Solvatochromic Fluorescence Research Articles

Synthesis and Solvatochromic Fluorescence of Biaryl Pyrimidine Nucleosides

Fluorescent pyrimidine analogs containing a fused biphenyl unit were prepared in high yields using stereoselective N-glycosylation and Suzuki-Miyaura cross-coupling reactions. The resulting "push-pull" fluorophores exhibit highly solvatochromic emissions from twisted intramolecular charge-transfer (TICT) states.

Structure of donor–acceptor biphenyl derivatives in the excited state

This paper presents a study on structural changes of donor–acceptor derivatives of biphenyl: 4-hydroxy-4′-cyanobiphenyl, 4-hydroxy-2,6-dimethyl-4′-cyanobiphenyl and 4-methoxy-2,6-dimethyl-4′-cyanobiphenyl in the excited state. An analysis of spectral and photophysical parameters of those compounds was completed and quantum-chemical calculations were conducted in order to explain if the excited state of these molecules is a mesomerically stabilized less polar intramolecular charge transfer (MICT) state of near planar geometry, or a more polar one, with strongly decoupled intramolecular CT resembling a TICT state. A strong solvatochromism of fluorescence and values of dipole moment in the excited state suggest the TICT character of the emitting state, especially in compounds with a sterical hindrance. It was demonstrated that structural changes of excited derivatives containing an OH group, resulting from strong charge transfer from the donor subunit onto acceptor part of those molecules, are associated with so strong increase of acidity of studied compounds, that they can be included in the group of, so-called, “super” photoacids.

Solvatochromic fluorescence behavior of 2-amino-6-hydroxy-4-(3,4-dimethoxyphenyl)-pyrimidine-5-carbonitrile: A sensitive fluorescent probe for detection of pH and water composition in binary aqueous solutions

A new class of fluorescence sensor for detection of water in organic solvents based on photo-induced electron transfer (PET) of substituted pyrimidine appended with dimethoxyphenyl system has been designed and characterized. The probe 2-amino-6-hydroxy-4-(3,4-dimethoxyphenyl)-pyrimidine-5-carbonitrile AHDPC (I) was synthesized by one step three-component condensation reaction. The solvatochromic fluorescence behavior of AHDPC featuring electron withdrawing CN group, electron donating ―OCH3, NH2, OH groups and various π-conjugated backbones in varying polar and non-polar solvents has been investigated. The fluorescence of the compound exhibits red shift from its absorption spectra and correlated with solvent polarity. AHDPC exhibited significant spectral shifts in λem as a function of water composition in binary aqueous solvent systems. The changes are due to the specific interactions of AHDPC by intramolecular hydrogen bonding with water, photoinduced electron transfer as well as general solvent effect. The observed solvatochromic fluorescence characteristic of AHDPC could used as a new probe for micro-environmental polarity changes as well as a sensitive sensor for the determination of water composition in binary aqueous solutions. This study shows that due to the solvent sensitive emission, pyrimidine derivatives are good candidates to be used as fluorescent probes.

Synthesis and evaluation of photophysical properties of Series of π-conjugated oxazole dyes

Incorporation of π-conjugated spacers at the 2 or 5 position of a 2,5-disubstitutedaryloxazole led to new series of fluorescent dyes. They show emissions from visible to 700nm along with significant Stokes shift up to 208nm and a strong solvatochromic fluorescence. These compounds are easily accessible in one step through direct C–H bond functionalization.

Synthesis and Solvatofluorochromism Behaviors on Intramolecular Charge Transfer System of Novel D-π-A Dyes

Solvatochromic donor-π-acceptor (D-π-A) charge transfer dyes have been great attention from the viewpoint of their applicability as probes for the determination of solvent polarity and colorimetric chemosensors. In this work, novel solvatochromic fluorophore dyes based on D-π-A charge transfer system were designed and synthesized containing a strong electron-donating unit as a carbazole moiety and three different strong electron-withdrawing units. The corresponding molecular design and the optical properties of the D-π-A dyes were examined in various solutions with widely different polarity. The prepared dyes were found to exhibit a positive fluorescence solvatochromism. Furthermore, the energy properties of these dyes were also computationally optimized and calculated by computational simulation approaches using Material Studio 4.3 and electrochemical measurement.

