Synthesis, characterization and photophysical processes of fluorene derivative containing naphthalene nucleus

A novel luminescent compound, 9,9-bis[4'-(beta-naphthyl-methacrylate)phenyl]fluorene (F-NMAP) is synthesized by Heck reaction of beta-naphthyl methacrylic ester (NMAE) and 9,9-bis(4'-iodophenyl)-fluorene (BIPF). The structure is characterized by MS, 1H NMR, IR, and UV-vis spectroscopy. The photophysical processes of F-NMAP have been carefully investigated by UV-vis absorption and fluorescence spectra. The results show that the compound emits blue and blue-violet light. The luminescence quantum yield is 0.652 in ethanol and the emission spectra exhibit obvious solvent effect. With the increase in polarity of solvents, the fluorescence spectra change obviously and appear blue shift at room temperature. The light emitting can be quenched by both electron donor, N,N-dimethylaniline (DMA), and electron acceptor, dimethylterephthalate (DMTP). On adding gradually, DMA or DMTP into the solution of F-NMAP, the emission intensities of fluorescence are unusually increased. But when the concentration of DMA or DMTP goes beyond a certain scope, the emission intensities of fluorescence are gradually decreased. Simultaneously, the maximum emission peaks of F-NMAP-added DMA are blue-shifted and the maximum emission peaks of F-NMAP-added DMTP are red-shifted, respectively. Moreover, interactions between F-NMAP and fullerene (C60), or carbon nanotubes (CNTs) are also studied by fluorescent quenching where the processes follow the Stern-Volmer equation.     

Photophysical processes of a fluorene derivative containing 1,3,4-oxadiazole

The photophysical processes of 9,9-bis[4'-[2'-phenyl-5'-(3'-(methacryl-amido)phenyl)]-1',3',4'-oxadiazolylphenyl]fluorene (F-MAOP) formed by Heck reaction of 9,9-bis(4'-iodophenyl)fluorene (F-IP) and 2-phenyl-5-[3'-(methacrylamido)phenyl]-1,3,4-oxadiazole (OXD) have been carefully studied. The results show that the compound emits blue and blue-violet light and the emission spectra exhibit obvious solvent effect. With the increase of polarity of solvents, the fluorescence spectra change obviously and appear blue shift at room temperature. In addition, the light-emitting can be quenched by both electron donor (N,N-dimethylaniline, DMA) and electron acceptor (C60). When N,N-dimethylaniline is gradually added into the solution of F-MAOP, the emission intensities of fluorescence are unusually increased. But when the concentration of DMA beyond a certain scope, the emission intensities of fluorescence are gradually decreased. The dimolecular exciplex between F-MAOP and C60 are formed and the quenching effect follows the Stern-Volmer equation. Moreover, interaction between F-MAOP and carbon nanotubes (CNTs) is also studied by fluorescent quenching.     

Synthesis and photophysics of novel 8-hydroxyquinoline aluminum metal complex with fluorene units

A novel luminescent metal complex, (MQPF)3Al2, with 8-hydroxyquinoline aluminum and 9,9-diphenylfluorene was synthesized. The optical properties were investigated by UV-vis absorption and fluorescence emission spectra. The results showed that the luminescence quantum yield of (MQPF)3Al2 was 0.612 in THF and it emitted red light with the band gap of 3.18 eV estimated from the onset absorption. The emission spectra exhibited obvious solvent effect. With the increase of polarity of solvents the fluorescence spectra changed obviously and appeared blue shift about 60 nm at room temperature. In addition, the light-emitting can be quenched by both electron donor (N,N-dimethylaniline) and electron acceptor (Fullerene), where the processes followed the Stern-Volmer equation. However, when adding 1,4-dicyanobenzene (DCB) which was a stronger electron acceptor to the solution of (MQPF)3Al2, the fluorescent intensity was increased.     

