Photochemistry of matrix-isolated cyclopentadienylidene revisited

Irradiation of diazocyclopentadiene (1) in a matrix at 10 K with the wavele ngth lambda = 366 nm leads-as already known-to rapid loss of nitrogen and t he formation of cycloprntadienylidene (T-2). Upon photoexcitation of cyclop entadienylidene (2) with light of the wavelength lambda = 313 nm the (s-E)- (E)-conformer of 2-penten-4-yn-1-ylidene (T-7a) can be detected, which is e ffectively converted into 3-ethynylcyclopropene (6) by using light with a w avelength of lambda = 436 nm. The structural elucidation of T-7a and 6 is b ased on the comparison of the experimental and calculated IR spectra. Irrad iation of cyclopentadienylidene (2), isolated together with the eliminated nitrogen in the same matrix cage, with light of wavelengths longer than 570 nm initiates a partial back-reaction to the starting material, diazocyclop entadiene (1) by recapturing the evolved nitrogen molecule. (C) 2000 Elsevi er Science B.V. All rights reserved.