97135-75-6Relevant academic research and scientific papers
The Role of Triplet States in the Trans - Cis Photoisomerization of Quaternary Salts of 4-Nitro-4'-azastilbene and Their Quinolinium Analogues. 6
Goernen, Helmut,Schulte-Frohlinde, Dietrich
, p. 4105 - 4112 (1985)
The quantum yields of fluorescence (φf) and of trans -> cis photoisomerization (φt->c) were measured for quaternary salts of 4-nitro-4'-azastilbene derivatives (At+X-; At+ = trans-1-alkyl-4-pyridinium and quinolinium; X(1-) = I(1-), ClO4(1-), and CH3SO4(1-)) as a function of solvent polarity, temperature, and concentration of quenchers.Transients (lifetime ca. 200 ns at 25 deg C, λmax ca. 450 nm) observed by laser flash photolysis were identified as the trans triplet configuration of either the cation (3*At+) or the ion pair (3*At+...X-) in highly and less polar solvents, respectively.In polar solvents at room temperature 3*At+ is quenched by oxygen, azulene, ferrocene, and I(1-) at rates close to the diffusion-controlled limit.The quenching measurements under pulsed and steady-state conditions suggest that 3*At+ is an intermediate in the trans -> cis photoisomerization route.In contrast to the pyridinium salts, φt->c does not follow for the quinolinium salts linear Stern-Volmer dependences on , , or .It is concluded that for the pyridinium salts trans -> cis photoisomerization occurs only via the triplet mechanism, whereas a second route, bypassing the lowest triplet state, contributes to a certain extent (ca. 40percent) for the quinolinium salts (mixed singlet-triplet mechanism).
