Jörg Daub

Functionalized photochromics for molecular switching: the multistabilities of a dihydroazulene–anthraquinone system

Addressability and multimode activity of the dihydroazulene–anthraquinone conjugate 1 are investigated by photochemical and electrochemical techniques, establishing pH-dependent redox behaviour and dihydroazulene–vinylheptafulvene photochromism (1⇆2), enabling an electric current to be modulated by light-pulse-irradiation.

Oxidation state dependent light sensitivity of a ferrocene/dihydroazulene conjugate

Abstract The synthesis of 1, 8a-dihydro- 2-ferrocenyl-1,1-azulenedicarbonitrile ( 1a ) is described. Photochemical and electrochemical properties are investigated.

Photoreaction of dihydroazulenes into vinylheptafulvenes: photochromism of nitrophenyl-substituted derivatives☆

Abstract The photophysical and photochemical properties of five nitro-substituted dihydroazulene (DHA) derivatives, 1,8a-dihydro-2-(R-phenyl)-1,1-azulenedicarbonitrile, where R is 2-NO 2 , 3-NO 2 , 4-NO 2 , 2,4-(NO 2 ) 2 and 3,5-(NO 2 ) 2 (2-, 3-, 4-, 2,4- and 3,5-D respectively) were studied in solvents of different polarity at various temperatures. Irradiation of the DHAs in fluid solution leads to the corresponding vinylheptafulvenes (VHFs) which show neither emission nor photoreactivity. At room temperature, the quantum yield of the DHA → VHF photoreaction depends on the substitution and solvent; Φ D→V is substantial for 4-D (approximately 0.5) and very small (0.02–0.005) for 2- and 2,4-D, while for 3- and 3,5-D Φ D→V decreases with increasing solvent polarity. Fluorescence from the excited singlet state of 4-, 3- and 3,5-D is observed at low temperatures; the quantum yield is largest for 4-D ( Φ f ⩾ 0.5 at −196°C) and much smaller (0.002 or less) for 2- and 2,4-D. At room temperature, Φ f is very low throughout. The absorption spectrum of the triplet state is observed at room temperature for those cases, e.g. 2-and 2,4-D, for which Φ D→V is small, and enhanced triplet-triplet absorption is found in all cases using sensitizers, e.g. xanthone in acetonitrile. The DHA triplet energy was estimated from energy transfer measurements to be about 220 kJ mol −1 . The triplet state is not involved in the photochromism of the nitro-substituted DHAs. The effects of nitro groups at different positions in the phenyl ring on the photophysical and photochemical behaviour are discussed.

Novel Multichromophoric Dyes for Chemical, and Physical Switching

Abstract Functionalized photochromic compounds and their applications in chemical and physical switching processes are under investigation. In this report exclusive consideration is given to the dihydroazulene @HA)/vinylheptafulvene (VHF) system ½. A short description of the photochromism of ½. is presented. Three topics of potential switching behaviour released by the photochromism of ½. are pointed out: (i) change of the pka and of proton transfer properties in anilinium derivatives, (ii) change of the redox potential in compounds with electron transfer active subunits, (iii) increase of second‐order nonlinear optical properties by irradiation of 1.

Tetraoxa-[26]annulenochinon☆

Abstract The title compound and its electrochemically prepared dianion may be considered as the largest known macrocyclic quinone/hydroquinone-system.

Counterion and solvation effects on the conformations of the radical anions of 2,5-dicyanovinyl substituted furan and thiophene. An EPR and ENDOR study

The radical anions of two tetranitrile compounds, i.e., 2,2′-(furan-2,5-diyldimethylidene)-bispropanedinitrile (1) and 2,2′-(thiophene-2,5-diyldimethylidene)bispropanedinitrile (2), have been investigated in a 1,2-dimethoxyethane/N,N,N′,N′,N″,N″-hexamethylphosphoric triamide mixture, 1,2-dimethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran as the solvents and with Li+, Na+, K+, Cs+ as the counterions and in N,N-dimethylformamide with Zn2+ as counterion. A remarkable dependence of the molecular symmetry upon ion-pair formation is found for both molecules. The symmetry of both radical anions increases to C2ν under conditions favouring contact ion-pair formation.

An electron-transfer induced reaction path controlled by ion-pair formation: an ESR/ENDOR study of furan carbaldehydes and their reactivity

When furan 2,5-dicarbaldehyde 1 is single-electron reduced to its radical anion 1˙– its readiness to couple to give dimer 2 depends upon the nature of the ion pair 1˙–/M+(M = Li, Na, K, Cs).

[C6H6]n hydrocarbons. Tetracyclic C12H12 compounds from C18H18 precursors

Photochemical rearrangement of the polycyclic homotropylidene carbonate (4) yieds the heptacyclic carbonates (5), (6), and (8), from which the tetracyclo[4,4,2,02,5,07,10]dodecatrienes (1)–-(3) are synthesized.