The design and characterization of thermally activated delayed fluorescence (TADF) materials for optoelectronic applications represents an active area of recent research in organoelectronics. Noble metal-free TADF molecules offer unique optical and electronic properties arising from the efficient transition and interconversion between the lowest singlet (S1) and triplet (T1) excited states. Their ability to harvest triplet excitons for fluorescence through facilitated reverse intersystem crossing (T1→S1) could directly impact their properties and performances, which is attractive for a wide variety of low-cost optoelectronic devices. TADF-based organic light-emitting diodes, oxygen, and temperature sensors show significantly upgraded device performances that are comparable to the ones of traditional rare-metal complexes. Here we present an overview of the quick development in TADF mechanisms, materials, and applications. Fundamental principles on design strategies of TADF materials and the common relationship between the molecular structures and optoelectronic properties for diverse research topics and a survey of recent progress in the development of TADF materials, with a particular emphasis on their different types of metal-organic complexes, D-A molecules, and fullerenes, are highlighted. The success in the breakthrough of the theoretical and technical challenges that arise in developing high-performance TADF materials may pave the way to shape the future of organoelectronics.

Thermally Activated Delayed Fluorescence Materials Towards the Breakthrough of Organoelectronics

Prediction of molecular properties and molecular spectroscopy with density functional theory: From fundamental theory to exchange-coupling

Potential energy surface crossings in organic photochemistry

Carbohydrate structural determination by NMR spectroscopy: modern methods and limitations

Many light-induced molecular processes involve a change in spin state and are formally forbidden in non-relativistic quantum theory. To make them happen, spin–orbit coupling (SOC) has to be invoked. Intersystem crossing (ISC), the nonradiative transition between two electronic states of different multiplicity, plays a key role in photochemistry and photophysics with a broad range of applications including molecular photonics, biological photosensors, photodynamic therapy, and materials science. Quantum chemistry has become a valuable tool for gaining detailed insight into the mechanisms of ISC. After a short introduction highlighting the importance of ISC and a brief description of the relativistic origins of SOC, this article focusses on approximate SOC operators for practical use in molecular applications and reviews state-of-the-art theoretical methods for evaluating ISC rates. Finally, a few sample applications are discussed that underline the necessity of studying the mechanisms of ISC processes beyond qualitative rules such as the El-Sayed rules and the energy gap law. © 2011 John Wiley & Sons, Ltd.

Spin–orbit coupling and intersystem crossing in molecules

Results of semiempirical MN-DOC-CI and ab initio CASSCF calculations reveal that fulvene is a primary product of the photolysis of benzene. The photochemical step is assumed to lead to prefulvene, and both a synchronous conversion and a two-step process via bicyclo[3.1.0]hexa-1,3-diene (isofulvene) could be ruled out as possible pathways from prefulvene to benzene. The most probable mechanism for the photochemical isomerization of benzene to fulvene involves the intermediate structures prefulvene and 1,3-cyclopentadienylcarbene and has to compete with the almost barrierless formation of benzvalene and rearomatization to benzene. The short-lived intermediates are rather flexible structures with negligible barriers to inversion at the radical center in the threemembered ring of prefulvene and prebenzvalene and to rotation around the exocyclic single bond in 1,3-cyclopentadienylcarbene.

The photochemical Formation of Fulvene from Benzene via Prefulvene–a Theoretical Study

Ionisationspotentiale substituierter Benzole

The KDB energy level counting algorithm [M. J. H. Kemper, J. M. F. Van Dijk, and H. M. Buck, Chem. Phys. Lett., 53, 21 (1978)] has been modified such as to generate simultaneously the internal energy levels in two different states. Such algorithms are necessary for a description of the temperature dependence of the rotovibronic fine structure of electronic transitions as well as the rotatory fine structure of vibrational spectra. The performance of two versions of the algorithms as well as extensions to restrict the generation scheme to selected modes are discussed. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1312–1319, 1997

Martin Klessinger

Papers

The photochemical Formation of Fulvene from Benzene via Prefulvene–a Theoretical Study

Ionisationspotentiale substituierter Benzole

Algorithms for exact counting of energy levels of spectroscopic transitions at different temperatures

The photochemical formation of fulvene from benzene via prefulvene : a theoretical study

Konische Durchdringungen und der Mechanismus von Singulett-Photoreaktionen