4-[2-(二甲氨基)乙氧基]-N-十八烷基-1,8-萘酰亚胺荧光染料的合成及其性能研究

以4-溴-1,8-萘酐为原料,合成脂溶性4-[2-(二甲氨基)乙氧基]-N-十八烷基-1,8-萘酰亚胺。对其进行了1H NMR和IR表征。考察了荧光染料在DMF、乙腈、丙酮、乙酸乙酯和乙醚5种溶剂中的荧光光谱和吸收光谱,发现由于溶剂效应,随溶剂极性由小到大,荧光光谱和吸收光谱的最大峰值波长逐渐红移。考察了不同金属离子和pH对荧光染料荧光光谱的影响,结果表明荧光强度随Fe3+、Zn2+、Co2+浓度增大而逐渐增强,Fe3+的影响最为显著;当pH<7时,荧光强度随着pH的降低逐渐增强;进一步考察了Fe3+、Zn2+、Co2+对吸收光谱的影响,结果发现吸收光谱均蓝移。分析认为荧光染料的光致电子转移被阻碍,实验结果表明,合成的新型荧光染料可用于溶液中金属离子和pH的检测。     

Ratiometric, fluorescent BODIPY dye with aza crown ether functionality: synthesis, solvatochromism, and metal ion complex formation

A new pH and metal ion-responsive BODIPY-based fluorescent probe with an aza crown ether subunit has been synthesized via condensation of 4-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-yl)-benzaldehyde with the appropriate 1,3,5,7-tetramethyl substituted boron dipyrromethene moiety. Steady-state and time-resolved fluorometries have been used to study the spectroscopic and photophysical characteristics of this probe in various solvents. The fluorescence properties of the dye are strongly solvent dependent: increasing the solvent polarity leads to lower fluorescence quantum yields and lifetimes, and the wavelength of maximum fluorescence emission shifts to the red. The Catalan solvent scales are found to be the most suitable for describing the solvatochromic shifts of the fluorescence emission. Fluorescence decay profiles of the dye can be described by a single-exponential fit in nonprotic solvents, whereas two decay times are found in alcohols. Protonation as well as complex formation with several metal ions are investigated in acetonitrile as solvent via fluorometric titrations. The aza crown ether dye undergoes a reversible (de)protonation reaction (pKa = 0.09) and shows a approximately 50 nm blue shift in the excitation spectra and a 10-fold fluorescence increase upon protonation. The compound also forms 1:1 complexes with several metal ions (Li(+), Na(+), Mg(2+), Ca(2+), Ba(2+), Zn(2+)), producing large blue shifts in the excitation spectra and significant cation-induced fluorescence amplifications.     

An exceptional red shift of emission maxima upon fluorine substitution

The effect of perfluorination on photophysical properties was investigated through synthesis and photophysical characterization of two isostructural donor-acceptor-donor dye molecules. The synthesis of two versatile fluorinated benzene compounds, 1,4-difluoro-2,5-diperfluorooctylbenzene (1) and 1,4-dibromo-2,5-difluoro-3,6-diperfluorooctylbenzene (2), is presented. The X-ray structure of 2 has been determined and shows that the perfluorinated octyl chains segregate from the benzene rings in the solid state, giving rise to a layered structure. The further synthesis through Suzuki coupling reactions using 4-formylbenzeneboronic acid with (2) and 1,4-dibromo-2,5-dioctylbenzene (3) gave, respectively, 1,4' '-diformyl-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (4) and 1,4' '-diformyl-2',5'-dioctyl-p-terphenylene (5). The condensation of the dialdehydes 4 and 5 with 9,10-phenanthrenequinone and ammoniumbicarbonate in glacial acetic acid gave the dye molecules 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (6) and 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-dioctyl-p-terphenylene (7), respectively. The UV-vis spectra of the two molecules are nearly identical, whereas the fluorescence spectra are very different. Compound 7 shows blue fluorescence with little solvent dependence (lambda(emission) = 410 nm in THF, CH2Cl2, and hexane), whereas compound 6 shows a highly solvent-dependent emission wavelength (lambda(emission) = 583 nm in THF, lambda(emission) = 560 nm in CH2Cl2, and lambda(emission) = 450 nm in hexane). The fluorescence red shift of compound 6 in a series of solvents with different polarity is discussed using the Lippert-Mataga equation. Fluorescence lifetime and quantum yields were also determined. Ultraviolet photoelectron spectroscopy (UPS) was performed on thin films of compound 6 and 7 on a gold substrate. The observed ionization potential was 6.15 eV for 6 and 5.85 eV for 7" [correction].     

