Stereoisomer-Independent Stable Blue Emission in Axial Chiral Difluorenol

Bulky conjugated molecules with high stability are the prerequisite for the overall improvement of performance in wide-bandgap semiconductors. Herein, a chiral difluorenol, 2,2′-(9,9′-spirobi[fluorene]-2,2′-diyl)bis(9-(4-(octyloxy)phenyl)-9H-fluoren-9-ol) (DOHSBF), is set as a desirable model to reveal the stereoisomeric effects of wide-bandgap molecules toward controlling photophysical behavior and improving thermal and optical stability. Three diastereomers are obtained and elucidated by NMR spectra. Interestingly, the effect of modifying the stereo-centers is not observed on optical properties in solutions, pristine films, or post-treated film states. All three diastereomers as well as the mixture exhibit excellent spectral stability without undesirable green emission. Therefore, this stereoisomer-independent blue-emitting difluorenol will be a promising candidate for next-generation wide-bandgap semiconductors that would have extensive application in organic photonics.

A Unified Framework for Photophysical Rate Calculations in TADF Molecules

One of the challenges in organic light emitting diodes research is finding ways to increase device efficiency by making use of the triplet excitons that are inevitably generated in the process of electroluminescence. One way to do so is by thermally activated delayed fluorescence, a process in which singlet excitons undergo up-conversion to singlet states, allowing them to relax radiatively. The discovery of this phenomenon has ensued a quest for new materials that are able to effectively take advantage of this mechanism. From a theoretical standpoint, this requires the capacity to estimate the rates of the various processes involved in the photophysics of candidate molecules, such as intersystem crossing, reverse intersystem crossing, fluorescence and phosphorescence. Here we present a method that is able to, within a single framework, compute all these rates and predict the photophysics of new molecules. We apply the method to two TADF molecules and show that results compare favorably with other theoretical approaches and experimental results. Finally, we use a kinetic model to show how the calculated rates act in concert to produce different photophysical behavior.

A Unified Framework for Photophysical Rate Calculations in TADF Molecules

One of the challenges in organic light emitting diodes research is finding ways to increase device efficiency by making use of the triplet excitons that are inevitably generated in the process of electroluminescence. One way to do so is by thermally activated delayed fluorescence, a process in which singlet excitons undergo up-conversion to singlet states, allowing them to relax radiatively. The discovery of this phenomenon has ensued a quest for new materials that are able to effectively take advantage of this mechanism. From a theoretical standpoint, this requires the capacity to estimate the rates of the various processes involved in the photophysics of candidate molecules, such as intersystem crossing, reverse intersystem crossing, fluorescence and phosphorescence. Here we present a method that is able to, within a single framework, compute all these rates and predict the photophysics of new molecules. We apply the method to two TADF molecules and show that results compare favorably with other theoretical approaches and experimental results. Finally, we use a kinetic model to show how the calculated rates act in concert to produce different photophysical behavior.

Mesomorphic Behavior of Symmetric Azomethine Dimers Containing Different Chromophore Groups

A series of new azomethine dimers was synthesized by the condensation reaction of flexible bis-benzaldehydes with four aromatic amines containing phenyl, naphthyl, anthracene and pyrene groups. Their right structure was confirmed by FTIR and 1H-NMR spectroscopy and their thermal properties were investigated by thermogravimetric analysis, differential scanning calorimetry and polarized light optical microscopy. A view on their photophysical behavior was gained by UV-vis and photoluminescence spectroscopy. The dimers containing pyrene and anthracene presented liquid crystalline behavior, while the other dimers were crystalline compounds. Two dimers containing pyrene moieties formed mesomorphic glasses and had intense luminescence, promising properties for applications in building optoelectronic devices.