Optimized deep CNN for detection and classification of diabetic retinopathy and diabetic macular edema.

Diabetic Retinopathy (DR) and Diabetic Macular Edema (DME) are vision related complications prominently found in diabetic patients. The early identification of DR/DME grades facilitates the devising of an appropriate treatment plan, which ultimately prevents the probability of visual impairment in more than 90% of diabetic patients. Thereby, an automatic DR/DME grade detection approach is proposed in this work by utilizing image processing. In this work, the retinal fundus image provided as input is pre-processed using Discrete Wavelet Transform (DWT) with the aim of enhancing its visual quality. The precise detection of DR/DME is supported further with the application of suitable Artificial Neural Network (ANN) based segmentation technique. The segmented images are subsequently subjected to feature extraction using Adaptive Gabor Filter (AGF) and the feature selection using Random Forest (RF) technique. The former has excellent retinal vein recognition capability, while the latter has exceptional generalization capability. The RF approach also assists with the improvement of classification accuracy of Deep Convolutional Neural Network (CNN) classifier. Moreover, Chicken Swarm Algorithm (CSA) is used for further enhancing the classifier performance by optimizing the weights of both convolution and fully connected layer. The entire approach is validated for its accuracy in determination of grades of DR/DME using MATLAB software. The proposed DR/DME grade detection approach displays an excellent accuracy of 97.91%.

Multiple linear regression solvatochromic analysis of donar-acceptor imidazole derivatives.

Catalytic synthesis of some polysubstituted imidazoles under solvent-free condition is reported and their characterization has been carried out spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends both the polarity of the medium and hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on absorption and emission spectral results has been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazoles fit satisfactorily to a bi exponential kinetics. These observations are in consistent with quantum chemical calculations.

Photoinduced electron transfer from phenanthrimidazole to magnetic nanoparticles.

The dynamics of photoinduced electron injection from (E)-1-(4-methoxyphenyl)-2-styryl-1H-phenanthro [9,10-d]imidazole (MPSPI) synthesised using nano TiO(2) as catalyst to Fe(2)O(3) nanocrystal has been studied by FT-IR, absorption, fluorescence and lifetime spectroscopic methods. The binding between nanoparticle and MPSPI is confirmed by binding constant and binding site. The distance between MPSPI and nanoparticle as well as the critical energy transfer distance has been obtained. The free energy change (ΔG(et)) for electron injection has also been deduced.

Excited Charge Transfer States in Donor-Acceptor Fluorescent Phenanthroimidazole Derivatives.

Solvent-dependent electronic structure of the selected donor (D) acceptor (A) derivatives of phenanthroimidazole derivatives containing fluoro substituent as an electron acceptor fragment in the fluorescent charge transfer (CT) states has been investigated. The mechanism of the radiative charge recombination CT → S0 is discussed in terms of the Mulliken-Murrell model of the CT complexes and the Marcus theory of photoinduced electron transfer (ET). Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all of the compounds studied both in a polar and a non polar environment. An analysis of the CT fluorescence leads to the quantities relevant for the electron transfer in the Marcus inverted region. The values of the fluorescence rate constants (k r ) and corresponding transition dipole moments (M) and their solvent polarity dependence indicate that the electronic coupling between the emitting (1)CT state and the ground state is a governing factor of the radiative transitions. The relatively large values of M indicate a nonorthogonal geometry of the donor and acceptor subunits in the fluorescent states. It is shown that Marcus theory can be applied for the quantitative description of the radiationless charge recombination processes in the cases when an intersystem crossing to the excited triplet states can be neglected.

Estimation of Excited State Dipolemoments from Solvatochromic Shifts-Effect of pH.

Multicomponent, highly efficient, catalytic synthesis of some polysubstituted imidazole under solvent-free condition is reported. Characterization of polysubstituted imidazole have been carried out by X-ray diffraction (XRD) and spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on both the absorption and emission spectral results have been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazole fit satisfactorily to a single exponential kinetics. The prototropic studies of N,N-dimethyl-4-(1,4,5-triphenyl-1H-imidazol-2-yl)naphthalen-1-amine (DTINA) reveal that two monocations [imidazole nitrogen protanated (MC1) and dimethylamino nitrogen protanated (MC2)] and a dication [both imidazole nitrogen and dimethylamino nitrogen protanated (DC)] are formed by protonation in both ground and excited states. These observations are in consistent with quantum chemical calculations.