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.     

Synthesis and solvent-dependent photophysics of a novel fluorescent triazole-coumarin-based dye

Synthesis of a new coumarin-triazole-based dye and its photophysical parameters such as absorption, fluorescence emission, and fluorescence quantum yield were investigated. Studies have shown that the present dye has symmetry with a mirror image, especially in the ethanol solvent, with respect to the absorption and fluorescence spectra. As a result of the UV-vis and fluorescence spectroscopy techniques used, it was determined that absorption and emission spectra were shifted to the red with increasing solvent polarity. In addition, the spectral data of the synthesized compound exhibited that the stokes shifts are small, usually less than 50 nm, and the quantum yields are significantly high. In accordance with the results obtained, it can be stated that this novel dye synthesized here can offer an insight into application in sensor applications as analytical or biosensors, optoelectronic devices, and medicine industry.     

A KIND OF FLUORESCENCE PROBE TO STUDY THE KINETICS OF POLYMERIZATION PROCESS

Fluorescence properties of 1-pheny1-3-(4'-nitrophenyl) pyrazoline (PNP) were studied inbulk polymerization process of methylmethacrylate (MMA). The fluorescence intensity of PNPwas enhanced and the emission maximum was blue shifted with the polymerization progress. Inthe period of auto-acceleration of the polymerization the enhancement of fluorescence intensityand blue shift of peak wavelength in spectra could be observed evidently. This means that thesolvatochromic properties of PNP are influenced not only by the solvent polarity but also by theviscosity of the medium (especially by the phase transitiott). In solid state PNP emits from thecharge transfer excited state without solvent relaxation. The transient emission spectra and theresults from Bakhshiev model of solvent relaxation coincide with that from the polymerizationexperiment.     

Sensitized emission of luminescent lanthanide complexes based on 4-naphthalen-1-yl-benzoic acid derivatives by a charge-transfer process.

The photophysical properties of 4-naphthalen-1-yl-benzoic acid ligands and their Eu(III)-cored complexes were systematically investigated to elucidate the effective energy-transfer pathway in luminescent lanthanide complexes. A series of 4-naphthalen-1-yl-benzoic acid ligands, such as 4-naphthalen-1-yl-benzoic acid (NA-1), 4-[4-(4-methoxyphenyl)-naphthalen-1-yl]-benzoic acid (NA-2), and 4-{4-[4-(4-methoxyphenyl)-naphthalen-1-yl]-benzyloxy}-benzoic acid (NA-3), were synthesized and utilized for the synthesis of their Eu(III)-cored complexes, corresponding to NAC-1, NAC-2, and NAC-3. The fluorescence spectra of NA-1 and NA-2 show large Stokes shifts with increasing solvent polarity. These large Stokes shifts might be dominantly due to the formation of an intramolecular charge transfer (ICT) complex in the excited state. Also, the intensive luminescence of the Eu(III) ions by the photoexcitation of the ligand in NAC-1 and NAC-2 in polar solvents supports that the energy transfer from the ligand to the Eu(III) ion takes place efficiently. In the case of NA-3, which has a -CH2OPh- group that acts as a blocking group, there is no dependence of the fluorescence spectrum on the solvent nature and no luminescence of the Eu(III) ions by the photoexcitation of the ligand, indicating no formation of the ICT state. This can be due to the fact that the formation of the ICT state in NA-3 was prevented because the -OCH2- group acts as a blocking group by interrupting the pi-conjugation between the benzoic acid and the naphthalene unit. From these photophysical studies, we suggest that the ICT state plays a very important role in the energy-transfer pathway from the ligand to the Eu(III) ion. To our best knowledge, this is the first demonstration of sensitized emission of luminescent lanthanide complexes based on 4-naphthalen-1-yl-benzoic acid derivatives by the charge-transfer process.     

