Molecular switch properties of 7‐hydroxyquinoline compounds

Abstract

The present study is concerned with the theoretical study of possible molecular switch systems. The 7-hydroxyquinoline-8-carboxamide molecule and its single-, double-, and triplesubstituted derivatives are investigated with the aim of revealing characteristic switch features. Molecular switches can be considered as composed of a frame and a crane component. According to a recent study, the 7-hydroxyquinoline doublering system constitutes the frame moiety, while a carboxamide group at position 8 plays the role of the crane part (Csehi et al., Phys. Chem. Chem. Phys. 2013, 15, 18048). The effect of single 2-,4-,6-methyl, double 2,4-, 2,6-diamino, and triple 2,4,6-triamino substitutions to the molecular frame has been investigated using high level ab initio techniques. As a possible reaction mechanism, excited state intramolecular hydrogen transfer mediated by the frame-crane torsion has been considered. At the terminal structures of this pathway, second-order approximate coupled-cluster (CC2) quality vertical excitation energies and oscillator strengths have been calculated for the three lowest-lying singlet electronic excited states of all the studied systems. Single point calculations at selected geometries of the reaction path were carried out at the CC2 level as well, while conical intersections (CIs) between the ground and first excited states near perpendicular twisted geometries were optimized using the complete active space self-consistent field method. To confirm the presence of CIs, nonadiabatic coupling terms have been derived and applying the topological line integral technique, the topological (or Berry) phase has been calculated surrounding the point of CI. The results of this work clearly demonstrate the fulfillment of several molecular switch properties by the investigated quinoline derivatives. An extensive comparison between the different compounds is presented as well.

Description of spin–orbit coupling in excited states with two-component methods based on approximate coupled-cluster theory

“…First applications showed no significant difference between the results obtained with CC2 and ADC (2). The computed excitation energies and the resulting zero-field splittings are in reasonable agreement with experiment.…”

Long-Range Proton Transfer in 7-Hydroxy-Quinoline-Based Azomethine Dyes: A Hidden Reason for the Low Efficiency

“…In most of the photo switchable molecules based on 7HQ, studied so far [ 5 , 19 , 20 , 21 ], the ESIPT process from the initially photoexcited enol form towards the nitrogen atom in the proton crane to form proton-transferred K E (S 1 ) tautomer was considered as a dominating channel. However, the presence of the double C=N bond in the azomethine craning group gives a possibility of an additional geometrical transformation in the molecule, namely trans – cis photoisomerization.…”

“…The enol tautomer is substantially more stable, while the NH tautomer has been experimentally observed only in protic organic solvents or in the presence of water and results from the intermolecular, solvent-assisted PT mechanism [ 17 , 18 ]. Previous computational studies of the potential energy profiles along the relevant internal coordinates, such as the O–H and N–H bond stretching distances, suggested that forward and backward PT process could be observed for a series of molecules containing 7HQ , as a general tautomeric frame for the location of the O and N atoms in the space, and oxazine [ 5 , 19 ], other six-membered ring heterocycles [ 19 ], pyridines [ 19 ], carbaldehyde groups [ 18 ], and CO-BF 2 [ 20 , 21 ] as proton cranes. Among them, the smallest in size, the carbaldehyde moiety, seemed to be a reasonably good choice allowing for fast rotation even when protonated [ 18 , 22 ].…”

Blockade of persistent colored isomer formation in photochromic 3H-naphthopyrans by excited-state intramolecular proton transfer

“…The ESIPT phenomenon was utilized as a photoswitching mechanism in internally hydrogen-bonded molecules 17 – 19 . The search for proton cranes, in which a proton can be transferred over long distances through large-amplitude motion, is still a hot topic 20 – 22 .…”