Solvatofluorochromism and twisted intramolecular charge‐transfer state of the nile red dye

AbstractProfiles of the S1 potential energy surface of the Nile Red dye along the rotational coordinate of the amino group are computed using time‐dependent density functional theory (TDDFT) and XMCQDPT2/CASSCF. The calculated profiles exhibit two minima corresponding to a planar locally excited (LE) state and a twisted intramolecular charge transfer (TICT) state. The profiles calculated by time‐dependent density functional theory (TDDFT) depend on the weight of the hartree‐fock (HF) exchange in the functional: at 0% exchange, only the TICT minimum exists, whereas at 50% exchange and more there is only the LE minimum. The profiles obtained by TDDFT at 20–25% HF exchange are in qualitative agreement with that obtained by XMCQDPT2/CASSCF calculations. The energy of the charge transfer state is lowered due to the participation of doubly excited configurations and dynamic correlations, which is implicitly included in the density functionals. The solvent effects on the relative energies of the LE and TICT states and on the barrier height are studied using the polarizable continuum model. The effect of hydrogen bonds is studied for a complex of Nile Red with two water molecules. The solvatochromism of Nile Red fluorescence in aprotic polar solvents is explained by nonspecific solvation, which stabilizes the LE state and causes Nile Red fluorescence solvatochromism; in water and alcohols, it is explained by the formation of hydrogen bonds, which stabilize the TICT state and facilitate the LE‐to‐TICT transition. © 2012 Wiley Periodicals, Inc.

5-[4-(Dimethylamino)phenyl]-2-benzamidopyrazines: fluorescent dyes based on Cypridina oxyluciferin

To clarify the acyl substitution effect on the fluorescent property of Cypridina oxyluciferin analogs, which have the 4-(dimethylamino)phenyl group at C5, we compared the spectroscopic properties of benzamide 1b and its 2,6-dimethylphenyl derivative 1c in various solvents with those of acetamide 1a. Similarity of the fluorescence wavelengths of 1a–c indicates that the π-electronic conjugation in the excited singlet (S1) state is terminated at the acyl group and that the benzamide moiety in 1b has little effect on modulating the florescence color. The similar fluorescence solvatochromism of 1a–c reveals that their S1 states have a similar intramolecular charge transfer character. The fact that 1a–c have various fluorescence quantum yields and lifetimes depending on solvent polarity and hydrogen bonding interactions in solutions provides information about the decay processes competing with the fluorescence process in the S1 states. Among 1a–c, benzamide 1b exhibits the most sensitive variation of the fluorescence intensity depending on the solvent used. Similarity of the fluorescence spectra of 1a–c adsorbed in NaY zeolites was also observed, which indicates that the S1 states of 1a–c give mobile conformers in the NaY supercages. The relationship between the molecular structures of 1a–c and their spectroscopic properties will provide a guide for designing a new fluorophore based on Cypridina oxyluciferin.

Synthesis, solvatochromism, aggregation-induced emission and cell imaging of tetraphenylethene-containing BODIPY derivatives with large Stokes shifts

A series of tetraphenylethene-containing BODIPYs with emissions from visible to near-IR and large Stokes shifts up to 142 nm have been designed and synthesized. They show solvatochromic fluorescence and can be utilized as fluorescent visualizers for intracellular imaging.

Synthesis and Photophysical Properties of Biaryl-Substituted Nucleos(t)ides. Polymerase Synthesis of DNA Probes Bearing Solvatochromic and pH-Sensitive Dual Fluorescent and 19F NMR Labels

The design of four new fluorinated biaryl fluorescent labels and their attachment to nucleosides and nucleoside triphosphates (dNTPs) by the aqueous cross-coupling reactions of biarylboronates is reported. The modified dNTPs were good substrates for KOD XL polymerase and were enzymatically incorporated into DNA probes. The photophysical properties of the biaryl-modified nucleosides, dNTPs, and DNA were studied systematically. The different substitution pattern of the biaryls was used for tuning of emission maxima in the broad range of 366-565 nm. Using methods of computational chemistry the emission maxima were reproduced with a satisfactory degree of accuracy, and it was shown that the large solvatochromic shifts observed for the studied probes are proportional to the differences in dipole moments of the ground (S(0)) and excited (S(1)) states that add on top of smaller shifts predicted already for these systems in vacuo. Thus, we present a set of compounds that may serve as multipurpose base-discriminating fluorophores for sensing of hairpins, deletions, and mismatches by the change of emission maxima and intensities of fluorescence and that can be also conviently studied by (19)F NMR spectroscopy. In addition, aminobenzoxazolyl-fluorophenyl-labeled nucleotides and DNA also exert dual pH-sensitive and solvatochromic fluorescence, which may imply diverse applications.

