Orthogonal Geometry Enhancing the Intersystem Crossing and Photosensitive Efficiency of Spiro Organoboron Compounds.

Based on the reported spiro organoboron compounds (PS1 and PS2 as potent 1O2 sensitizers), several new organoboron molecules (PS4-PS9) were constructed through structural modification, and their low-lying excited states and photophysical properties have been explored by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The predicted effective intersystem crossing (ISC) processes arise from the S1→T2 transition for PS4-PS6 and the S1→T4 transition for PS1, and corresponding KISC rate constants reach the order of magnitude of 109 (s-1). The organoboron compounds with a (N, N) chelate acceptor are predicted to exhibit relatively higher ISC efficiency than those bearing a (N, O) acceptor, and the planar C3NBN ring and the orthogonal configuration between the donor and acceptor moieties are responsible for the ISC rate enhancement. Importantly, the geometric features of the lowest singlet excited state (S1) for these compounds play a decisive role in their photosensitive efficiency. The present results provide a basis for better understanding of the photosensitivity of these spiro organoboron compounds and the structural modification effect.

Unraveling the structure-property relationship of novel thiophene and furan-fused cyclopentadienyl chromophores for nonlinear optical applications.

Development of organic nonlinear optical materials has become progressively more important due to their emerging applications in new-generation photonic devices. A novel series of chromophores based on innovative thiophene and furan-fused cyclopentadienyl bridge with various powerful donor and acceptor moieties were designed and theoretically investigated for applications in nonlinear optics. To unravel the structure-property relationship between this new push-pull conjugated systems and their nonlinear optical property, multiple methods, including density of states analysis, coupled perturbed Kohn-Sham (CPKS) method, sum-over-states (SOS) model, the two-level model (TSM), hyperpolarizability density analysis, and the (hyper)polarizability contribution decomposition, were performed to comprehensively investigated the nonlinear optical and electronic properties of this new π-system. Due to excellent charge transfer ability of new bridge and distinctive structure of donor and acceptor, the designed chromophores exhibit deep HOMO levels, low excitation energy, high dipole moment difference and large hyperpolarizability, indicating the appealing air-stable property and remarkable electrooptic performance of them. Importantly, THQ-CS-A3 and PA-CS-A3 shows outstanding NLO response properties with ßtot value of 6953.9 × 10-30 and 5066.0 × 10-30 esu in AN, respectively. The influence of the push-pull strength, the heterocycle and the π-conjugation of new bridge on the nonlinear optical properties of this novel powerful systems are clarified. This new series of chromophores exhibit remarkable electro-optical Pockels and optical rectification effect. More interestingly, PA-CS-A3 and THQ-CS-A2 also show appealing SHG effect. This study will help people understand the nature of nonlinear optical properties of innovative heteroarene-fused based cyclopentadienyl chromophores and offer guidance for the rational design of chromophores with outstanding electrooptic (EO) performance in the future.

Investigation of spectroscopic and electrical properties of doped poly(pyrrole-3-carboxylic acid).

The spectroscopic and electrical properties of poly(pyrrole-3-carboxylic acid) doped with p-TSA- (p-toluenesulfonate) and AQS- (anthraquinone sulfonate) were investigated. The variation in electrical conductivity as a function of temperature shows that the systems have semiconductor-like electrical characteristics. The investigated polymers exhibit 3D conductivity and less than 0.6 eV energy gaps. The IR and Raman spectra show that the charge carriers are polarons and bipolarons. Doping the poly(pyrrole-3-carboxylic acid) increases the number of charge carriers. Electron paramagnetic resonance has shown that localized polarons and bipolarons are formed within these polymers.

What Other Than Acridinium Esters? Computational Search for New Acridinium-Based Chemiluminogens.

The rapid increase in disease prevalence in the world makes it extremely important to search for new or develop existing diagnostic methods, for example, chemiluminescent labeling used in immunodiagnostics. At present, acridinium esters are willingly used as chemiluminogenic fragments of labels. However, the search for new chemiluminogens that are particularly efficient is the main task of our studies. The density functional theory (DFT) and time-dependent (TD) DFT methods were used to obtain thermodynamic and kinetic results concerning the chemiluminescence and competitive dark reactions, which indicated whether some of the scrutinized derivatives have better characteristics than the chemiluminogens used so far. Synthesis of these candidates for efficient chemiluminogens, followed by studies of their chemiluminescent properties, and ultimately in chemiluminescent labeling, are further steps to confirm their potential applicability in immunodiagnostics.

Solvent Effect on the Chemiluminescence of Acridinium Thioester: A Computational Study.

