diethyl dihydro pyrene-cyclophanediene

3. *Dihydropyrene is a promising class of photoswitches and classified as negative T-type photochromoes.
(T-type behaviour is exhibited if light is able to drive the change in just one direction)
*The closed form, (dihydropyrene, (DHP)) is colored and thermodynamically more stable as compared to
colorless open cyclophanediene (CPD).
*Thermal closing of CPD-DHP, in neutral singlet state proceeds through conrotatory 6π electrocyclization,
which is forbidden according to Wood-ward Hoffman rules of orbital symmetry

4. The thermal reaction is Woodward-Hoffmann forbidden
Conrotatory closure necessary for steric reasons
Eact ~ 19-26 kcal/mole for a variety of systems
The best DHP based photoswitch
Visible
UV
Eact = 25 kcal/mol
Photo opening is fast
t1/2 (days) 7.3

5. CHO
CHO CHO
Br
Br
OO
CHO
O
Thermal closing rates at 20oC
FAST
MEDIUM
SLOW
t1/2 (min) 42 51 90 200
t1/2 (h) 30 42 45 49 54
t1/2 (days) 7.3

6. E
Reaction Coordinate
CPD DHP
TS*
CF3
CN
CN
CF3
Me
Me

7. Br BrCN
S SCN
CN
2
NC
CN
SMe
MeS
CNNC
NC
CN
Na2S.9H2O,
Benzene,
EtOH,H2O.
1.Borch Reagent
CH2Cl2
2. KOtBu, THF
1.Borch Reagent#,
CH2Cl2
2. KOtBu, THF
UV
Visible*
* = Photo stationary state , DHP : CPD 40 : 60
35% Overall
#Borch Reagent = (MeO)2CH BF4