Synthesis And Photochromism Of Carbazole-based Dithienylmaleimide Derivatives

To improve the stabilities of dithienylmaleic anhydride (DTMA) and dithienylmaleimide(DTMI) derivatives, N-substituted carbazole moiety is invited to DTMA to give N-substitutedcarbazole-dithienylmaleimide derivatives, and21products were synthesized including ortho(1-11) and para series (12-21). All of the compounds are confirmed by1H NMR,13C NMR,MS and Elemental Analysis.The photochromic behaviors of the ortho series were studied via UV-Vis spectra. Resultshowed no photochromism in compound1, which features an N-site unoccupied carbazolemoiety. As for2-11a phenomenon is observed that steric and electric effects play a decisiverole in the photochromic change strength.In additional to the ortho series, photochromism of para series was studied by analyzing thecorresponding UV-Vis absorption spectra likewise. As expected, compounds in para series,featured by no direct steric hindrance between N-substituent on carbazole moiety and theDTMI moiety, exhibited no perceivable photochromic behaviors, no matter what kinds of thesubstituents were introduced.The phenomenon mentioned above was explained by refering the Taft’ steric substituentconstant Es(R), Esc(R) and v(R) and Hammett’s constant σ. Result showed good Pearsonrelation between Esc(R) and v(R) and the relative strength coefficient R of1-8, whichindicates encouragement of bulky hindrance to the photochromic change strength. As for6-10,good Pearson relation between σ and R indicates that electric withdrawal ability boosts thecoloration change strength as well.At last, Photostability and fatigue-resistance spectra of compounds2-11and DTMA wererecorded and further studied. Several results were obtained. First, excellent photostabilitywere observed in compounds2-10, especially9and10of which97%of the maximumabsorption at377nm remain after its exposure to254nm ultraviolet irradiation for20min.Secondly, compound11with the largest electric withdrawal ability and bulky hindrance,shares a lot common with DTMA including florescence in open-ring form, photo-unstability and similar characteristic absorption. Third, the tested samples displayed consistantfatigue-resistance and photostability characteristics. Lastly, a critical point was observed inthe manifestation of coloration strength by hindrance and electric effect, which example11explains well.In sum, compounds9and10, which exhibited excellent photostability and photochromicchange strength, were ranked as the most promising compounds in our system, in terms ofboth aspects.