Effet de la polarité du solvant sur les propriétés des états électroniques excités du 1,1′-binaphtyle: étude par spectroscopie UV-visible

A UV-vis emission spectroscopy study of the flexible molecule, 1,1′-binaphtyl as a function of solvent polarity allows one to obtain information on the excited singlet states. We show the existence of a charge transfer (CT) character state. This CT is evidenced by the solvent polarity effect, the measurement of polarization ratio and finally by comparison of the ratio intensities of phosphorescence and fluorescence.     

3,14‐Bis(p‐nitrophenyl)‐17,17‐dipentyltetrabenzo[a,c,g,i]‐fluorene: A New Fluorophore Displaying Both Remarkable Solvatochromism and Crystalline‐Induced Emission

A series of 17,17‐dialkyl‐3,14‐diaryltetrabenzofluorenes were efficiently prepared by using Suzuki–Miyaura cross‐coupling reactions of the corresponding 3,14‐dibromo derivatives. Studies of the unique fluorescence properties of these compounds showed that they display intense blue to yellow fluorescence with high quantum yields in the solution state and blue to orange fluorescence with moderate quantum yields in the solid state. In addition, the fluorescence wavelength of the bis(p‐nitrophenyl) derivative is remarkably solvent‐dependent in a manner that correlates with the solvent polarity parameter E_T(30). The results of density function theory calculations suggest that the intramolecular charge‐transfer character of the HOMO–LUMO transition is responsible for the large solvent effect. Moreover, addition of water to a tetrahydrofuran (THF) solution of this compound leads to quenching of the yellow fluorescence owing to an increase in the solvent polarity. However, when the amount of water fraction exceeds 70 %, a new fluorescence band appears at the same orange‐red emission wavelength as that of the solid‐state fluorescence. This observation suggests the occurrence of a crystallization‐induced emission (CIE) phenomenon in highly aqueous THF.     

Effect of Solvent Polarity on Excited-State Double Proton Transfer Process of 1, 5-Dihydroxyanthraquinone

The excited-state double proton transfer (ESDPT) properties of 1, 5-dihydroxyanthraquinone (1, 5-DHAQ) in various solvents were investigated using femtosecond transient absorption spectroscopy and the DFT/TDDFT method. The steady-state fluorescence spectra in toluene, tetrahydrofuran (THF) and acetonitrile (ACN) solvents presented that the solvent polarity has an effect on the position of the ESDPT fluorescence emission peak for the 1, 5-DHAQ system. Transient absorption spectra show that the increasing polarity of the solvent accelerates the rate of excited state dynamics. Calculated potential energy curves analysis further verified the experimental results. The ESDPT barrier decreases gradually with the increase of solvent polarity from toluene, THF to ACN solvent. It is convinced that the increase of solvent polarity can promote the occurrence of the ESDPT dynamic processes for the 1, 5-DHAQ system. This work clarifies the mechanism of the influence of solvent polarity on the ESDPT process of 1, 5-DHAQ, which provides novel ideas for design and synthesis of new hydroxyanthraquinone derivatives.     

