The crystal and molecular structures of two new phosphorochromones determined by single-crystal X-ray diffraction are presented. The existence of two tautomers stabilized by intramolecular N−H···O and O−H···N hydrogen bonds and environmental effects in crystals is observed as evidence of the proton transfer reaction. The proton transfer process within simple enaminones being analogues of the compounds studied by X-ray diffraction methods is investigated usingMP2/6-311++G** and MP4/6-311++G** levels of theory. The Bader theory is also applied in the analysis of the hydrogen bonding within investigated systems. The results indicate that the systems with N−H···O intramolecular hydrogen bonds are more stable than those containing O−H···N bonds.

In the current work, comprehensive photophysical and electrochemical studies were performed for eight rhenium(I) complexes incorporating 2,2′:6′,2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine (dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and 1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally affected the energy of the MLCT absorption and emission bands, signaling a weak electronic coupling of the appended aryl group with the Re(I) center. The triplet MLCT state in these complexes is so low lying relative to the triplet 3 IL aryl that the thermal population of the triplet excited state delocalized on the organic chromophore is ineffective. The attachment of the electron-rich pyrenyl group resulted in a noticeable red shift and a significant increase in molar absorption coefficients of the lowest energy absorption of the resulting Re(I) complexes due to the contribution of intraligand charge-transfer (ILCT) transitions occurring from the pyrenyl substituent to the terpy/dppy core. At 77 K, the excited states of [ReCl(CO) 3 (L n -κ 2 N )] with 1-pyrenyl-functionalized ligands were found to have predominant 3 IL pyrene / 3 ILCT pyrene→terpy character. The 3 IL/ 3 ILCT nature of the lowest energy excited state of [ReCl(CO) 3 (4′-(1-pyrenyl)-terpy-κ 2 N )] was also evidenced by nanosecond transient absorption and time-resolved emission spectroscopy. Enhanced room-temperature emission lifetimes of the complexes [ReCl(CO) 3 (L n -κ 2 N )] with 1-pyrenyl-substituted ligands are indicative of the thermal activation between 3 MLCT and 3 IL/ 3 ILCT excited states. Deactivation pathways occurring upon light excitation in [ReCl(CO) 3 (4′-(1-naphthyl)-terpy-κ 2 N )] and [ReCl(CO) 3 (4′-(1-pyrenyl)-terpy-κ 2 N )] were determined by femtosecond transient absorption studies.

Six compounds containing N-methylpyrazoline ring fused with flavanone derivatives have been synthesized and characterized by X-ray structural studies and fluorescence spectroscopy. The influence of molecular arrangement on the emission properties, including fluorescence lifetime and quantum yield, was discussed on the basis of structural data and detailed analysis of the Hirshfeld surfaces. The correlation of fluorescence and crystal packing reveals that 1 solid state emission of this class of compounds strongly depends on intermolecular interactions present in different crystal lattice. It was observed that the inverse of fluorescence lifetime (1/τavg)is linearly dependent on a percentage contribution of H…O and H…N contacts in the Hirshfeld surface. In addition, the lipophilicity (log P) of these compounds is related to contribution of C…H interactions as well as non-covalent bonding involving a halogen atom.

Intramolecular N-H...O hydrogen bonds in 3-(aminomethylene)pyran-2,4-dione and its simple derivatives (F, Li, and BeH substituents) were analyzed theoretically. The systems were optimized at the B3LYP/6-311++G(d,p) level of approximation. For some fluorine derivatives the corresponding tautomers with O-H...N intramolecular H-bonds were investigated, and for such pairs of tautomers, the calculations on transition states of the N-H...O <--> N...H-O proton-transfer reaction were carried out. The geometrical and energetic parameters for these species were characterized. The topological parameters derived from Bader theory were also analyzed; these are characteristics of H-bond critical points and also of ring critical points. Besides N-H...O and O-H...N intramolecular hydrogen bonds, there are the other intramolecular interactions, mostly ionic such as Be(+delta)...(-delta)O, Li(+delta)...(-delta)O, and Li(+delta)...(-delta)F. The F...O interactions also exist for some of species investigated. They may be classified as energetically stabilizing ones since the corresponding bond paths and critical points exist. The numerous correlations and dependencies between geometrical, topological, and energetic parameters were detected and described.