Tuning the Solid Phase Fluorescence Emission from Long Wavelength Visible to Near-Infrared in Oxazol-5-One Derivatives: Structure-Property Relationship, Theoretical and Experimental Studies.

Most of the fluorescent molecules among organic [Formula: see text]-conjugated materials show blue or green emission in the solid phase but few of them emit red-shifted visible and near-infrared light in the material science. To create molecules emitting for this feature, two π-conjugated oxazol-5-one derivatives containing donor (OCH3) and acceptor groups (NO2) were synthesized. Their optical and charge-transport properties were investigated through experimental and theoretical methods including the single crystal X-ray crystallography, Hirshfeld Surface Analysis, photophysical studies and Density Functional Theory (DFT), respectively. In addition, FT-IR, 1H-NMR, 13C-NMR spectroscopy, cyclic voltammetry (CV) measurements were performed. According to our results, both molecules may provide the significant pathway of development of long wavelength visible and red emissive features in solid phase with the aggregation induced enhanced emission (AIEE) properties particularly in the fields of OLEDs, optical communication, defence and bioimaging.

Synthesis and Characterization of Two Novel Oxazol-5-ones Derivatives and Their Multifunctional Properties; pH Sensitivity, Electropolymerizability and Antiproliferative Activity.

The aim of this study is to synthesize oxazol-5-one derivatives, which have multi-functional properties. Nomenclatures of newly synthesized molecules are 4-(4-N,N-diethylaminophenylmethylene)-2-(3-thienyl)oxazol-5-one (4a) and 4-(4-(1,4,7,10-tetraoxa-13-azacyclopentadecyl)phenylmethylene)-2-(3-thienyl)oxazol-5-one (4b). These two novel derivatives contain pH sensitive and polymerizable groups. 3-Thienyl group was attached to position-2 of the oxazol-5-one ring to provide electrochemical polymerization capability. pH sensing properties were provided by attaching p-N,N-diethylaminophenylmethylene and p-aza-15-crown-5-phenylmethylene groups to the arylmethylene moiety at position-4 of the ring. Target molecules were synthesized by classical process known as Erlenmeyer-Plöchl Azlactone Synthesis Erlenmeyer (Justus Liebigs Ann Chem 275:1-12, 1893), Rodrigues et al. (J Chem Educ 92:1543-1546, 2015) . After structural characterization of 4a and 4b, absorption and emission characteristics were determined in solvents that have different polarities. Difference in maximum absorption and emission wavelengths of the molecules related to solvent polarities were observed at around 6-7 nm and 35-36 nm respectively. In pH studies of the target derivatives in PVC polymer matrix, ratiometric changes were observed at isosbestic point around 398 nm. Polymeric depositions of the molecules (4a, 4b) were proved by using cyclic voltammetry, electrochemical impedance spectrometry studies and scanning electron microscope images. MTT assay studies showed significant results like, 4b derivative's strong cytotoxic activity on PC-3 (cancerous cell line) with IC50 value of 12.57 ± 0.41 µg/ml without exhibiting any cytotoxic effect on HEK293 (healthy cell line).

Synthesis, Spectroscopic Characterization and Polymerization Abilities of Blue and Green Light Emitting Oxazol-5-one Fluorophores.

New fluorescent thiophenyl group containing oxazol-5-one fluorophores of 3a (4-(3-thiophenylmethylene)-2-phenyloxazol-5-one), 3b (4-(3-thiophenylmethylene)-2-(4-tolyl)oxazol-5-one) and 3c (4-(3-thiophenylmethylene)-2-(4-nitrophenyl)oxazol-5-one) were synthesized and characterized. The newly synthesized oxazol-5-ones absorption and fluorescence characteristics were studied in some solvents of varying polarities. The heterocyclic chromophores were fluorescent, with two of them, 3a and 3b, emitting blue light, whilst the other one, 3c, emitting green light. The emission maxima of the derivatives varied between 415 and 572 nm according as the extent of conjugation and solvent polarity. As solvent polarity increased, 3c derivatives emission spectra displayed a large bathochromic shift, which revealed the considerable change of the dipole moment of the fluorescent structure because of an intramolecular charge transfer interaction. Furthermore, oxazolones polymerization ability via the thiophenyl group linked to the oxazol-5-one heterocycle showed that copolymerization of 3a was achieved, but homopolymerization was not observed.

Spectroscopic, Structural and Density Functional Theory (DFT) Studies of Two Oxazol-5-one Derivatives.

In this study, two oxazol-5-one derivatives, C20H20N2O2 (1) and C21H22N2O2 (2), were synthesized by getting condensed p-N,N-diethylaminobenzaldehyde with two presented hippuric acid derivatives and in further studies they were analysed spectrochemically. Molecular and crystal structures of the compounds were determined by single-crystal X-ray diffraction and the results revealed that the molecular packing of the crystal structures were stabilized by weak intraand intermolecular interactions also with C-O∙∙∙π, C-H∙∙∙π and π∙∙∙π stacking interactions. Computational studies were also performed using DFT method at B3LYP/6-311G(d,p) level of theory. Vibrational modes and chemical shifts were calculated and compared with the experimental data. In addition, frontier molecular orbitals and molecular electrostatic potential surfaces were simulated. The calculated results show that the optimized geometries can well reproduce the crystal structure. Purpose of this study was to survey the effects of the reactants, which were condensed with each other to produce oxazol-5-one, upon the characteristic properties and crystal forms of the final oxazol-5-one.

