LIF spectrum for the localised S0 → S1(ππ*) excitation in the H-bonded anthranilic acid dimer: Symmetry breaking or coupling of vibrations.

This study aims to investigate the impact of the π â†’ π* excitation localised in one monomer on the equilibrium geometry and oscillations of the AA dimer. Several low-frequency vibrations appear in pairs in the LIF spectrum because oscillations involving intermolecular hydrogen bonds are coupled, generating approximately symmetric and antisymmetric combinations (especially the COOH rocking modes, LIF: 295 and 301 cm-1). Furthermore, quantitative evaluation based on the TDDFT(B3LYP) results indicates that a dozen among 90 intramolecular oscillations are strongly coupled. In contrast, most vibrations are decoupled or weakly coupled, since they involve remote parts of the monomers. This makes several single vibrations active in the LIF spectrum (including the bending mode of the NH···O intramolecular hydrogen bond associated the strongest vibronic band 442 cm-1), while the other in each pair remains inactive. The reason for decoupling of oscillations and symmetry breaking is that the π â†’ π* electronic excitation is entirely localised within one of the monomers, which makes them no longer equivalent in terms of geometry and dynamics. Additionally, the excitation of one monomer induces strengthening and shortening by 6 pm of only one intermolecular hydrogen bond linking the carboxylic groups of both molecules. This causes the 1.7° in-plane distortion of the dimer and lowering of its symmetry to Cs group (from C2h for the S0 state). The distortion induces the activity of two low-frequency in-plane intermolecular vibrations, i.e. the geared oscillation (LIF: 58 cm-1) and the shearing motion (99 cm-1) of the monomers.

Photoinduced charge transfer in push-pull pyrazoline-based chromophores - Relationship between molecular structure and photophysical, photovoltaic properties.

The manuscript describes the effect of molecular structure on the photophysical and photovoltaic properties of the pyrazoline-based donor-branched-π-system-acceptor compounds decorated with two end groups: phenyl or thiophene. Although the absorption to the first singlet excited state is strongly allowed, the emission quantum yield is low in all studied solvents. This behaviour was explained by the existence of two non-radiative deactivation channels: the back electron transfer process, especially operated in polar solvents, and internal conversion realized as the rotation of flexible rotors (cyano, keto phenyl or thiophene). The feasibility of the photoinduced electron transfer process was corroborated by electrochemical, spectroelectrochemical measurements as well as DFT calculations. DFT calculations also support the existence of multiple conformations in the ground state, which differ from one another in terms of charge distribution and the values of ground state dipole moment. Finally, the mechanism of the singlet excited state deactivation of the studied compounds was determined by ultrafast pump-probe measurements. Our studies revealed that charge/electron transfer process may undergo over carbonyl bridge, included in branched π-system. Moreover, the thiophene decorated pyrazoline is characterized by a better photovoltaic power conversion efficiency, while the phenyl-ended pyrazoline can be applied as a viscosity sensor.

1H-Pyrazolo[3,4-b]quinolines: Synthesis and Properties over 100 Years of Research.

This paper summarises a little over 100 years of research on the synthesis and the photophysical and biological properties of 1H-pyrazolo[3,4-b]quinolines that was published in the years 1911-2021. The main methods of synthesis are described, which include Friedländer condensation, synthesis from anthranilic acid derivatives, multicomponent synthesis and others. The use of this class of compounds as potential fluorescent sensors and biologically active compounds is shown. This review intends to summarize the abovementioned aspects of 1H-pyrazolo[3,4-b]quinoline chemistry. Some of the results that are presented in this publication come from the laboratories of the authors of this review.

The Influence of Hydroponic Potato Plant Cultivation on Selected Properties of Starch Isolated from Its Tubers.

Starch is a natural polysaccharide for which the technological quality depends on the genetic basis of the plant and the environmental conditions of the cultivation. Growing plants under cover without soil has many advantages for controlling the above-mentioned conditions. The present research focuses on determining the effect of under cover hydroponic potato cultivation on the physicochemical properties of accumulated potato starch (PS). The plants were grown in the hydroponic system, with (greenhouse, GH) and without recirculation nutrient solution (foil tunnel, FT). The reference sample was PS isolated from plants grown in a tunnel in containers filled with mineral soil (SO). The influence of the cultivation method on the elemental composition of the starch molecules was noted. The cultivation method also influenced the protein and amylose content of the PS. Considering the chromatic parameters, PS-GH and PS-FT were brighter and whiter, with a tinge of blue, than PS-SO. PS-SO was also characterized by the largest average diameters of granules, while PS-GH had the lowest crystallinity. PS-SO showed a better resistance to the combined action of elevated temperature and shear force. There was a slight variation in the gelatinization temperature values. Additionally, significant differences for enthalpy and the retrogradation ratio were observed. The cultivation method did not influence the glass transition and melting.

