A DUAL-MODE MOLECULAR SWITCHING DEVICE - BISPHENOLIC DIARYLETHENES WITH INTEGRATED PHOTOCHROMIC AND ELECTROCHROMIC PROPERTIES

The bisphenolic dithienylethene molecules 1a and 1b were synthesized i n overall yields of 45% from 4-bromoanisole and 44% from 2,6-di-tert-b utyl-4-iodophenol, respectively. The corresponding extended quinones 3 a and 3b were also prepared. Photochemical studies showed that compoun ds 1 are photochromic; the open forms 1 could be converted with UV lig ht of 312 nm to the closed coloured forms 2 with photostationary state s lying at essentially complete conversion (> 98 %). The 1a-2a system was found to exhibit good resistance to photofatigue and thermal stabi lity for both photoisomers. Cyclic voltammetry studies involving the 2 /3 couples showed that whereas 2b undergoes irreversible oxidation at + 0.85 V (vs. SCE in THF), the hydroquinone 2a is reversibly oxidized at an E(1/2) of + 0.72 V (in MeCN, quasi-reversibly in THF at + 0.81 V ); this reflects the differences in deprotonation behaviour of the gen erated QH(2)(2+) species. The large difference in oxidation potential between 1a and 2a allows the photochemical switching of redox properti es. In a complementary fashion, redox switching of the photochromic pr operties within the 2a-3a pair is possible since 3a is stable to visib le light. Owing to this unique behaviour, the triad consisting of 1-3a represents a novel molecular device with mutually regulating photo- a nd electrochromic behaviour. In addition, the ability to interconvert between the three stable states makes the system well-suited as the ba sis for an optical memory system with multiple storage and nondestruct ive readout capacity through a write-lock-read-unlock-erase cycle.