Comparison of the absorption, emission, and resonance Raman spectra of 7-hydroxyquinoline and 8-bromo-7-hydroxyquinoline caged acetate

To better understand the deprotection reaction of the new promising phototrigger compound BHQ-OAc (8-bromo-7-hydroxyquinoline acetate), we present a detailed comparison of the UV-vis absorption, resonance Raman, and fluorescence spectra of BHQ-OAc with its parent compound 7-hydroxyquinoline in different solvents. The steady-state absorption and resonance Raman spectra provide fundamental information about the structure, properties, and population distribution of the different prototropic forms present under the different solvent conditions examined. The species present in the excited states that emit strongly were detected by fluorescence spectra. It is shown that the ground-state tautomerization process of BHQ-OAc is disfavored compared with that of 7-HQ in aqueous solutions. The observation of the tautomeric form of BHQ-OAc in neutral aqueous solutions demonstrates the occurrence of the excited-state proton-transfer process, which would be a competing process for the deprotection reaction of BHQ-OAc in aqueous solutions.     

High boron content carboranyl-functionalized aryl ether derivatives displaying photoluminescent properties

The reaction of alpha,alpha'-bis(3,5-bis(bromomethyl)phenoxy-p-xylene (3) with 4 equiv of the monolithium salt of 1-Ph-1,2-C2B10H11 or 1-Me-1,2-C2B10H11 gave the corresponding neutral carboranyl-functionalized aryl ether derivatives closo-4 and closo-5, respectively. These compounds contain four closo clusters that were degraded using basic conditions with KOH in EtOH, affording the corresponding nido-6 and nido-7 as potassium salts. Nido species were also isolated with tetramethylammonium as cation giving compounds nido-8 and nido-9 in good yield. The potassium salts showed good solubility in water and polar solvents. All these compounds were characterized by 1H, 11B and 13C NMR spectroscopy and UV-vis. The electronic data in different solvents indicated a solvatochromic shift for all compounds and a red shift of the absorption maxima for the nido species with respect to the closo derivatives. These neutral and anionic carboranyl-functionalized aryl ether derivatives represent a new family of high boron content luminescent compounds that show strong fluorescence emission in different solvents at room temperature. This phenomenon is very interesting considering the fact that none of the precursors have such a property. The fluorescence emission depends on the cluster substituent (Ph or Me) and the solvent polarity. Additionally, the fluorescence emission intensity was clearly dependent on the solvent polarity; the closo species showed strongest fluorescence intensities in the non-polar solvents, while anionic species were highly emissive in polar solvents.     

MULTIFREQUENCY CROSS-CORRELATION PHASE FLUOROMETRY OF CHLOROPHYLL a FLUORESCENCE IN THYLAKOID AND PSII-ENRICHED MEMBRANES

The changes in plasma membrane polarity of polymorphonuclear leukocytes (PMN) during the activation of the respiratory burst were investigated by measuring the steady-state fluorescence emission spectra of 2-dimethylamino(6-lauroyl) naphthalene (Laurdan), which is known to be incorporated at the hydrophobic-hydro-philic interface of the bilayer, displaying spectral sensitivity to the polarity of its surroundings. Laurdan shows a marked steady-state emission blue shift in nonpolar solvents, with respect to polar solvents. Our results show a blue shift of the fluorescence emission spectra of Laurdan during activation of PMN with phorbol myristate acetate or AT-formyl-methionyl-leucyl-phenylalanine. These results suggest that the activation of the respiratory burst of PMN is accompanied by a decrease in polarity in the hydrophobic-hydrophilic interface of the plasma membrane.     

2-Amino-7-nitro-fluorenes in neat and mixed solvents-optical band shapes and solvatochromism

Femtosecond transient absorption spectroscopy of amino-nitro-fluorenes in the UV-visible range shows that the dynamic Stokes shift of the emission band is sensitive to infrared-active modes of the solvent. Bandshapes for stationary absorption and emission are needed to quantify the observed spectral evolution. They are reported for 2-amino-7-nitro-fluorene (ANF), 2-dimethylamino-7-nitro-fluorene (dM-ANF), and 2-di(n-butyl)amino-7-nitro-9-di(n-propyl)-fluorene (dBdP-ANF) in a variety of solvents. Bands broaden systematically with increasing solvent polarity. This effect is taken into account in an improved location of band positions. The resulting solvatochromic plots differ significantly from those that use peak positions of absorption spectra and fluorescence quantum distributions. Absorption spectra were also measured in aqueous solvent mixtures, and shifts are described by binding curves for hydrogen bonding and stepwise solvent exchange.     

