Conformational isomerism

About: Conformational isomerism is a research topic. Over the lifetime, 11563 publications have been published within this topic receiving 199312 citations.

Synthesis and ion selectivity of all conformational isomers of tetrakis[(ethoxycarbonyl)methoxy]calix[4]arene

Abstract: We have found that the conformer distribution in tetra-O-alkylation of 5,11,17,23-tetra-tert-butylcalix[4]arene-25,26,27,28-tetrol by ethyl bromoacetate is remarkably affected by the metal cation present in the base. In general, the cone conformer predominantly results when the base contains template metal cations whereas the partial-cone and 1,3-alternate conformers result when the base contains nontemplate metal cations; in acetone solvent one can realize the change from the 100% cone selectivity to the 100% partial-cone selectivity. By combining the metal template effect with a protection-deprotection method with a benzyl group, we developed synthetic routes to all of the four conformers. Two-phase solvent extraction established that the cone conformer shows Na + selectivity whereas the remaininig three conformers show K + selectivity

Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters.

Abstract: Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two regioisomers of bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide, a donor–acceptor–donor (D–A–D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes.

A systematic investigation of factors influencing the decarboxylation of imidazolium carboxylates.

Abstract: A series of 1,3-disubstituted-2-imidazolium carboxylates, an adduct of CO2 and N-heterocyclic carbenes, were synthesized and characterized using single crystal X-ray, thermogravimetric, IR, and NMR analysis. The TGA analysis of the NHC-CO2’s shows that as steric bulk on the N-substituent increases, the ability of the NHC-CO2 to decarboxylate increases. The comparison of NHC-CO2’s with and without methyls at the 4,5-position indicate that extra electron density in the imidazolium ring enhances the stability of an NHC-CO2 thereby making it less prone to decarboxylation. Single crystal X-ray analysis shows that the torsional angle of the carboxylate group and the C−CO2 bond length with respect to the imidazolium ring is dependent on the steric bulk of the N-substituent. Rotamers in the unit cell of a single crystal of ItBuPrCO2 (2f) indicate that the C−CO2 bond length increases as the N-substituents rotate toward the carboxylate moiety, which suggests that rotation of the N-substituents through the plane of ...