Two new thermally irreversible photochromic
(R)-binaphthol-condensed indolylfulgides (with a
1-(1,2-dimethyl-3-indolyl)-2-methylpropylidene group and with a
1-(1,2-dimethyl-3-indolyl)butylidene group, 6 and
7,
respectively) were synthesized. Because of rapid thermal
equilibration between the conformational isomers of
7E
at room temperature, photocyclization of a substantial portion of
7E occurred through (P)-7Eα to give
(9aS)-7C
selectively. On the other hand, as thermal equilibration requires
a long time for 6E at room temperature, its
photochromic interconversion occurs only between
(P)-6Eα and (9aS)-6C, and
the photocyclization-inert 6E remained
unchanged. The thermal stability and fatigue resistivity toward
the iterative photochromic interconversion of 7
have
been proved to be excellent among the fulgide derivatives. The
photochromic reactions were accompanied by large
changes of specific rotation values. The X-ray crystallographic
analysis of a visible-light-sensitive colored form,
(9aS)-6C, was carried out.