π-Sufficient heteroaromatic compounds fused naphthalimide unit as novel solvatochromic fluorophores

The carbazoles 1 and dibenzofurans 2 having naphthalimide unit were synthesized by the cross coupling reaction of 4-bromonaphthalimide 3 with aniline and phenol derivatives followed by the intramolecular cyclization, respectively. The chromophores 1c and 2c substituted methoxy group exhibited the strong fluorescence solvatochromism.

High glass transition and thermally stable polynorbornenes containing fluorescent dipyrene moieties via ring-opening metathesis polymerization

A high-glass-transition-temperature polynorbornene, poly(NBEDPY), containing chromophore groups was synthesized by ring-opening metathesis polymerization (ROMP) using Grubbs' catalysts; poly(HNBEDPY) was obtained by the reduction of poly(NBEDPY). The glass transition temperatures (Tg) of poly(NBEDPY) and hydrogenated poly(HNBEDPY) were as high as 250 °C and 220 °C, respectively, because of the rigid dipyrene groups, which are higher than those of commercially available ring-opened hydrogenated polynorbornenes (JSR ARTON®; 120–165 °C). The 10% weight-loss temperatures of hydrogenated poly(HNBEDPY) and poly(NBEDPY) were up to 450 °C and 400 °C, respectively. A hydrogenated poly (HNBEDPY) film showed excellent transparency (over 91%). The photoluminescence emission spectra of poly(HNBEDPY) showed strong solvent-polarity dependence, revealing that poly (HNBEDPY) underwent remarkable bathochromic shifts with an increase in solvent polarity. Poly(HNBEDPY) also showed remarkable fluorescent solvatochromism (blue in toluene, greenish yellow in dimethyl sulfoxide). The cyclic voltammogram of poly(HNBEDPY) film cast onto an indium tin oxide (ITO)-coated glass substrate exhibited one reversible oxidation redox couple at 0.55 V versus Ag/Ag+ in acetonitrile solution. The electrochromic characteristics of poly(HNBEDPY) showed reversibility, with a color change from its green neutral form to dark red upon the application of potentials from 0 to 1.0 V. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Absorption and fluorescence of soluble polar diketo-pyrrolo-pyrroles

Six soluble derivatives of 3,6-diphenyl-2,5-dihydro-pyrrolo[3,4- c]pyrrole-1,4-dione N-alkylated on pyrrolinone ring with polar substituents in para positions of pendant phenyl rings were synthesized; five of them are reported for the first time. Absorption and fluorescence spectra were studied in solvents of different polarity. The compounds show small solvatochromism of absorption and a moderate positive solvatochromism of fluorescence, especially when substituted by strong electron-donating piperidino substituent. A significant decrease of fluorescence quantum yields and its biexponential decay for dipolar derivatives in polar solvents was tentatively ascribed to the formation of twisted intramolecular charge transfer (TICT) excited state. All six compounds show fluorescence in polycrystalline solid-state with the maxima covering a range over 200 nm in visible and near infrared region.

Facile and regioselective synthesis of poly(5-hydroxyquinoline)

The oxidative polymerization (OP) of unprotected 5-hydroxyquinoline (HQ) in an aqueous alkaline medium without an added external template, surfactants or functional dopants, leads to the formation of the C-3 and C-6 linked organic solvent-soluble, quinoline homopolymer (PHQ). The polymer had an average molecular weight of M n = 37,400 with a polydispersity index of 1.65. The fluorescence spectrum of PHQ exhibited an emission peak at approximately 500 nm in dimethyl sulfoxide (DMSO), which was nearly 118 nm red-shifted compared to the monomeric compound. In solution, PHQ showed fluorescence solvatochromism; it emitted blue light in tetrahydrofuran (THF) and green light in dimethylformamide (DMF) solutions with a relatively narrow full width of half maximum (FWHM). X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscope (AFM) analyses indicated that the resulting polymer was semicrystalline. Iodine doped-PHQ exhibited values of conductivity nearly 10 5 times higher compared to the undoped PHQ.