Dynamics of Solvent Controlled ESIPT of π-Expanded Imidazole Derivatives - pH Effect.

A set of π-expanded imidazole derivatives employing excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The relationship between the structure and photophysical properties were thoroughly elucidated by comparing with the analogue blocked with ESIPT functionality. The compound possessing an acidic NH function as part of an intramolecular hydrogen bond system has much higher fluorescence quantum yield and Stokes shift and the π-expansion strongly influences the optical properties. The occurrence of ESIPT for imidazole tosylamide derivatives were less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amine. The low pKa values for the monocation ⇌ neutral equilibrium indicate the presence of intramolecular hydrogen bonding between the amino proton and tertiary nitrogen atom.

Sensitive and selective PET-based π-expanded phenanthrimidazole luminophore for Zn2+ ion.

The novel photoinduced electron transfer (PET) chemosensor, 1-(1-(4-methoxyphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [MPPN] and its zinc complex were synthesised and characterized by electronic spectral and Frontier molecular orbital energy analysis. MPPN becomes efficient fluorescent chemosensor upon binding with metal ions and shows a strong preference toward Zn(2+) ion. Density Functional theory (DFT) calculations reveal that luminescence of free MPPN originates from its orbital structure in which two π-orbitals (HOMO and HOMO-1) of the imidazole ring are situated between two π-orbitals (HOMO-2 and LUMO) of the naphthyl fragment. Therefore the absorption and emission processes occur between the two π- orbitals (HOMO-2 and LUMO). The two higher energy imidazole orbitals (HOMO and HOMO-1) serve as quenchers for the excited state of the molecule through nonradiative processes. Upon binding with Zn(2+) ion, MPPN becomes a highly luminescent with λemi - 421 nm. The significant enhancement of luminescence upon binding with Zn(2+) ion is attributed to the stabilization of HOMO-2 and HOMO-1 π-orbitals of imidazole ring upon their engagement in new bonds with Zn(2+) ion. The affinity of MPPN to zinc ion is found to be very high [K = 6 × 10(6) M(-1)] when compared with other metals ions. The nonlinear absorption coefficient γ for MPPN is 1.9 × 10(-12) m/W and 3.9 × 10(-11) m/W for MPPN-Zn complex.

Photoinduced intramolecular electron transfer and electronic coupling interactions in π- expanded imidazole derivatives.

An intramolecular excited charge transfer (CT) analysis of imidazole derivatives has been made. The determined electronic transition dipole moments has been used to estimate the electronic coupling interactions between the excited charge transfer singlet state ((1)CT) and the ground state (S0) or the locally excited state ((1)LE). The properties of excited (1)CT state imidazole derivatives have been exploited by the significant contribution of the electronic coupling interactions. The excited state intramolecular proton transfer (ESIPT) analysis has also been discussed.

Radiative and nonradioactive electron transfer in donor-acceptor phenanthrimidazoles.

Photoinduced electron transfer in a series of naphthyl substituted phenanthrimidazoles has been studied in solutions. The intramolecular charge transfer (CT) leads to a large Stokes shift and large dipole moment in the fluorescent state. Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all the compounds studied. An analysis of the CT fluorescence lead to the quantities relevant for the electron transfer in the Marcus inverted region.

Structural, Electronic and Charge Transfer Studies of Highly Sensitive Fluorescent Probe 2-((E)-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenol: Quantum Chemical Investigations.

