Dispersion interactions, electronic absorption spectra of anthracenes in polar glassy media at 77–300 K, and the change in polarizability upon excitation

Abstract

The effect of dispersion interactions on the electronic spectra of organic compounds is analyzed within second-order perturbation theory. A formula is obtained which makes is possible to determine the change in the polarizability of the molecules upon excitation, ∆α eg , using data on the effect of the bulk polarizability P n of the solvent on the position of the electronic spectrum. It is shown that when the solutions are cooled, the long-wavelength shift of the absorption spectra for the studied anthracenes in alcohols is mainly due to dispersion interactions and is caused by an increase in P n . The possibility of using the new formula for ∆α eg is demonstrated for anthracenes as an example. It is found that for anthracene, 1-chloroanthracene, 9,10-dichloroanthracene, 9,10-dibromoanthracene, 9,10-diiodoanthracene ∆α eg is 16.5, 16.9, 17.2, 18.6, and 20.2 Å 3 respectively.

Effects of electronegative substitution on the optical and electronic properties of acenes and diazaacenes

“…The expected acene-type vibronic fine structure is observed for all of the compounds and, although the extinction coefficient decreases on addition of the electronegative substituents, the effect is not dramatic, suggesting that these materials could be useful absorbers. Electronegative substitution on π systems can lead to either blue-or redshifted or almost unchanged absorption spectra; chlorination, for example, induces bathochromic shifts in 9,10-dichloroanthracene 17 and in some chlorinated nitro-aminodiazobenzene derivatives of disperse red 18 . Such electronegativity effects occur if either the HOMO or the LUMO is particularly stabilized or not; they are especially pronounced in molecules with disjoint orbital structures, where HOMO and LUMO are localized on different parts of the molecule.…”

“…Chlorination lowers both HOMO and LUMO, but with the former effect insufficient to preclude hole injection, whereas the latter effect facilitates electron injection; however, the optical gap does not change to any appreciable extent 15 . The tetrachloro substitution only led to a slight shift in the absorption maximum going from 643 nm for 5 16 to 654 nm for 6 in solution, suggesting that chlorine substitution had comparable impact on both the ground and first excited states [17][18][19] . Lowering the absorption energies can be useful in the context of organic solar cells when looking for acene derivatives showing absorption into the near-infrared, as observed in Anthony's hexacenes and heptacenes 20,21 .…”

Evaluating the Solvent Stark Effect from Temperature‐Dependent Solvatochromic Shifts of Anthracene

“…This allows one to exclude the solute radius a (not well‐defined in the continuum dielectric theory) and to express B Stark through the well‐measured quantity B n that provides an improved estimate for the Stark shift. With =16.5 Å 3 , and taking I =7.4 eV for anthracene, I′ =10.4 eV for n‐pentane, one calculates C =69740 cm −1 . And with our experimental B n =3150 cm −1 (see Figure ) this gives at T= K …”

“…The anthracene polarizabilities have already been calculated . Pavlovich considered the temperature‐dependent shifts of absorption in frozen glassy alcohols where the Stark effect and the dispersive contribution were added up.…”

“…The anthracene polarizabilities have already been calculated . Pavlovich considered the temperature‐dependent shifts of absorption in frozen glassy alcohols where the Stark effect and the dispersive contribution were added up. Mathies and Albrecht performed electric field perturbation spectroscopy in a frozen medium, and Bendkowsky et al .…”