bicycle-pedal (BP) mechanism
Volume-conserving mechanism proposed for the photoisomerization
of conjugated double bonds. Two alternating double bonds rotate concertedly with
only the two
units turning in and out of the plane of the molecule.
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 308