Substituent‐Dependent Reactivity in the Photodimerization of N‐Substituted Dibenz[b,f]azepines

Abstract

The photoprocesses of a series of N-substituted dibenz[b,f]azepines (iminostilbenes) were studied by absorption and emission spectroscopy, by laser flash photolysis, and by preparative irradiation with NMR analysis. In solutions, 2pi+2pi photodimers of N-cyano and N-acyl dibenzazepines are formed via the triplet state upon acetone- or benzophenone-sensitized energy transfer. T-T absorption spectra were measured and absorption coefficients were determined. The triplet energy transfer is equally efficient for N-alkyl dibenzazepines, which do not dimerize. Excited states of npi* character in the latter cases are discussed to rationalize the different reactivities. In spite of negligible intersystem crossing of 21 dibenzazepine derivatives, photodimers of N-acyl and N-cyano dibenzazepines are formed upon direct excitation in concentrated solutions (0.01-0.1 mol dm(-3)) as well as in the solid state. A selective anti-configuration of the photodimers was found throughout.

Photodimerization of coumarin revisited: Effects of solvent polarity on the triplet reactivity and product pattern

“…For photolysis with UV-vis detection an excimer laser (l exc ¼ 308 nm, rise time <20 ns), a transient digitizer (Tektronix 7912AD) and an Archimedes 440 computer for data handling were used as in previous work. 27,28 For few additional experiments an excimer laser (l exc ¼ 248 nm) or the third harmonic from a Nd-laser (l exc ¼ 354 nm, rise time 10 ns) were used. It was appropriate to apply l exc ¼ 354 nm to measure k 3 since the required coumarin concentration (up to 10 mM) is too high for excitation at 308 nm.…”

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…Product 98 for example was formed as a single diastereoisomer in a yield of >90% from substrate 97 (Scheme 32). 215 3.2.3. Isoquinolones and Isocoumarins.…”

Photophysics and Photochemistry of Imipramine, Desimipramine, and Clomipramine in Several Solvents: A Fluorescence, 266 nm Laser Flash, and Theoretical Study

“…This is in agreement with the observations made for this and other derivatives containing different substituents at the 5 and 10 positions. 44 The compounds with the lowest fluorescence quantum yield are the 5-acyl ISB derivatives. 44,45 If the ring nitrogen is replaced by a CHR-group, as in the case of DBCH and PTL, then the system turns out to be strongly fluorescent and the quantum yield can be as high as 0.86.…”

“…44 The compounds with the lowest fluorescence quantum yield are the 5-acyl ISB derivatives. 44,45 If the ring nitrogen is replaced by a CHR-group, as in the case of DBCH and PTL, then the system turns out to be strongly fluorescent and the quantum yield can be as high as 0.86. 20,39,46 The analog to DBCH, cis-stilbene, has no fluorescence because radiationless deactivation is induced by the fast free rotation cis/trans-isomerization.…”