Temperature-Induced Self-Assembly of Triple-Responsive Triblock Copolymers in Aqueous Solutions

A series of triple-thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (PNPAM, A), poly(methoxydiethylene glycol acrylate) (PMDEGA, B), and poly(N-ethylacrylamide) (PNEAM, C) was synthesized by sequential reversible addition-fragmentation chain transfer polymerizations. Polymers of differing block sequences, ABC, BAC, and ACB, with increasing phase transition temperatures in the order A < B < C were prepared. Their aggregation behavior in dilute aqueous solution was investigated using dynamic light scattering, turbidimetry, and NMR spectroscopy. The self-organization of such polymers was found to dependent strongly on the block sequence. While polymers with a terminal low-LCST (lower critical solution temperature) block undergo aggregation above the first phase transition temperature at 20-25 °C, triblock copolymers with the low-LCST block in the middle show aggregation only above the second phase transition. The collapse of the middle block is not sufficient to induce aggregation but produces instead stable, unimolecular micelles with a collapsed middle block, as supported by NMR and fluorescence probe data. Continued heating of all copolymers led to two additional thermal transitions at 40-55 and 70-80 °C, which could be correlated to the phase transitions of the B and C blocks, respectively. All polymers show a high tendency for cluster formation, once aggregation is induced. The carrier abilities of the triple responsive triblock copolymers for hydrophobic agents were probed with the solvatochromic fluorescence dye Nile Red. With passing through the first thermal transition, the block copolymers are capable of solubilizing Nile Red. In the case of block copolymers with sequences ABC or ACB, which bear the low-LCST block at one terminus, notable amounts of dye are solubilized already at this stage. In contrast, the hydrophobic probe is much less efficiently incorporated by the BAC triblock copolymer, which forms unimolecular micelles. Only after the collapse of the B block, when reaching the second phase transition at about 45 °C, does aggregation occur and solubilization becomes efficient. In the case of ABC and ACB polymers, the hydrophobic probe seems to partition between the originally collapsed A chains and the additional hydrophobic chains formed after the collapse of the less hydrophobic B block.

Fluorescence Solvatochromism in Lumichrome and Excited-State Tautomerization: A Combined Experimental and DFT Study

Fluorescence solvatochromism of lumichrome (LC) was studied by steady-state and time-resolved fluorescence spectroscopy. The excited-state properties of LC do not show any correlation with solvent polarity, however, reasonably good correlation with solvent E(T)(30) parameter was observed. A quantitative estimation of contribution from different solvatochromic parameters, like solvent polarizability (π*), hydrogen bond donor (α), and hydrogen bond acceptor (β) ability of the solvent, was made using linear free energy relationship on the basis of Kamlet-Taft equation. The analysis reveals that hydrogen bond donating ability (acidity) of the solvent is the most important parameter that characterizes the excited-state behavior of lumichrome. Quantum mechanical calculations using density functional theory (DFT) were done to study the most stable structure and excited-state tautomerization process of LC toward the formation of isoalloxazines. Charge localization in the excited state and formation of hydrogen-bonded cluster through solvent hydrogen bond donation on the N10 atom of alloxazine moiety were predicted to be the key step toward this water-catalyzed tautomerization process.

Development of a quinoxaline-based fluorescent probe for quantitative estimation of protein binding site polarity

The compound 2-[(1E)-2-(1H-pyrrol-2-yl)ethenyl]-quinoxaline (PQX) is a promising fluorescent chromophore for the estimation of protein binding site polarity, due to its full-color solvatochromic fluorescence. A linear relationship was obtained between the peak emission wavenumber and E(T)(N) (normalized solvent polarity). The BSA binding site polarity was estimated from the solvatochromic plot.

Intensely blue-fluorescent 2,5-bis(benzoimidazol-2-yl)pyrazine dyes with improved solubility: their synthesis, fluorescent properties, and application as microenvironment polarity probes

Abstract In order to improve the solubility of intensively fluorescent 2,5-bis(benzimidazol-2-yl)pyrazine (BBIP), we synthesized new BBIP derivatives (2, 3a,b, and 5a,b) possessing two alkyl chains at the N-1 and N-1′ positions of the two benzimidazole moieties. Characterization of these compounds demonstrated that they exhibit high fluorescence intensity even in protic solvents, as well as solvatochromic fluorescence, in which their fluorescence maxima in aqueous methanol exhibited bathochromic shift with increasing ɛr value of the medium. We utilized 5a as a microenvironment polarity probe to indicate the variation in polarity around the backbone of the temperature-sensitive poly(N-isopropylacrylamide) by measuring the spectral change caused by the thermal phase transition of the polymer.

