Photochemical and photophysical studies of bicyclo[4.3.0]non-1(6)-en-2-one

• Published in: Journal of the American Chemical Society Vol. 114; no. 18; pp. 7029 - 7034
• Main Authors: Schuster, David I, Woning, Jan, Kaprinidis, Nikolas A, Pan, Yanping, Cai, Bing, Barra, M, Rhodes, Christopher A
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 01.08.1992; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; General and physical chemistry; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Physical Sciences; Science & Technology; KETONES; STATES; RESOLVED PHOTOACOUSTIC CALORIMETRY; SPECTROSCOPY; TRIPLET; ENONES; ABSORPTION; ENERGIES; Stern Volmer diagram; Reaction intermediate; Triplet state; Near ultraviolet radiation; Laser beam; Organic free radical; Bicyclic compound; Flash photolysis; Quantum yield; Enone
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00044a012

The properties of the lowest excited triplet state of bicyclo[4.3.0]non-1(6)-en-2-one (BNEN) have been investigated by nanosecond transient absorption spectroscopy, photoacoustic calorimetry, measurements of O-1(2) quantum yields, and photochemical studies in solution. Both the lifetime (1.4-mu-s) and the energy (74-76 kcal mol-1) of the BNEN triplet reflect its exceptional conformational rigidity, which prohibits relaxation along the 3(pi,pi*) potential energy surface by twisting around the C=C bond. Fumaro- and maleonitrile quench the BNEN triplet at a diffusion-controlled rate by triplet energy transfer. This process leads to cis-trans isomerization of the alkenes. The BNEN triplet displays extensive self-quenching with k(sq) 2.6 X 10(7) M-1 s-1. This process involves intermolecular H-abstraction, but formation of dimeric triplet 1,4-biradicals cannot be excluded. The product of the former is a radical (3) with a lifetime of 4.1-mu-s. Its transient absorption spectrum (lambda(max) 299 nm) is hypsochromically shifted with respect to that of the BNEN triplet (lambda(max) 311 nm). The solvent effects on the photophysical properties suggest that the T1 state of BNEN is a (pi,pi*) state in acetonitrile and an (n,pi*) state in benzene. The BNEN triplet undergoes neither [2 + 2] cycloaddition reactions with itself, cyclopentene, fumaronitrile, or maleonitrile nor the lumiketone rearrangement, but readily abstracts H-atoms from itself, cyclopentene, and 2-propanol.