This article presents a facile synthesis of novel class of bluish-green fluorescent 2-((E)-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenol [PPIVP] and their optical, electrochemical and thermal properties. Detailed photophysical and quantum chemical studies have been performed to elucidate the origin of the dual emission shifts. PPIVP undergo excited state intramolecular proton transfer (ESIPT) reaction leading a large Stoke's shifted fluorescence emission from the phototautomer. The results of quantum chemical investigations not only confirmed the intramolecular charge transfer characteristics of the ESIPT tautomers but also provided a rational for the observed high fluorescence quantum efficiency in the solid state. The high photoluminescence quantum yield in the solid state is ascribed to twisted chromophores due to phenyl substituents at 1,2-position of the phenanthroimidazole ring which restricted intramolecular motion, leading to an optically allowed lowest optical transition without self quenching.

Tuning Photophysical and Electrochemical Properties of Phosphorescent Heteroleptic Iridium Complex Salts-as Chemosensors.

Photophysical and electrochemical studies of cyclometalated cationic heteroleptic iridium(III) complex salts have been carried out. For these complex salts the intense absorption bands appeared around 263 nm and are assigned to spin-allowed π-π* transitions of phenanthroline ligands. Moderately intense and weak absorption bands observed around 341 and 440 nm, respectively. These bands are assigned to spin-allowed metal to ligand charge transfer (1)MLCT and (3)MLCT transitions, respectively. The influence of anions and proton on the photophysical and electrochemical studies were also carried out. The emission wavelength was red shifted and emission color changed from yellow to red by the addition of CF3CO2H. The solution color changed from green to brown and the emission was quenched by the addition anions such as of F(-), CH3COO(-) and H2PO4(-).

Spectroscopic studies on photoelectron transfer from 2-(furan-2-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole to ZnO, Cu-doped ZnO and Ag-doped ZnO.

The 2-(furan-2-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole [FPI] has been designed and synthesized as fluorescent sensor for nanoparticulate ZnO. The present work investigates the photoelectron transfer (PET) from FPI to ZnO, Cu-doped ZnO and Ag- doped ZnO nanoparticles using electronic and life time spectral measurements. Broad absorption along with red shift indicates the formation of charge-transfer complex [FPI-Nanoparticles]. The photophysical studies indicate lowering of HOMO and LUMO energy levels of FPI on adsorption on ZnO due to FPI- ZnO interaction. The obtained binding constant implies that the binding of FPI with nanoparticles was influenced by the surface modification of ZnO nanoparticles with Cu and Ag.

Crystal structures of (E)-(3-ethyl-1-methyl-2,6-di-phenyl-piperidin-4-yl-idene)amino phenyl carbonate and (E)-(3-isopropyl-1-methyl-2,6-di-phenyl-piperidin-4-yl-idene)amino phenyl carbonate.

In the title compounds, C27H28N2O3, (I), and C28H30N2O3, (II), the conformation about the C=N bond is E. The piperidine rings adopt chair conformations with the attached phenyl rings almost normal to their mean planes, the dihedral angles being 85.82 (8) and 85.84 (7)° in (I), and 87.98 (12) and 86.42 (13)° in (II). The phenyl rings are inclined to one another by 52.87 (8)° in (I) and by 60.51 (14)° in (II). The main difference in the conformation of the two compounds is the angle of inclination of the phen-oxy-carbonyl ring to the piperidine ring mean plane. In (I), these two planes are almost coplanar, with a dihedral angle of 2.05 (8)°, while in (II), this angle is 45.24 (13)°. In the crystal of (I), mol-ecules are linked by C-H⋯O hydrogen bonds, forming inversion dimers with R 2 (2)(14) loops. The dimers are linked via C-H⋯π inter-actions forming a three-dimensional network. In the crystal of (II), there are no significant inter-molecular inter-actions present.

(E)-3-Methyl-2,6-di-phenyl-piperidin-4-one O-(3-methyl-benzo-yl)oxime.

In the title compound, C26H26N2O2, the piperidine ring exhibits a chair conformation. The phenyl rings are attached to the central heterocycle in an equatorial position. The dihedral angle between the planes of the phenyl rings is 57.58 (8)°. In the crystal, C-H⋯O inter-actions connect the mol-ecules into zigzag chains along [001].

(E)-3-Isopropyl-1-methyl-2,6-di-phenyl-piperidin-4-one O-nicotinoyl oxime.

