10a-(4-Biphenyl)-10b-methyl-10a,10b-dihydropyrene: a conformational study and ring current effect

A dithiacyclophane was employed as a precursor to the title compound. A conformational study of the dithiacyclophane revealed a unique phenomenon in its terphenyl unit: one ring is rigidly held, the other terminal ring undergoes free rotation and the central ring exhibits restricted mobility. The aromatic protons of the biphenyl unit are all shielded by the dihydropyrene unit and well resolved in the ¹H NMR spectrum, consistent with a ring current effect extended to eight conjugated carbon atoms away from the molecular plane of dihydropyrene.     

Characterization of the photochromism of dihydropyrenes with photophysical techniques

Dihydropyrenes are negative photochromes and their photophysical characterization, achieved in the past decade, is reviewed. Special emphasis is given to the theoretical background and to the experimental details which are relevant for the characterization of bi-stable systems, such as photochromic ones. In contrast to most photochromic compounds, dihydropyrenes have long lifetimes for their photoreactive excited states making it possible to tune their reactivity with the introduction of substituents. This knowledge is applicable for the design of more efficient photochromic molecules and for multichromophoric systems.     

Synthesis and photochromic properties of quinoxalino[e]-annelated dimethyldihydropyrene with planar chirality

9,10-Diacetyl-2,7-di-tert-butyl-trans-10b,10c-dimethyl-10b,10c-dihydropyrene annelated with a quinoxaline unit (q-DM-DHP, 3) was prepared from 5,13-di-tert-butyl-8,16-dimethyl[2.2]metacyclophane-1,2,9,10-tetraoxide (2) and o-phenylenediamine in two steps. The photochromic isomers of q-DM-DHP 3, closed form 3a and open form 3b, were separated by reverse-phase HPLC, and their isolated UV–visible spectra were estimated. The chiral HPLC analyses of q-DM-DHP 3 indicated their planar chirality, and their CD spectra were measured. The photochromic properties and thermodynamic properties of 3 were also discussed based on their UV–visible, ¹H NMR, CD, and fluorescence spectra.