Miguel Ponce-Vargas

Influence of the electron donor groups on the optical and electrochemical properties of borondifluoride complexes of curcuminoid derivatives: a joint theoretical and experimental study

Molecules displaying a p-conjugated D–A–D structure, in which D and A are electron donor and acceptor groups, respectively, represent an important class of dyes. In this work, we present a series of borondifluoride complexes of curcuminoid derivatives in which the central dioxaborine ring acts as a strong electron acceptor unit. Compounds 1–15 differ by the nature of the terminal D groups. We have also studied unsymmetrical compounds 16–23 that contain two different terminal donor groups, as well as compounds 24–32 in which an electron acceptor or donor unit has been introduced at the meso position of the dioxaborine ring. We describe the synthesis of the dyes that have not yet been reported in the literature, and report the electrochemical, absorption and fluorescence properties of all the compounds in dichloromethane. To gain insights into the electronic structures and optical properties, we performed DFT/TD-DFT calculations for a panel of representative compounds. We established correlations between the reduction potential and the Hammett s and s + constants, as well as between the redox gap and the emission wavelength. The electron donor character of one terminal D unit strongly influences (88 mV per unit of s) the reduction potential due to the strong resonance interaction along the curcuminoid backbone. The correlation points to the smaller effect of the meso substituent (50 mV per unit of s), which we relate to the twisted ground-state geometry of the meso aryl substituent. The correlation models established in this study may be useful to anticipate the optical and electrochemical properties of borondifluoride complexes of curcuminoids with good reliability.

Combined TD-DFT-SOS-CIS(D) Study of BOPHY Derivatives with Potential Application in Biosensing

A set of 13 bis(difluoroboron)-1,2-bis((pyrrol-2-yl)methylene)hydrazine (BOPHY) dyes is studied through a hybrid time-dependent density functional theory (TD-DFT)-scaled opposite spin-configuration interaction singles with a double correction [SOS-CIS(D)] approach accounting for solvent effects, to shed light onto the structure-property relationships of these recently developed chromophores. In the first step, we calculate the absorption-fluorescence crossing points with refined TD-DFT models considering the influences of both vibrational and solvent contributions. We found that the systematic overestimation of the 0-0 energies is effectively reduced by combining polarizable continuum model-TD-DFT with a scaled opposite spin-configuration interaction singles with a double correction [SOS-CIS(D)]. Next, for a representative system, the vibrationally resolved spectrum within the harmonic approximation is computed on the basis of TD-DFT vibrational signatures and an excellent match with experiment is found. Finally, the influence of different lateral groups on the spectroscopic properties is rationalized by investigating charge transfer parameters and examining electronic density difference maps. It is found that one can tune the position of the absorption/emission maxima by a judicious choice of the lateral substituents or by using π-extended segments. The largest absorption and emission wavelengths as well as the largest Stokes shifts are obtained for BOPHYs containing strong electron-donor dimethylaminophenyl groups attached to the α-positions of the pyrrole units through vinyl linkers, making these chromophores promising candidates for bioluminescence applications.

Metallacycles Capabilities in Host–Guest Chemistry

The perfect host for anions! The nature of host–guest interactions in metallacycle-based complexes was determined by various methodologies. Additionally, by plotting the atomic multipole moment tensors, a clear representation of the higher-order electrostatic interactions within the studied systems, such as dipole–quadrupole and quadrupole–quadrupole forces, was obtained.

Nature of Cucurbituril-Halogen Encapsulation. Structural and Interaction Energy Consideration in the X2@CB[n] (X=Cl, Br, I, n= 6, 7, 8) from Relativistic DFT calculations

The formation of host-guest species is a relevant issue in the obtaining of supramolecular arrays. In this work, the encapsulation of dihalogen molecules into different cucurbituril hosts allows further evaluation of the role of size and interaction energy for the stabilization of host-guest species. Our results for the X2@CB[n] (X = Cl, Br, I, n = 6, 7, 8) series, allow exploration of the hosts providing increasing cavity sizes, resulting in different host-guest scenarios. It is found that the interaction is mostly given by London type interactions (59% to 65%), followed by the electrostatic character of the interaction (31-27%). For species with a packing coefficient (PC) within the suggested favorable range (PC = 55-68%), and lower, the strength of the stabilizing electrostatic interaction and covalent character, and the repulsive Pauli term, remain similar. Moreover, the dispersion term varies to a large extent, owing to its relation to the available interacting internal face of CB[n], which is less in n = 7 and 8 counterparts. Hence, greater host flexibility is able to maximize the host-guest interactions, where this feature can be viewed as an interesting characteristic towards molecular recognition capabilities, which can be further studied in other related species such as cyclodextrins, pillararenes and other supramolecular hosts.