Abstract:Der lichtinduzierte Farbwechsel chemischer Verbindungen, die Photochromie, ist ein Gebiet hoher Aktualitat. Zahlreichemeist monomolekulare -Reaktionen wurden unter diesem Aspekt genauer untersucht. Photochromes Verhalten organischer Verbindungen beruht vorzugsweise auf cis-frans-Isomerisierungen und pericyclischen Reaktionen sowie Tautomerisierungs-und Dissoziationsprozessen. In dieser Gruppe nehmen die elektrocyclischen Reaktionen wohl den bedeutendsten Platz ein. Als vielversprechende neue Systeme mit hoher … Show more
“…Conversion of the cis -MC to SP in solvents where the quinoidal form of the MC predominates can be formulated as an intramolecular electrocyclic process via the transition state ( TS *) . These types of reactions do not have an appreciable solvent dependency associated with them, which argues against this being the rate-determining step (RDS), noting the marked solvent effect which is observed on the rate of ring closure. …”
In continuing studies of the effect of solvent and molecular structure on the behavior of photochromic and thermochromic dye molecules, especially spiropyran (SP)-merocyanine (MC) interconversions, we have examined a series of 6′-nitrobenzoindolinospiropyrans (6-nitro-BIPS) with varying N-functionalities (R ) CH 3 , CH 2 CH 2 COOH, CH 2 CH 2 CH 2 SO 3 -, CH 2 CH 2 COO-Cholesteryl). The solvent effect was assessed by following the thermal decay of the photochemically ring-opened merocyanine to the spiropyran (MC H SP) via UV/vis spectroscopy at the λ max of the MC form. It was found that while modification of the N-moiety produced no perturbations in the solvatochromic behavior of these dyes, there was a marked effect on the solvatokinetic behavior. In nonpolar solvents, where the MCs possess predominantly quinoid character (unit central bond order), a constant thermal reversion rate was observed for the MCs with electron-rich N-ligands. This was attributed to electronic and steric interactions between the ligands and the phenoxide moiety. However, in polar solvents the increased zwitterionic character of the MCs (central bond order ∼2) leads to inhibition of the thermal reversion rate for the MCs in this study, independent of N-functionality. The MC H SP interconversion has also been examined by means of semiempirical calculations. These reveal the lowest energy pathway for conversion of the trans-MC to a cis-MC form via sequential bond rotation of the three central dihedral angles (R, β, and γ). The calculations support the observed solvatokinetic behavior, leading to the assignment of the trans/cis thermal isomerization as the rate-determining step in the overall process.
“…Conversion of the cis -MC to SP in solvents where the quinoidal form of the MC predominates can be formulated as an intramolecular electrocyclic process via the transition state ( TS *) . These types of reactions do not have an appreciable solvent dependency associated with them, which argues against this being the rate-determining step (RDS), noting the marked solvent effect which is observed on the rate of ring closure. …”
In continuing studies of the effect of solvent and molecular structure on the behavior of photochromic and thermochromic dye molecules, especially spiropyran (SP)-merocyanine (MC) interconversions, we have examined a series of 6′-nitrobenzoindolinospiropyrans (6-nitro-BIPS) with varying N-functionalities (R ) CH 3 , CH 2 CH 2 COOH, CH 2 CH 2 CH 2 SO 3 -, CH 2 CH 2 COO-Cholesteryl). The solvent effect was assessed by following the thermal decay of the photochemically ring-opened merocyanine to the spiropyran (MC H SP) via UV/vis spectroscopy at the λ max of the MC form. It was found that while modification of the N-moiety produced no perturbations in the solvatochromic behavior of these dyes, there was a marked effect on the solvatokinetic behavior. In nonpolar solvents, where the MCs possess predominantly quinoid character (unit central bond order), a constant thermal reversion rate was observed for the MCs with electron-rich N-ligands. This was attributed to electronic and steric interactions between the ligands and the phenoxide moiety. However, in polar solvents the increased zwitterionic character of the MCs (central bond order ∼2) leads to inhibition of the thermal reversion rate for the MCs in this study, independent of N-functionality. The MC H SP interconversion has also been examined by means of semiempirical calculations. These reveal the lowest energy pathway for conversion of the trans-MC to a cis-MC form via sequential bond rotation of the three central dihedral angles (R, β, and γ). The calculations support the observed solvatokinetic behavior, leading to the assignment of the trans/cis thermal isomerization as the rate-determining step in the overall process.
“…A promising class of organic materials for data processing are photochromic systems, that is, molecules that can be interconverted between two bistable forms by light. In the past photochromic systems based on cis – trans isomerization or photocyclization reactions have been studied4–7 and apart from fascinating results also severe problems that concern insufficient discrimination between read‐out and switching, low fatigue resistance, and/or weak contrast between the signals registered from the two states have been reported 8–14. Herein we present a photochromic system that consists of two perylene bisimide (PBI) units that are covalently linked to a dithienylcyclopentene (DCP; for details of the chemical synthesis see the Supporting Information).…”
It takes three: The key functionalities of an optical transistor, gating and amplification, are demonstrated exploiting the photophysical properties of a molecular triad (see picture). Two building blocks of the triad are highly efficient fluorophores, whereas the third building block is a photochromic molecule that can be reversibly interconverted between two bistable forms by light.
“…The phenomenon of photochromism of spiro-indolizines and spiro-pyrrolopyridazines was investigated by Durr et al [119][120][121][122][123][124][125][126] X-ray analysis of pyrrolopyridazines and their dihydro-and tetrahydro-derivatives was used by several research groups for structural determination and SAR analyses. 4,5,51,88,143,158,162 For further use in SAR correlations, as long ago as 1968 computational methods were used, on the basis of which the electron densities and ionization potentials were calculated.…”
Section: Physico-chemical and Biological Propertiesmentioning
Although a relatively simple system, pyrrolo[1,2-b]pyridazines have been subject to numerous studies and synthetic attempts. The present review represents an update to the 1976 review of Kuhla and Lombardino.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
