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On the Photochromism of Spiro[cyclohexadiene‐dihydroacridines]
Author(s) -
Häupl T.,
Zimmermann T.,
Hermann R.,
Brede O.
Publication year - 2000
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2000)0710294otposc2.0.co2
Subject(s) - photochromism , photoisomerization , merocyanine , photochemistry , chemistry , picosecond , ultrafast laser spectroscopy , excited state , irradiation , absorption spectroscopy , singlet state , absorption (acoustics) , photodissociation , isomerization , spectroscopy , materials science , laser , organic chemistry , catalysis , optics , physics , quantum mechanics , nuclear physics , composite material
The recently synthesized spiro[cyclohexadiene‐dihydroacridines] consisting of perpendicularly arranged aroylcyclohexadiene and N ‐methyl‐dihydroacridine moieties were found to have photochromic properties. The reversible photoisomerization from the spiro compound toward a colored merocyanine caused by C–C bond cleavage in the cyclohexadiene was studied by stationary and time‐resolved measurements of their optical spectra. The course of the absorption under UV and visible irradiation, respectively, and HPLC analysis of the photoproducts result in the determination of excitation energy‐dependent quantum yields for the merocyanine formation and, in reverse, the ring closure, as well as degradation. Whereas the thermal back reaction completely recovers the spiro compound ( k ∼ 6.8 × 10 −4 s −1 , T = 22°C), degradation of the merocyanine under irradiation at 480 nm has a probability of about 6%. Picosecond‐resolved measurements of the fluorescence and the transient absorption show that photoisomerization occurs via the first excited singlet state within 100 ps depending on the activation barrier.