Internal conversion rates for single vibronic levels of S2 in azulene

Abstract

Simultaneous measurements of absorption and fluorescence in a pulsed planar supersonic jet are used to determine fluorescence quantum yields of nine single vibronic levels (SVL’s) in the S2 electronic manifold of azulene. The quantum yield at the spectroscopic origin is 0.042±0.004, somewhat larger than that obtained in earlier room-temperature measurements in solution. Most SVL’s have quantum yields within experimental error of this value, except for two SVL’s characterized by large-amplitude motion at carbons 1 and 3, whose quantum yields are about 0.06. Our quantum yield data are combined with recent lifetime measurements by other workers to obtain fluorescence and internal conversion decay rates for each SVL. The radiative rates vary by a factor of 2, as expected for the S2↔S0 transition, whose absorption strength is strongly enhanced by vibronic coupling between S2 and S4. The internal conversion rates increase with excess vibrational energy in a way that parallels the extent of intramolecular vibrational redistribution (IVR), as determined by other workers using SVL emission and time-and-energy-resolved emission. Thus, the internal conversion rates in this electronic state appear to exhibit behavior typical of large aromatic molecules.

Rotationally resolved ultrahigh-resolution laser spectroscopy of the S2 A11←S A11 transition of azulene

“…This value is in good coincidence with the reported lifetime observed by real-time decay measurement with pulse-laser excitation. 19 We performed similar measurement and analysis for the 0 0 0 + 467 cm −1 band, which was assigned as 38 0 1 . 17 The 38 ͑b 2 ͒ mode is an in-plane skeletal deformation vibration.…”

“…17,18 Fluorescence lifetime and quantum yield have been measured for individual vibrational levels. 19,20 The lifetime of the zerovibrational level in the S 2 1 A 1 state is 3 ns, which is long enough to resolve each rotational line in the S 2 ← S 0 spectrum. The rotational constants in the S 0 1 A 1 state were precisely determined by microwave spectroscopy.…”

Non‐radiative deactivation of molecules. II. Theoretical study of the internal conversion rates in azulene

“…A number of studies nearly exclude the S, -So internal conversion channel from the vibrational ground level as a dominant radiationless deactivation [18,20,21]. On the other hand, a few hold the very opposite possible [ 191.…”

Time-dependent photoionization of azulene: Competition between ionization and relaxation in highly excited states

“…7 With increasing vibrational energy, the internal conversion rate is expected to increase slightly before tailing off at yet higher energy. 38,41 The overall trend of exponentially increasing IC k versus vibrational energy in S 2 has already been observed [7][8][9]41 for an excess vibrational energy greater than 0.24 eV. 2,8 In the framework of Fermi's Golden Rule, the internal conversion rate can be approximated as: …”

“…Figure 5 compares the rate e k measured at high excess energy in the present work with earlier gas-phase measurements at lower excess vibrational energy. [7][8][9]41 The value of This contour integral is done with a resolution of ∆E=10 meV, fixed by the convergence of the calculation, leading to a density of states: …”