C.J. Werkhoven

Intermediate strong coupling and vibrational redistribution effects in the S2 emission of pyrene

Abstract Upon excitation of pyrene in the third excited singlet state normal (τ = 75 nsec) and hot band (τ = 15 nsec) fluorescence of the second excited singlet has been observed. Both emissions exhibit intermediate strong coupling characteristics while the lifetime of the latter is also affected by a vibrational redistribution process.

Sequence congestion and temperature effects on the fluorescence of isolated pyrene molecules

Abstract The temperature dependences of (i) the relative yield of the S2 fluorescence and (ii) the fluorescence decay times measured in the S1 and S2 emission regions of pyrene vapour have been measured at very low pressures. The results demonstrate that the thermal equilibrium distribution of vibrational energy in the electronic ground state of the molecule is transferred to the excited electronic state by the excitation process. This phenomenon is ascribed to sequence congestion effects.

Excited singlet state polarization and absorption spectra of 1,2-benzcoronene, 1,12-benzperylene and 1,2:3,4-dibenzanthracene

Abstract The direction of polarization and the oscillator strengths of the S n ← S 1 absorption spectra of 1,2-benzcoronene, 1,12-benzperylene and 1,2:3,4-dibenzanthracene in the region 15 000–25 000 cm −1 are reported.

Relative S2 emission yield in the case of intermediate strong coupling

Abstract It is shown that in the case of intermediate strong coupling, the relative S 2 emission yield of isolated pyrene molecules is proportional to the ratio of the densities of states in the zero order S 2 and S 1 manifold.

Relative quantum yield of the S2 emission of naphthalene vapour

Abstract The spectrum and relative yield of the S 2 emission of naphthalene vapour obtained by pulse laser and cw excitation, is reported.

Effects of intramolecular vibrational redistribution in the S1 fluorescence of pyrene vapour

Abstract The fluorescence decay of pyrene vapour, excited into the S 1 -state with a frequency doubled ruby-laser pulse (28800 cm −1 ) has been studied under conditions where the excited molecules are collisionally unperturbed. The fluorescence decay curve can be described as a sum of two exponential components. The characteristics of the fluorescence decay are interpreted in terms of a vibrational redistribution process after excitation into a specific vibronic state. The rate constant for the vibrational redistribution is of the order of 10 7 sec −1 .

The effects of sequence congestion and weak coupling on the observed fluorescence lifetimes in different spectral regions in the case of intermediate strong coupling

Fluorescence decay times measured in the S1 and S2 emission regions are reported for a number of aromatic hydrocarbons in the vapour phase at low pressures. In contrast to the theory which applies to the intermediate strong coupling case, the decay times of the S2 emission are significantly shorter than the decay times of the normal S1 fluorescence. About half of this difference can be ascribed to sequence congestion effects. The effect of an additional weak coupling between S1 and S2 states cannot be excluded.

Energy dependence of the radiative and non-radiative decay constants of the S1 fluorescence of pyrene vapour

Abstract The radiative and non-radiative decay constants of the S 1 fluorescence of pyrene- h 10 , pyrene- d 10 and 3-methylpyrene in the vapour phase have been obtained as a function of the excitation energy from lifetime and quantum yield measurements. The calculated energy dependence of the radiative rate constant of pyrene is in good agreement with the experimental data.

Vibrational redistribution effects in the time resolved emission of isolated pyrene molecules

Abstract Arguments are given that the appearance of a short component in the fluorescence decay of pyrene after excitation in a vibronic origin of the S 0 → S 1 transition, has to be ascribed to a redistribution of vibrational energy of the inducing mode over the other vibrational modes in the molecule.

Incomplete vibrational relaxation of pyrene in its first excited singlet state in the vapour phase

Abstract The non-exponential fluorescence decay of pyrene is assigned to incomplete vibrational relaxation in the first excited singlet state. The increasing rate of this fluorescence decay with increasing vibrational energy is mainly attributed to an increase of the intersystem-crossing rate and to a smaller extent to a temperature dependence of the radiative rate constant.