Optical and photophysical properties of anisole- and cyanobenzene-substituted perylene diimides

Bernard Pagoaga (1) , Olivier Mongin (2) , Monica Caselli (3) , Davide Vanossi (3) , Fabio Momicchioli (3) , Mireille Blanchard-Desce (4) , Gilles Lemercier (1) , Norbert Hoffmann (1) , Glauco Ponterini (3)

1 ICMR - Institut de Chimie Moléculaire de Reims - UMR 7312
2 ISCR - Institut des Sciences Chimiques de Rennes
3 UNIMORE - Università degli Studi di Modena e Reggio Emilia = University of Modena and Reggio Emilia
4 ISM - Institut des Sciences Moléculaires

One- and two-photon absorption cross-sections and spectra and the photophysical properties of eight perylenetetracarboxy-3,4:9,10-diimide (PDI) derivatives are reported and analyzed. The investigated compounds are characterized by direct binding of the phenyl rings of the substituents to the bay positions of the perylene core. They have been designed to test the effects of differences in the electronic nature - electron donating (anisole) or accepting (cyanobenzene) - and binding topology (cis or trans, meta or para disubstitution or tetrasubstitution) of the bay substituents on the above optical and photophysical observables. (TD)DFT and Hückel MO calculations have provided theoretical information on the ground-state geometries, the MOs and the electronic spectra of several model compounds. For tetrasubstituted and cis disubstituted derivatives, strong steric interactions in the bay area determined the preferred conformations, with perylene cores distorted near the substituted bay(s) and a 42-44° twisting of the substituent rings relative to the core, quite irrespective of the electronic nature of the substituents. On the other hand, in trans-disubstituted PDI steric hindrance in the bay areas was much weaker and similar in the cyanobenzene and the anisole derivatives. So, the large differences found in the conformational preferences were completely attributable to electronic effects. With electron-accepting cyanobenzene, the substituent rings were found normal to the central planar perylene core, thus enabling the assignment of the moderate spectroscopic effects to inductive interactions. The DFT analysis of the PDI trans-disubstituted with electron-donating anisoles gave quite strongly distorted perylene-core geometries and less twisted (59°) substituent rings. The corresponding increased substituent/core conjugative interactions resulted in new CT allowed electronic transitions and an extremely pronounced solvent-polarity dependence of the emission spectra and intensities. All anisole substituted PDI feature a very fast radiationless decay path in polar solvents, likely related to a relaxation to a charge-separated configuration in the lowest excited-state.

Mots clés: Perylene-diimides; Anisole substituents; Optical properties; Two-photon absorption

Domaines: Chimie

Bernard Pagoaga, Olivier Mongin, Monica Caselli, Davide Vanossi, Fabio Momicchioli, et al.. Optical and photophysical properties of anisole- and cyanobenzene-substituted perylene diimides. Physical Chemistry Chemical Physics, 2016, 18 (6), pp.4924--4941. ⟨10.1039/c5cp07758c⟩. ⟨hal-01269734⟩