How many degrees of unsaturation are lost or gained in the base-induced transformation from mito-ph to its photoactive ring-opened form?

Unsaturation (IHD) 2 hydrogen Needed

IHD = [(2n+2) -H]/2
(H: X=1, N=-1, O= zero)

Unsaturation:
Double bonds = 1
Rings = 1
Triple Bonds = 2

The degrees of unsaturation in a molecule are additive — a molecule with one double bond has one degree of unsaturation, a molecule with two double bonds has two degrees of unsaturation, and so forth.

c (diamond),

sio2 (quartz)