New Chromophore Systems from Coumarin-Oxazol-5-one Combination.

Coumarin-oxazol-5-one (COX), 3a-d, were synthesized with 7-methoxy-2-oxo-2H-chromene-4-carbaldehyde and benzoylglycine derivatives. The characterizations of the COX derivatives by 1H NMR, FT-IR and elemental analysis were achieved. To obtain the photophysical data of the synthesized COX derivatives were used spectrophotometric and spectrofluorimetric methods. Evaluation of the absorption and emission properties of the structures was carried out in six different solvents. Maximum absorption and emission wavelengths (λ; nm), molar extinction coefficients (ε; cm-1 M-1), Stoke's shifts (ΔλST; nm) and quantum yields (ϕF), of the COX derivatives were declared.

Spectrofluorimetric and Potentiometric Determination of Acidity Constants of 4-(4'-Acetyloxy-3'-Methoxybenzylidene)-5-Oxazolone Derivatives.

4-(4'-acetyloxy-3'-methoxybenzylidene)-5-oxazolone fluorescent molecules bearing four different aryl groups attached to the 2-position of 5-oxazolone ring have been investigated by spectrophotometric and potentiometric techniques in solution media. The acidity constants (pKa) of the fluorescent molecules were precisely determined in acetone, acetonitrile, dimethylformamide and in 1:1 mixture of toluene-isopropanol. The studied derivatives were titrated with tetrabutylammonium hydroxide and non-aqueous perchloric acid by scanning the basic and acidic region of the pH scale. A computerizable derivative method was used in order to descript precisely the end point and pKa values. The molecules investigated performed well-shaped and stoichiometric potentiometric titration curves.

Synthesis and Spectroscopic Studies of N,N'-dialkyl Derivatives of Antisymmetrical 2H,5H-Dihydropyrrolo[3,4-c]pyrrole-1,4-diones.

2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione derivatives (DPP) are chemically stable, fluorescent molecules, known as High Performance Pigments. Preparation of the soluble derivatives of DPPs provides great advantage in designing the optic sensor for new and existing applications and overcoming aggregation problems in solid matrices. For this purpose, the synthesis of antisymmetric DPPs and the formation of new organic dyes through N,N'-dialkylation and their spectroscopic studies have been carried out both in solutions and in solid phase.

Tuning photoinduced intramolecular electron transfer by electron accepting and donating substituents in oxazolones.

The solvatochromic and spectral properties of oxazolone derivatives in various solvents were reported. Fluorescence spectra clearly showed positive and negative solvatochromism depending on substituents. The solvatochromic plots and quantum chemical computations at DFT-B3LYP/6-31 + G(d,p) level were used to assess dipole moment changes between the ground and the first excited singlet-states. The electron accepting nitro substituent at the para-position increased the π-electron mobility, however, the 3,5-dinitro substituent decreased the π-electron mobility as a result of inverse accumulation of the electronic density as compared with that of its ground state. Experimental and computational studies proved that the photoinduced intramolecular electron transfer (PIET) is responsible for the observed solvatochromic effects. We demonstrate that PIET can be finely tailored by the position of the electron accepting and donating substituents in the phenyl ring of the oxazolone derivatives. We propose that the photoactive CPO derivatives are new molecular class of conjugated push-pull structures using azlactone moiety as the π-conjugated linker and may find applications in photovoltaic cells and light emitting diodes.

2-(Naphthalen-1-yl)-4-(naphthalen-1-yl-methyl-idene)-1,3-oxazol-5(4H)-one.

In the title compound, C(24)H(15)NO(2), the oxazole ring is oriented at dihedral angles of 10.09 (4) and 6.04 (4)° with respect to the mean planes of the naphthalene ring systems, while the two naphthalene ring systems make a dihedral angle of 4.32 (3)°. Intra-molecular C-H⋯N hydrogen bonds link the oxazole N atom to the naphthalene ring systems. In the crystal, inter-molecular weak C-H⋯O hydrogen bonds link the mol-ecules into centrosymmetric dimers. π-π contacts between the oxazole and naphthalene rings and between the naphthalene ring systems [centroid-centroid distances = 3.5947 (9) and 3.7981 (9) Å] may further stabilize the crystal structure. Three weak C-H⋯π inter-actions also occur.

2-(Naphthalen-1-yl)-4-(thio-phen-2-yl-methyl-idene)-1,3-oxazol-5(4H)-one.

