title: Intersystem crossing processes in nonplanar aromatic heterocyclic molecules.
abstract: A comprehensive study of the photophysical properties of a series of monoaza[5]helicenes is presented on the basis of joint optical spectroscopy and quantum chemistry investigations. The molecules have been characterized by absorption and CW/time-resolved luminescence measurements. All quantities related to spin-orbit-coupling processes, such as intersystem crossing rates and radiative phosphorescence lifetimes, were found to depend strongly on the nitrogen position within the carbon backbone. Density functional theory and semiempirical quantum-chemical methods were used to evaluate the molecular geometries, the characteristics of the excited singlet and triplet states, and the spin-orbit coupling matrix elements. We demonstrate that the magnitude of spin-orbit coupling is directly correlated with the degree of deviation from planarity. The trends from the calculated photophysical quantities, namely, radiative fluorescence and phosphorescence decay rates and intersystem crossing rates, of the mono-aza-helicenes are fully consistent with experiment.
authors.affiliation: School of Chemistry and Biochemistry and Center of Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
authors.forename: Karin
authors.initials: K
authors.lastname: Schmidt
authors.forename: Sergio
authors.initials: S
authors.lastname: Brovelli
authors.forename: Veaceslav
authors.initials: V
authors.lastname: Coropceanu
authors.forename: David
authors.initials: D
authors.lastname: Beljonne
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cornil
authors.forename: Cristina
authors.initials: C
authors.lastname: Bazzini
authors.forename: Tullio
authors.initials: T
authors.lastname: Caronna
authors.forename: Riccardo
authors.initials: R
authors.lastname: Tubino
authors.forename: Francesco
authors.initials: F
authors.lastname: Meinardi
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Shuai
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Brédas