Schmierer, T.; Ryseck, G.; Villnow, T.; Regner, Nadja; Gilch, P.
Kasha or state selective behavior in the photochemistry of ortho-nitrobenzaldehyde?
In: Photochemical & Photobiological Sciences, Vol. 11, Nr. 8: S. 1313-1321
The photochemistry of ortho-nitrobenzaldehyde dissolved in tetrahydrofuran was studied by means of femtosecond UV/Vis and IR spectroscopy. Comparison was made of the spectral and temporal signatures for similar to 400 nm and similar to 260 nm excitation. The 400 nm excitation promotes NBA to its lowest excited singlet state of n pi* character whereas for 260 nm an upper excited state of pi pi* character is addressed. On the picosecond time scale, the molecule undergoes hydrogen transfer, yielding a ketene intermediate, internal conversion recovering the starting material, and intersystem crossing. Time constants and yields of these processes are virtually not affected by the excitation wavelength. For 400 nm excitation a similar to 100 fs decay component seen in the 260 nm experiment is absent, indicating that this component is due to a pi pi* -> n pi* internal conversion. In contrast to its formation, the decay of the ketene intermediate is influenced by the excitation wavelength. This can be attributed to different amounts of vibrational excitation.