title: Optical and photophysical properties of anisole- and cyanobenzene-substituted perylene diimides.
abstract: 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.
authors.affiliation: Université de Reims Champagne-Ardenne, ICMR UMR no. 7312, BP 1039, 51687 Reims Cedex 2, France. norbert.hoffmann@univ-reims.fr.
authors.forename: Bernard
authors.initials: B
authors.lastname: Pagoaga
authors.affiliation: Université Rennes 1, UMR CNRS 6510, Chimie et Photonique Moléculaires, Campus de Beaulieu, 35042 Rennes cedex, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Mongin
authors.affiliation: Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, via, Campi 183, 41125 Modena, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Caselli
authors.affiliation: Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, via, Campi 183, 41125 Modena, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Vanossi
authors.affiliation: Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, via, Campi 183, 41125 Modena, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Momicchioli
authors.affiliation: Université Bordeaux, ISM, Centre National de la Recherche Scientifique, UMR 5255, F-33400 Talence, France.
authors.forename: Mireille
authors.initials: M
authors.lastname: Blanchard-Desce
authors.affiliation: Université de Reims Champagne-Ardenne, ICMR UMR no. 7312, BP 1039, 51687 Reims Cedex 2, France. norbert.hoffmann@univ-reims.fr.
authors.forename: Gilles
authors.initials: G
authors.lastname: Lemercier
authors.affiliation: Université de Reims Champagne-Ardenne, ICMR UMR no. 7312, BP 1039, 51687 Reims Cedex 2, France. norbert.hoffmann@univ-reims.fr.
authors.forename: Norbert
authors.initials: N
authors.lastname: Hoffmann
authors.affiliation: Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia, via, Campi 183, 41125 Modena, Italy. glauco.ponterini@unimore.it.
authors.forename: Glauco
authors.initials: G
authors.lastname: Ponterini