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Experimental and theoretical studies on the thermodynamics and properties of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates were undertaken by 1 H NMR measurements and DFT (density functional theory) calculations. The ratios of tautomers a / b of dihydropyrimidines (DPs) 1 , 2 , and 3 were determined under various conditions to reveal the effects of temperature, solvent, and concentration on the thermodynamic data. The observed results, the free energy differences (Δ G ), enthalpy differences (Δ H ), and entropy differences (Δ S ), are discussed in terms of the molecular structures, dipole moments (DM), and the electrostatic potential maps calculated by the DFT to clarify the nature of the DPs. [ABSTRACT FROM AUTHOR]

The substituent effect on optical properties of 3,14-diphenyl-17,17-di( n -pentyl)tetrabenzofluorene derivatives bearing electron-withdrawing groups (NC, CH 3 OCO, CH 3 SO 2 , and OHC) at 4-position of the phenyl groups were investigated. These compounds were readily prepared by using Suzuki–Miyaura cross-coupling as a key step. The 4-cyano, 4-methoxycarbonyl, and 4-methylsulfonyl derivatives display intense blue to blue-green fluorescence in CH 2 Cl 2 and in the solid states. On the other hand, the title compound forms two polymorphs, and thus, exhibit crystallochromism in fluorescence; the prismatic crystal emits intense yellow fluorescence, and the other crystal form does blue-green fluorescence. Moreover, the compound shows large solvatofluorochromism (Δ λ EM = 67 nm). The crystallographic analysis of the prismatic crystal reveals that the tetrabenzofluorene moiety of the compound possesses a helical structure with a C 2 symmetry and the molecules form a herringbone-like structure. The density function theory calculations predict the remarkable intramolecular charge-transfer character of the compound. The prediction is in good agreement with the observed fluorescence properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • A crystal of the [2.2]paracyclophane-containing organoboron complex shows PFC. • Inter- and intra-molecular π-stacking distances are reduced under high pressure. • The intermolecular π–π interaction is still the important factor leading to PFC. Piezofluorochromism (PFC) of crystals of a tert -butyl and [2.2]paracyclophane-containing diaroylmethanatoboron difluoride (p CP- t Bu), which is expected to possess both intermolecular and intra molecular π–π interactions, was investigated. p CP- t Bu crystals were found to exhibit remarkable PFC associated with an over 150-nm redshift of fluorescence (FL) wavelength occurring under increasing isotropic pressure applied by using a diamond anvil cell. X-ray crystallographic analysis showed that p CP- t Bu molecules in the crystal at atmospheric pressure exist in the form of an intermolecular π-stacking dimer through back-to-back π–π interactions. Moreover, the crystallographic data under high pressure showed that increasing isotropic pressure causes a reduction in both the intermolecular π-stacking distance of the dimer (D INTER) and the intra molecular π-stacking distance between two benzene rings in the [2.2]paracyclophane moiety (D INTRA). Density functional theory calculations, using the Cartesian coordinates obtained by X-ray analysis, suggest that the origin of PFC of p CP- t Bu crystals is the reduction of the LUMO energy of the π-stacking dimer and that the intermolecular π–π interaction is still the important factor leading to PFC of p CP- t Bu crystals. [ABSTRACT FROM AUTHOR]