Chemiluminescent labelling, which is one of the promising procedures of modern immunodiagnostics, is increasingly carried out using acridinium derivatives, an oxidant, and an alkaline aqueous environment. However, the efficiency of the chemiluminescence of luminol or acridinium esters is higher in non-aqueous solvents such as dimethyl sulfoxide or acetonitrile. Therefore, the search for a new environment for the chemiluminescence reaction, especially the one characterized by a higher quantum yield of chemiluminescence, is one of the aims of current research. Using computational methods (DFT and TD DFT with PCM model of solvent), we examined thermodynamic and kinetic data concerning the chemiluminescence and competitive dark pathways. Our results suggest that better characteristics of the chemiluminescence reaction of acridinium thioester are observed in nonpolar solvents, such as methylcyclohexane, n-hexane and n-pentane, than in aqueous media used so far. Further experimental verification is necessary to confirm the possible application of proposed nonpolar solvents in chemiluminescent labelling and hence in immunodiagnostics.

Structure and IR Spectra of 3(5)-Aminopyrazoles and UV-Induced Tautomerization in Argon Matrix.

The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy difference: 10.7 kJ mol-1; Gibbs free energy difference: 9.8 kJ mol-1). The obtained matrix isolation IR spectra (in both argon and xenon matrices) were interpreted, and the observed bands were assigned to the tautomeric forms with help of vibrational calculations carried out at both harmonic and anharmonic levels. The matrix-isolated compound (in argon matrix) was then subjected to in situ broadband UV irradiation (λ > 235 nm), and the UV-induced transformations were followed by IR spectroscopy. Phototautomerization of the 3AP tautomer into the 5AP form was observed as the strongly prevalent reaction.

DFT and TD-DFT study on quadratic NLO response and optoelectronic activity in novel Y-shaped imidazole-based push-pull chromophores.

A theoretical analysis of a series of imidazole-based Y-shaped chromophores, D1-D8, is performed in order to investigate their non(linear) optical, fluorescence, and charge-transport properties. The calculations have been carried out employing DFT and TD-DFT methods at CAM-B3LYP and M06-2X levels of theory. FMO analysis reveals that in ground state, the highest occupied molecular orbital is localized on the 4,5-dimethylanilino donor moiety and imidazole core while the lowest unoccupied molecular orbital spreads on π-linker and nitro acceptor moieties. Vertical absorption and fluorescence transitions are characterized as intramolecular charge transfer and maximum absorption and fluorescence wavelengths show that by changing the π-bridge to the imidazole C2, we can tune fluorescence color from cyan to orange. Calculated (hyper)polarizabilities show that elongation of π-linker by polarizable subunits, such as double bonds or heteroaromatic rings, increases significantly the nonlinear response and shifts the charge-transfer band bathochromically. Calculated reorganization energies indicate that the studied compounds are hole-transporting materials rather than electron-transporters. Interestingly, D7 and D8, with higher hyperpolarizabilities, are predicted to be potent candidates for NLO-devices while D5 and D8 molecules are expected to be promising candidates for luminescent materials and good hole-transport materials for organic light-emitting diodes.

Spectral Probe for Electron Transfer and Addition Reactions of Azide Radicals with Substituted Quinoxalin-2-Ones in Aqueous Solutions.

The azide radical (N3●) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N3● reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N3● addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO4●-, CO3●-) and Tl2+ ions with the reduction potentials higher, and one radical (SCN)2●- with the reduction potential slightly lower than the reduction potential of N3● were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N3● with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N3● differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N3● is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N3● with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ)●+, radicals (7-R-3-MeQ)● and N3● adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning's aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions.

Computational Insights on the Mechanism of the Chemiluminescence Reaction of New Group of Chemiluminogens-10-Methyl-9-thiophenoxycarbonylacridinium Cations.

Immunodiagnostics, in which one of the promising procedures is the chemiluminescent labelling, is essential to facilitate the detection of infections in a human organism. One of the standards commonly used in luminometric assays is luminol, which characterized by low quantum yield in aqueous environments. Acridinium esters have better characteristics in this topic. Therefore, the search for new derivatives, especially those characterized by the higher quantum yield of chemiluminescence, is one of the aims of the research undertaken. Using the proposed mechanism of chemiluminescence, we examined the effect of replacing a single atom within a center of reaction on the efficient transformation of substrates into electronically excited products. The density functional theory (DFT) and time dependent (TD) DFT calculated thermodynamic and kinetic data concerning the chemiluminescence and competitive dark pathways suggests that some of the scrutinized derivatives have better characteristics than the chemiluminogens used so far. Synthesis of these candidates for efficient chemiluminogens, followed by studies of their chemiluminescent properties, and ultimately in chemiluminescent labelling, are further steps to confirm their potential applicability in immunodiagnostics.