ThreeC2-symmetric(10R,11R)-diethylsubstituteddibenzosuberane(DBS)-basedheliceneswithvaryingstericandconjugationdemandsoftheirbottomfragmentsweresynthesized.Onlythehelicene-7a[withthebottompartderivedfromtetralonewasfoundphoto-switchableinreasonabletimescale.Photoisomerizationofthediastereomericallypure(10R,11R,P)-helicene(7a)at280nmledtovirtuallyexclusiveformationoftheoppositeMform-diastereomer7a′(7a′/7a=99.6/0.4).Thepreferentialreturnof7a′to7acanbeeffecteduponirradiationat254nm(7a′/7a=3G/67)orthermallyat1307a′/7a=0/100).Thephoto-inducedswitchingprocessamountstoa133%differenceind.e.(from99.2%to-34%).TheconcomitantchangeofhelicenechiralitybetweenthesetwodiastereomericphotostationarystatesaugurswellfortheirpotentialapplicationasanopticalswitchinLCmaterials.Toourknowledge,oursystemservesasthebestchirochromicopticalswitchascomparedtotheexamplespossessingsimilarphotochromicproperties.