Chromotropic ferrocenyl chalcone with two pyrenyl groups: Solvatochromism and molecular chemosensor for Fe(III)/Fe(II) ions

Abstract A chromotropic ferrocenyl chalcone with two pyrenyl groups (Fc-dPyr) is prepared and spectroscopically characterized. The X-ray structure analysis shows that the two pyrenyl groups are almost parallel to each other with a torsion angle of 5.57° and adopt a dimeric mode with a distance of 3.776 A between them, ready to form an excimer. The solvatochromic fluorescence spectra indicate that the emission maxima observed in hydrogen-bonding donor (HBD) solvents (CHCl3, EtOH and MeOH) exhibit a strictly linear relationship with the normalized ETN value, while those in a non-HBD solvent (CH3CN) do not. The molecular chemosensor activity of Fc-dPyr is highly selective toward Fe(III) ions over Fe(II) ions. The fluorescence emission intensity of Fc-dPyr steeply decreases in the presence of Fe(III) ions as an oxidant, but not in the presence of Fe(II) ions.

Synthesis and Photophysical Properties of 2-Donor-7-acceptor-9-silafluorenes: Remarkable Fluorescence Solvatochromism and Highly Efficient Fluorescence in Doped Polymer Films

Recently, π-conjugated molecules containing a 9-silafluorene moiety have attracted considerable attention owing to their potential applications in organic electronics. While most studies focus on the oligomers and (co)polymers of 9-silafluorenes, functionalized 9-silafluorenes themselves remain unexplored. In this paper, we describe the preparation, photophysical properties, and theoretical calculations of 2-amino-7-acceptor-9-silafluorenes and we show that these silafluorenes can potentially be used as novel chromophores for functional organic materials. The D-π-A type silafluorenes were prepared by Pd-catalyzed intramolecular coupling of 2-(3-aminophenyldiisopropylsilyl)aryl triflates and the subsequent functional group conversion through reduction of the cyano group to a formyl and Knoevenagel condensation of the formyl group with malonitrile. The UV−visible absorption and fluorescence spectra of the D-π-A type silafluorenes exhibited a red-shift when the electron-withdrawing nature of the acceptor increased. The emission maxima of the fluorescence were highly dependent on the solvent. In the cases of formyl- and dicyanoethenyl-substituted silafluorenes, the emission colors ranged from blue to yellow for the formyl derivatives and from green to red for the dicyanoethenyl derivatives. The noticeable fluorescence solvatochromism suggests the intramolecular charge-transfer character of the excited states. The silafluorenes also exhibited fluorescence in the solid state (e.g., a neat thin film and a doped polymer film), and the emission color was dependent on the polarity of the polymer. In the solid state, the quantum yields of diphenylamino derivatives were generally higher than those of dimethylamino derivatives, presumably because the bulky diphenylamino group prevented chromophores from assembling close to each other. A comparison of the photophysical properties and theoretical calculations of D-π-A type silafluorenes with those of the corresponding fluorenes revealed that the silicon bridge contributed to the extension of the effective conjugation length of the biphenyl moiety when the acceptor was either hydrogen, trifluoromethyl, or a cyano group, whereas there was no contribution of the silicon bridge to the π-extension in silafluorenes substituted by strong electron acceptors such as formyl and dicyanoethenyl groups. White photoluminescence was demonstrated with an excellent quantum yield of 0.81 in the solid state from the poly(methyl methacrylate) (PMMA) film doped with Ph2N/CHO- and Ph2N/CH═(CN)2-substituted silafluorenes. This work reveals the potential of D-π-A type silafluorenes as versatile organic emitting materials.

Rodlike Fluorescent π-Conjugated 3,3′-Bipyridazine Ligand: Optical, Electronic, and Complexation Properties

We report on the design and synthesis of a new quadrupolar pi-conjugated 3,3'-bipyridazine D-A-D ligand. Its electronic and optical properties were investigated. Besides high fluorescence and pronounced solvatochromism, it exhibits an inherent electroactivity exploited to build an organic green light emitting device. Moreover, the ability of this ligand to complex metallic centers (Cu(I), Ni(II), Pt(II), and Ir(III)) was also investigated to access different geometries and to tune their electronic and optical properties. These preliminary results open up the synthesis of heavy-metal complexes to obtain phosphorescent emitters.