1,3-Diphenyl-8-trifluoro-methyl-1H-pyrazolo-[3,4-b]quinoline.

The 1H-pyrazolo-[3,4-b]quinoline (PQ) core of the title mol-ecule, C(23)H(14)F(3)N(3), is aromatic and essentially planar (r.m.s. deviation = 0.015 Å) and the two phenyl substituents at positions 1 and 3 are twisted relative to this fragment by 29.74 (7) and 25.63 (7)°, respectively. In the crystal, mol-ecules are arranged along the b axis into stacks via π-π inter-actions, with an inter-planar distance of the PQ core of 3.489 (4) Å.

1,3,4-Triphenyl-7-trifluoromethyl-1H-pyrazolo[3,4-b]quinoline at 293 and 100 K.

In the structure of the title compound, C(29)H(18)F(3)N(3), belonging to the space group P6(5) (or P6(1)), three symmetry-independent molecules are arranged in two chains, with two molecules alternating along the 3(2) axes, whereas the remaining molecule forms a chain along [0001] due to the 6(5) screw axis. The conformation of each of the molecules is stabilized by an intramolecular C-H...N hydrogen bond, with C...N distances in the range 2.964 (6)-3.069 (5) A at room temperature (293 K) and 2.943 (4)-3.084 (4) A at low temperature (100 K). One molecule has its -CF(3) group ordered even at 293 K, which can be explained only by considering its involvement in two weak intermolecular C-H...F interactions, with C...F distances in the range 3.084 (6)-3.302 (5) A at 293 K and 3.070 (3)-3.196 (3) A at 100 K, and also a C-F...N interaction, with a C...N distance of 3.823 (5) A at 293 K and 3.722 (4) A at 100 K. The trifluoromethyl groups in the two remaining molecules are disordered at 293 K, whereas at 100 K the continuous (dynamic) positional disorder of one of the -CF(3) groups (of the molecule forming the chain along [0001]) is totally eliminated while the -CF(3) group disorder remains for the third molecule.

6-Fluoro-1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinoline benzene hemisolvate.

In the title compound, C(28)H(18)FN(3)·0.5C(6)H(6), the 1H-pyrazolo[3,4-b]quinoline core is almost planar (r.m.s = 0.0371 Å, maximum deviation = 0.0571 Å) and aromatic. The solvent benzene mol-ecules are located around inversion centres. In the crystal, mol-ecules related by centres of symmetry form dimers, with distances of 3.932 (3) Šbetween best planes through the fused core due to π⋯π stacking. The phenyl substituents at positions 1, 3 and 4, are twisted away from the core, making dihedral angles of 29.66 (7), 44.59 (7) and 67.94 (6)°, respectively.

3-Methyl-1,4-diphenyl-1H-pyrazolo-[3,4-b]quinoline.

In the title mol-ecule, C(23)H(17)N(3), the phenyl substituents at positions 1 and 4 are twisted relative to the central core by 27.09 (5) and 66.62 (4)°, respectively. In the crystal, mol-ecules are assembled into centrosymmetric dimers via π-π stacking inter-actions between the 1H-pyrazolo-[3,4-b]quinoline -units, with an inter-planar distance of 3.601 (2) Šand by weak inter-molecular C-H⋯N inter-actions.

2,7,12,17-Tttraoxa-3,4:5,6:13,14:15,16-tetrabenzodispiro[8.1.8.0]nonadecane.

The reaction of biphenyl-2,2'-diol with 1,1,2,2-tetrakis(bromomethyl)cyclopropane leads to two products, namely a propellane-type compound and a dispiro-type compound. The molecular structure of 4,5;6,7-dibenzo-3,8,12-trioxa[8.3.1]propellane has been determined previously by spectroscopic methods. The crystal structure of the dispiro product, 2,7,12,17-tetraoxa-3,4:5,6:13,14:15,16-tetrabenzodispiro[8.1.8.0]nonadecane, C(31)H(26)O(4), revealed that the conformations of the nine-membered heterocyclic rings are due to interactions between the pi-electron system of the biphenyl moiety and the lone electron pairs of the ether O atoms, the repulsion of the lone electron pairs of atoms O1...O2 and O3...O4, and steric interactions between H atoms in ortho positions. The conformations have C(1) symmetry and can be described approximately as twist-boat.