Anthracene vibronic transitions

Figure 2.6 Absorption spectrum of a solution of anthracene in benzene, and the vibronic transitions responsible for the vibrational line structure...

Figure 6 Emission (solid line) and absorption (dashed line) spectra of anthracene in solution. The assignments of the vibronic transitions are shown in the bottom portion of the figure. Reproduced with permission from Turro NJ (1978) Modem Molecular Photochemistry, p 94. Menlo Park Benjamin/Cummings.

Unfortunately, the experimental information for anthracene is not as rich as for naphthalene. Transitions to the lowest 7r-excited state occur at 1.1 eV and are dipole forbidden. In addition, PES [161,162] predicts transitions at 1.76,2.73, and 2.81 eV. The EA spectrum [166] of anthracene recorded in argon matrices agrees with the absorption maxima in organic glasses [140], and the vibronic fine structure is in accord with the Raman spectrum of polycrystalline anthracene [167] at room temperature. The CASSCF/CASPT2 calculations presented by... 

Fig. 6.6 The absorption spectrum of an anthracene crystal and of anthracene in an ethanolic solution. The crystal is oriented with its fl - plane perpendicular to the optical beam direction. Transitions from the Sq into the vibronic levels of the Si and S3 states are...

In triplet transitions, the resonance interaction and thus the Davydov splitting can, as mentioned, no longer be understood in terms of a dipole interaction, but rather as an exchange betv een orbitals which overlap. Measured values are available only for Ti states. Figure 6.10 shows as an example, similar to Fig. 6.1, the two 0,0 components of the excitation spectrum Ti So, of the triplet exciton Ti in an anthracene crystal here, however, the spectrum was taken at 1.8 K. 0,0 transition means that the excitation affects only excitons and that no additional phonons or vibrons are excited. In anthracene, the Davydov splitting of the Ti excitonic state is 21.5 cm" (cf Fig. 6.10). In naphthalene, it is 9.8 cm [34]. 

Deeper traps can in some cases be emptied by irradiation with light. Figure 8.42 shows as an example the excitation spectrum of the photocurrent in an anthracene crystal which was doped with 10 tetracene molecules and whose hole traps were previously filled at a lower temperature, so that the anthracene crystal contained tetracene radical-cations before the excitation. The excitation spectrum shows the 0,0 transition and the vibronic series of the energetically lowest doublet-doublet transition Di Dq in the tetracene radical-cation. The combined evaluation of the thermally and the optically-stimulated currents yielded in this special case a value = 0.42 eV for the depth of the hole traps represented by tetracene in an... 

In most organic crystals, however, the first absorption regions are less Intense and show weak coupling characteristics. In the anthracene crystal, for instance, the vibronic envelope of that transition is nearly the same as in solution. However, the vibronic bands are individually split, each into two components, with separations from 100-200 cm . With some reservations we may say that the vibronic interaction energies between nearest neighbours in the lattice are of the same order of magnitude. 

The anthracene sym-trinitrobenzene complex was studied as a dilute solute in glasses and host crystals. The CT absorption and fluorescence spectra in both types of media were found to be essentially identical (e.g., vibronic bandwidths 1000 cm ). Furthermore, the CT fluorescence origin band in the glass was invariant to the location of the laser excitation frequency within the origin band of the CT absorption spectrum. The results of ref. 21 lead to Ft 300 cm" for this 100% CT transition. It is, therefore, germane to... 

PPV-type polymers have been widely investigated for their third-order NLO properties. Polymers 120 and 121 are PPV-type polymers with anthracene substitution in the side-chain. The optical properties of these polymers can be considered as a composition of the interlinked stmcture of diphenylanthracene and derivatized PPV. Phenylanthracene-containing polymers exhibit four vibronic bands in the region of 325-410 nm overlapped with weaker broader absorption at longer wavelength region that arises from the electronic transitions from the main chain. The absorption maxima of the two polymers do not show much variation with maxima at 335, 355, 373, and 394 nm. These values are red-shifted compared... 

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