J. Langelaar

Monomer and excimer phosphoresence of phenanthrene and naphthalene in solution

Abstract The phosphoresence spectra of phenanthrene and naphthalene have been measured in liquid ethanol solutions. Both spectra are superpositions of a structured and a broad structureless component. The structured component is ascribed to the triplet monomer, the structureless one to the triplet excimer phosphorescence emission. Decay constants for the two emissions have been measured as a function of the temperature.

Singlet excited monomer and excimer absorptions of pyrene

Abstract The absorption and polarization spectra from the first excited singlet state of pyrene and the absorption spectrum of the pyrene excimer are presented. These results were obtained by laser flash spectroscopy using a frequency doubled ruby laser pulse of 6 nanoseconds halfwidth. A qualitative preliminary assignment of the bands is given.

SCF Cl calculations and assignment of the S1 → Sn absorption spectra of 1,1′-binaphthyl in different molecular conformations

Abstract An SCF calculation followed by extensive configuration interaction between all singly-excited singlet states has been performed for 1,1′-binaphthyl as a function of the dihedral angle. With these results an assignment of the electronic absorption bands in rigid and in fluid solution is given.

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.

Triplet excimer emission from pyrene single crystals

Abstract Two new, but distinct delayed emissions are found from pyrene single crystals in the temperature region 77°–300°K, which are attributed to the emission of two types of triplet excimer.

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.

Polarization measurements on low-lying T-T absorptions with CW argon-ion laser photoselection

Abstract Extinction coefficients and the direction of polarization of the T-T absorption spectra of 1,2-benzcoronene, 1,1,2-benzyperylene and 1, 2, 3, 4-dibenzahtracene in the region of 5 000 to 26 000 cm−1 are reported. A comparison has been made between the results obtained with Hg arc and Ar laser excitation.

The influence of the molecular conformation upon spectroscopic properties of 1,1′-binaphthyl

Abstract The large difference in S 1 → S n absorption spectrum, fluorescence spectrum and fluorescence decay time of 1,1′-binaphthyl in fluid solution as compared to rigid solution can be related to a change of the molecular conformation of the fluorescent state.

On the lifetime of triplet monomers and excimers of aromatic hydrocarbons in solution

Abstract The triplet lifetime of aromatic hydrocarbons in liquid solution is relatively short compared with the lifetime in a rigid solution. Until now this difference has been explained by an impurity quenching mechanism. An alternative explanation is given, assuming quenching of a triplet molecule by a singlet ground state molecule of the same kind, resulting in the formation of a triplet excimer. A kinetic analysis of this mechanism is given. The results are discussed and compared with experiments.

The location, polarization and assignment of low lying excited triplet states in pyrene

Abstract It is concluded that the T n -T 1 absorption spectrum in the visible and near infrared is due to four electronic transitions, for which the 0-0 transitions are located at 10 300, ≈16 300, 19 200 and 24 200 cm −1 . They are assigned to the 3 B + 3g « 3 B + 2u . 3 A + 2u , 3 B − 3g « 3 B + 2u and 3 A − « 3 B + 2u transitions respectively. The 3 B + 3g state is shown to be situated only 400 ± 100 cm −1 above the first excited singlet state, which may explain the reported temperature dependent part of the intersystem crossing rate