabilities, fluorescent labeling of a protein involved in autophagy elucidated a new protein–protein interaction, supporting potential utility in bioimaging applications.