The asymmetric unit of the title compound, C(18)H(11)NO(2)S, contains two crystallographically independent mol-ecules. In one mol-ecule, the oxazole and thio-phene rings are oriented at dihedral angles of 17.40 (9) and 18.18 (7)° with respect to the naphthalene ring system, while the oxazole and thio-phene rings are oriented to each other at a dihedral angle of 0.86 (9)°. In the other mol-ecule, the corresponding angles are 3.05 (8), 9.62 (6) and 7.02 (8)°, respectively. In each mol-ecule, a weak intra-molecular C-H⋯N hydrogen bond links the oxazole N atom to the naphthalene group. Weak inter-molecular C-H⋯O hydrogen bonding is present in the crystal structure. π-π stacking between the oxazole and thio-phene rings, between the thio-phene and naphthalene rings, and between the oxaozole and naphthalene rings, [centroid-centroid distances = 3.811 (2), 3.889 (2), 3.697 (2) and 3.525 (2) Å] may further stabilize the crystal structure.

Development of fluorescent array based on sol-gel/chitosan encapsulated acetylcholinesterase and pH sensitive oxazol-5-one derivative.

A highly sensitive fluorescent enzyme array for quantitative acetylcholine detection is developed. The enzyme array has been constructed by spotting of pH sensitive fluorophore 2-phenyl-4-[4-(1,4,7,10-tetraoxa-13-azacycloopentadecyl)benzylidene]oxazol-5-one and acetylcholinesterase doped in tetraethoxysilane/chitosan matrix via a microarrayer. The constructed tetraethoxysilane/chitosan network provided a microenvironment in which the enzyme molecule was active biologically. The optimal operational conditions for the array developed were investigated. The response of the developed biosensor array to acetylcholine was highly reproducible (RSD = 3.27%, n = 6). A good linearity was observed for acetylcholine in the concentrations up to 1 × 10(-8) M, with a detection limit of 0.27 × 10(-8) M.

2,5-Dihexyl-3,6-diphenyl-pyrrolo-[3,4-c]pyrrole-1,4(2H,5H)-dione.

The asymmetric unit of the title compound, C(30)H(36)N(2)O(2), contains one half-mol-ecule, the other half being generated by a crystallographic inversion centre. The crystal structure is devoid of any classical hydrogen bonds however, non-classical C-H⋯O inter-actions link the mol-ecules into chains propagating in [001] and a C-H⋯π inter-action leads to the formation of a two-dimensional network in (011).

Synthesis and spectroscopic studies of 3,6-diphenyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dion's N,N'-dialkyl derivatives.

3,6-diaryl-2,5-dihydro-1,4-diketopyrrolo[3,4-c]pyrrole-1,4-dione (DPPD) derivatives are used commercially as red pigments, because of their color strength, brightness, and very low solubility in most common solvents. These products, although highly colored, appear to be of limited value as dyes, since they show a tendency to form an aggregate when incorporated into a solvent. Monoalkyl and dialkyl derivatives of DPPD were synthesized and then characterized with IR, 1HNMR, UV-Vis absorption and emission spectroscopy. Molar absorption coefficient, singlet energy level and Stokes' shift values of DPPD derivatives were declared. Monoalkyl and dialkyl derivatives of DPPD's solubilities were measured from saturated solutions of dimethylformamide (DMF), tetrahydrofuran (THF), dichloromethane (DCM), acetonitrile (ACN) and toluene and they are compared with each other.

2-Methoxy-4-[(5-oxo-2-phenyl-4,5-dihydro-1,3-oxazol-4-ylidene)methyl]phenyl 4-methylbenzenesulfonate.

Molecules of the title compound, C(24)H(19)NO(6)S, adopt the Z configuration and have a distorted tetrahedral geometry around the S atom. The oxazolone, 2-phenyl and methoxyphenyl rings are approximately coplanar. The C atom between the methoxyphenyl and oxazolone rings displays a distorted trigonal bonding geometry. Pairs of molecules are linked into dimers through weak C-H...O hydrogen bonds.

Emission-based optical carbon dioxide sensing with HPTS in green chemistry reagents: room-temperature ionic liquids.

We describe the characterization of a new optical CO(2) sensor based on the change in the fluorescence signal intensity of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) in green chemistry reagents--room-temperature ionic liquids (RTILs). As far as we are aware, this is the first time RTILs, 1-methyl-3-butylimidazolium tetrafluoroborate (RTIL-I) and 1-methyl-3-butylimidazolium bromide (RTIL-II), have been used as matrix materials with HPTS in an optical CO(2) sensor. It should be noted that the solubility of CO(2) in water-miscible ionic liquids is approximately 10 to 20 times that in conventional solvents, polymer matrices, or water. The response of the sensor to gaseous and dissolved CO(2) has been evaluated. The luminescence intensity of HPTS at 519 and 521 nm decreased with the increasing concentrations of CO(2) by 90 and 75% in RTIL-I and RTIL-II, respectively. The response times of the sensing reagents were in the range 1-2 min for switching from nitrogen to CO(2), and 7-10 min for switching from CO(2) to nitrogen. The signal changes were fully reversible and no significant hysteresis was observed during the measurements. The stability of HPTS in RTILs was excellent and when stored in the ambient air of the laboratory there was no significant drift in signal intensity after 7 months. Our stability tests are still in progress.