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

The bisphenolic dithienylethene molecules 1a and 1b were synthesized in overall yields of 45% from 4-bromoanisole and 44% from 2,6-di-tert-butyl-4-iodophenol, respectively. The corresponding extended quinones 3a and 3b were also prepared. Photochemical studies showed that compounds 1 are photochromic; the open forms 1 could be converted with UV light of 312 nm to the closed coloured forms 2 with photostationary states lying at essentially complete conversion (> 98 %). The 1a-2a system was found to exhibit good resistance to photofatigue and thermal stability 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 generated QH(2)(2+) species. The large difference in oxidation potential between 1a and 2a allows the photochemical switching of redox properties. In a complementary fashion, redox switching of the photochromic properties within the 2a-3a pair is possible since 3a is stable to visible light. Owing to this unique behaviour, the triad consisting of 1-3a represents a novel molecular device with mutually regulating photo- and electrochromic behaviour. In addition, the ability to interconvert between the three stable states makes the system well-suited as the basis for an optical memory system with multiple storage and nondestructive readout capacity through a write-lock-read-unlock-erase cycle.