Environment‐Sensitive Fluorescent Probe: A Benzophosphole Oxide with an Electron‐Donating Substituent

Electron‐donating aryl groups were attached to electron‐accepting benzophosphole skeletons. Among several derivatives thus prepared, one benzophosphole oxide was particularly interesting, as it retained high fluorescence quantum yields even in polar and protic solvents. This phosphole‐based compound exhibited a drastic color change of its fluorescence spectrum as a function of the solvent polarity, while the absorption spectra remained virtually unchanged. Capitalizing on these features, this phosphole‐based compound was used to stain adipocytes, in which the polarity of subcellular compartments could then be discriminated on the basis of the color change of the fluorescence emission.     

由蚕砂制备的碳量子点在不同激发、pH、金属离子、温度及极性环境下的荧光性质研究

碳量子点作为一种新兴的荧光纳米材料,具有粒径分布均匀、光稳定性好、激发-发射波长可调控、表面可修饰等优良的性质,兼具低毒性、生物相容性好等优点,在分析检测和生物成像等领域展现出广阔的应用前景。而蚕砂是家蚕的干燥粪便,简单易得。利用蚕砂作为碳量子点制备原料,采用微波合成的方法制备得到了一种平均水合粒径为4.86 nm,含氮、硫修饰的碳量子点材料,可作为针对激发波长、pH、金属离子浓度、温度及溶剂极性的变化有着显著响应特性的碳量子点型荧光探针。该探针的荧光最大发射波长随激发波长或pH的增加而红移;荧光强度随温度或pH的降低而增加;随着金属离子,特别是铜离子的加入而逐渐降低,并随着EDTA络离子的加入而逐渐回复。在多种溶剂中该探针均具有较好的溶解度,当换用不同极性的溶剂时,随着溶剂极性的增加荧光发射波长逐渐红移。荧光性质随多重环境参数变化为该碳量子点在未来的生物检测和成像领域提供了广阔的应用前景。     

Mesitylboron-substituted ladder-type pentaphenylenes: charge-transfer, electronic communication, and sensing properties

A series of dimesitylboron (B)- or ditolylamino (N)-substituted ladder-type pentaphenylenes (PP) has been designed and synthesized. The UV-vis absorption spectra of compounds BPPN, BPPB, and NPPN reveal an identical maximum wavelength at 432 nm, which indicates that the B and N centers have very similar contributions to the extended conjugation. A rather weak solvatochromism in the UV-vis absorption spectra is observed for compound BPPN, while a remarkable solvatochromic emission is achieved even though the distance between the B and the N centers is as huge as 22 A. The photoluminescence of BPPN shows a bathochromic shift of 108 nm when the solvent polarity is increased from cyclohexane (453 nm) to acetone (561 nm). Compound BPPN acts as a colorimetric and fluorescent chemosensor with high sensitivity (10(-5) M) and selectivity for F(-) over other halogen ions. By inhibiting the charge transfer (CT) from the N center to the B center, the intense green CT emission of compound BPPN rapidly switches into the sky-blue emission of PP when F(-) is bound to the B center. Furthermore, a CT emission can be switched "on" and "off" when compound BPPB is used as F(-) sensory material. Such an intramolecular CT emission between the two B centers has so far never been reported. Corresponding studies by cyclic voltammetry and differential pulse voltammetry reveal a two-step reduction of the two bridged B centers in compound BPPB, which might suggest that the charge delocalizes through the whole molecule and that the terminal redox centers communicate through the pentaphenylene bridge.