Ring-closure and isomerization capabilities of spiropyran-derived merocyanine isomers.
We report the photochemistry of two ring-open isomers, namely TTC and TTT, of a bidirectional photoswitchable spiropyran, 6,8-dinitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6,8-dinitro BIPS). Both isomers are capable of ring closure after excitation with visible fs laser pulses, as disclosed by pump-wavelength-dependent transient absorption experiments in the visible spectral range. The main isomer TTC has its maximum absorption at 560 nm, whereas the minor isomer TTT is red-shifted (600 nm). The excited-state lifetimes differ strongly (τ ≈ 900 ps for TTT and τ ≈ 95 ps for TTC), nevertheless the quantum efficiencies for ring closure (40% for TTC and 35% for TTT) and isomerization (1-2% for TTC and 1-2% for TTT) are comparable. With regard to the bidirectional photoswitching capabilities, 6,8-dinitro BIPS is the first molecular switch based on a 6π-electrocyclic reaction where both ring-open isomers are capable of ring closure.
Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
Johannes
J
Buback
Patrick
P
Nuernberger
Martin
M
Kullmann
Florian
F
Langhojer
Ralf
R
Schmidt
Frank
F
Würthner
Tobias
T
Brixner
D001578:Benzopyrans / Q000138:chemical synthesis* / Q000737:chemistry*; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D009574:Nitro Compounds / Q000737:chemistry*; D010777:Photochemistry; D011789:Quantum Theory; D013237:Stereoisomerism
D001578:Benzopyrans; D007211:Indoles; D009574:Nitro Compounds; C548873:merocyanine; C088184:spiropyran