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

One bond 13C,13C- and 13C,1H-coupling constants have been measured for some 1,2-dimethylene-cycloalkanes, as well as for 2,3-dimethylbuta-1,3-diene and methylenecyclobutane. The results for 2,3-dimethylbuta-1,3-diene confirm the findings for buta-1,3-diene, i.e. that J(C-1, C-2) is smaller for the diene than for the correspondingly substituted monoene. No differences have been found between the 1J(CC) exocyclic coupling constants of the dimethylene and monomethylene cycloalkanes.

13C,13C coupling constants of conjugated dienes

MNDOC Calculations of the Potential Surfaces for Photochemical α-Cleavage†

Proton affinity of substituted naphthalenes

In nonadiabatic photoreactions in solution, the geometry at the decay region from the excited to the ground state is decisive for the outcome of the reaction. From a mechanistic point of view, this "reactive structun", is., the structure of the conical intersection accessible on the excited state of a singlet photoreaction or the region of geometries favorable for intersystem crossing in a triplet photoreaction, plays a similar role as the transition state in a thermal reaction. Consequences for the selectivity of singlet and triplet photoreactions are discussed.

Theoretical Models for the Selectivity of Organic Singlet and Triplet Photoreactions

The semiempirical MNDOC-CI method with CI limited to 100–500 selected configurations is well suited for computing excited state properties. Approximating energy gradients and second derivatives of the energy by finite differences and second differences of CI energies respectively, geometry optimization by the DFP method is achieved and vibrational frequencies can be calculated. Typical results are shown which were obtained by applying the method to ground and excited states of formaldehyde and to sudden polarization and TICT processes.

Martin Klessinger

Papers

13C,13C coupling constants of conjugated dienes

MNDOC Calculations of the Potential Surfaces for Photochemical α-Cleavage†

Proton affinity of substituted naphthalenes

Theoretical Models for the Selectivity of Organic Singlet and Triplet Photoreactions

Electronic structure and properties of molecules in excited states