In the title compound, C27H29N3O2, the piperidine ring exists in a chair conformation with an equatorial orientation of the phenyl and methyl substituents. The C-C=N bond angles are significantly different [119.1 (2) and 127.2 (2)°]. The phenyl rings are inclined to one another by 44.90 (14)°, and by 80.85 (13) and 79.62 (12)° to the mean plane of the piperidine ring. The terminal pyridine ring is inclined to the piperidine ring mean plane by 74.79 (15)°. In the crystal, mol-ecules are linked by C-H⋯π inter-actions, forming a three-dimensional network.

(E)-1,3-Dimethyl-2,6-di-phenyl-piperidin-4-one O-(phen-oxy-carbon-yl)oxime.

The title piperidine derivative, C26H26N2O3, has an E conformation about the N=C bond. The piperidine ring has a chair conformation and its mean plane is almost perpendicular to the attached phenyl rings, making dihedral angles of 87.47 (9) and 87.34 (8)°. The planes of these two phenyl rings are inclined to one another by 60.38 (9)°. The plane of the terminal phenyl ring is tilted at an angle of 32.79 (9)° to the mean plane of the piperidine ring. The mol-ecular conformation is stabilized by two intra-molecular C-H⋯O contacts. There are no significant inter-molecular inter-actions in the crystal.

Synthesis of some fluorescent benzimidazole derivatives using cobalt(II) hydroxide as highly efficient catalyst--spectral and physico-chemical studies and ESIPT process.

Some fluorescent benzimidazole derivatives have been designed and synthesized using cobalt(ii) hydroxide as highly efficient catalyst. Synthesized compounds have been characterized by (1)H and (13)C-NMR and mass spectral analysis. The solvent effect on the absorption and fluorescence bands has been analyzed and supplemented by computational studies. Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the charge transfer (CT) character of the emitting singlet states of all of the compounds studied in both polar and non-polar environments. The fluorescence decays for the benzimidazoles fit satisfactorily to a single exponential kinetics. HOMO and LUMO orbital pictures [DFT/B3LYP/6-31G(d,p)] evidence the existence of excited state intramolecular proton transfer (ESIPT) in benzimidazole derivatives containing a hydroxy group.

[(4E)-1-Methyl-2,6-diphenyl-3-(propan-2-yl)piperidin-4-yl-idene]amino 3-methyl-benzoate.

In the title compound, C29H32N2O2, the piperidine ring exists in a chair conformation (the bond-angle sum at the sp (2)-hybridized C atom is 359.79°). The phenyl rings and the methyl group substituted on the heterocyclic ring are in equatorial orientations. In the crystal, pairs of C-H⋯π inter-actions result in the formation of inversion dimers.

[(4E)-3-Ethyl-1-methyl-2,6-di-phenyl-piperidin-4-yl-idene]amino 3-methyl-benzoate.

In the title compound, C28H30N2O2, the piperidine ring exists in a chair conformation with an equatorial orientation of the phenyl rings and methyl group substituted on the heterocycle. In the crystal, C-H⋯π inter-actions result in chains of mol-ecules running parallel to the a-axis direction.

Kamlet-taft and Catalan studies of some novel Y-shaped imidazole derivatives.

Some novel Y-shaped imidazole derivatives were developed and characterized by NMR and mass spectral techniques. The photophysical properties of these imidazole derivatives were studied in several solvents. The Kamlet-Taft and Catalan's solvent scales were found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The adjusted coefficient representing the electron releasing ability or basicity of the solvent, C(ß) or C(SB) has a negative value, suggesting that the absorption and fluorescence bands shift to lower energies with the increasing electron-donating ability of the solvent. This effect can be interpreted in terms of the stabilization of the resonance structures of the chromophore. The observed lower fluorescence quantum yield may be due to an increase in the non-radiative deactivation rate constant. This is attributed to the loss of planarity in the excited state provided by the non co-planarity of the cinnamaldehyde ring attached to C(2) atom of the imidazole ring. Such a geometrical change in the excited state leads to an important Stokes shift, reducing the reabsorption and reemission effects in the detected emission in highly concentrated solutions.