Femtosecond dynamics of the photochromic reaction of a thiophene
oligomer with a diarylethene structure
in solution was analyzed by transient absorption spectroscopy. It
was found that the intermediate species
with an absorption maximum at ∼515 nm was formed within 100 fs and
that the closed-ring form of the
thiophene oligomer was formed mainly from the intermediate with a time
constant of ∼1.1 ps.
Thiophene oligomers having a dithienylethene structure show large shifts in oxidation potential to the cathodic region in excess of 0.87-1.27 V by photocyciization.
Two distinct fluorescence modes of a thioindigo compound substituted with two pyrene groups on the 7 and 7' positions were controlled by geometrical photoisomerization of the thioindigo skeleton.
Six bis(4-cyano-1-pyridinio) derivatives have been synthesized and deposited onto electrodes by cathodic electropolymerization (ERed = −0.64 — −0.74 V vs. SCE) under basic conditions. The deposited films were constructed of polyviologens that showed characteristic electrochromisms with colorless or slightly yellow to blue- or red-violet. The derivative was reduced to 4-cyano-1,4-dihydro-4-pyridyl radicals, which were coupled successively to form a polyviologen film on the electrode with an elimination of cyanide ions. Characteristically, the polyviologen films deposited by this electropolymerization were insoluble in water and common organic solvents with a spontaneous cross-linking. Especially, a polyanion as a supporting electrolyte forced the polyviologen to form a polyelectrolyte complex in situ. The current efficiency of surface coverage with the polyanion electrolyte (23% in the typical case) was about four-times larger than those with monomeric anions.
Several molecules having multiple regions independently responsive to stimulations have been investigated. A 2-(4-methoxyphenylazo)anthraquinone (1 ) having both an electrochromic quinone group and a photochromic azo group has been synthesized and its electrochromic and photochromic properties investigated. It shows interconversion of four distinct states caused by multiplication of two electrochromic redox states, quinone and hydroquinone, and two photochromic geometrical isomers, anti and syn forms. Moreover the syn-anti thermal isomerization rate of the azo region of the molecule is dependent on the state of the electrochromic quinone region. The rate for the quinone form is more than 30 times faster than that of the hydroquinone form. Additionally three other azoquinone compounds
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