In the present feature article, we present the new generations of spirobifluorenes for organic electronics and we detail the impact of positional isomerism on the electronic properties and device performance.

Intramolecular excimer emission arising from organic molecules as a blue light source in fluorescent Small Molecule Organic Light Emitting Diodes (SMOLEDs) is almost absent from the literature. In this work, three aryl-substituted DiSpiroFluorene–IndenoFluorenes (DSF–IFs 1–3) possessing different fluorescent properties due to their different main emitters have been investigated through a structure–property relationship study. Due to its particular geometry, the rigid DSF–IF platform 2 allows an ‘aryl/fluorene/aryl’ dimer to be preformed in the ground state leading, in the excited state, to a deep blue fluorescent emission through strong π–π intramolecular interactions between the two ‘aryl/fluorene/aryl’ arms. 2 has been successfully used as an emitting layer in a SMOLED with electroluminescence arising from electrogenerated intramolecular excimers and the properties of these excimer-based OLEDs have been compared to those of two model compounds (1 and 3). The simple and non-optimized double-layer device displays a deep blue colour (CIE coordinates: 0.19; 0.18) exhibiting a luminance of 510 Cd m⁻² with a luminous efficiency of ca. 0.1 Cd A⁻¹. This work is, to the best of our knowledge, the first rational and comparative study describing an intramolecular excimer based-SMOLED.

We report herein a new pure hydrocarbon material, 4-phenyl-9,9′-spirobifluorene (4-Ph-SBF), with a high triplet energy level (E_T: 2.77 eV) as a host for blue phosphorescent organic light-emitting diodes (PhOLEDs). Structural, thermal, electrochemical and photophysical properties have been investigated in detail and compared to its constituting building block 9,9′-spirobifluorene (SBF) in order to precisely study the influence of the incorporation of a phenyl unit in C4. A surprising out of plane deformation of the fluorene ring and a highly twisted structure have been notably found for 4-Ph-SBF due to the substitution in C4. As both 4-Ph-SBF and SBF possess a high triplet energy level (2.77/2.87 eV resp.), they have been successfully used as host materials for green and blue PhOLEDs. The performance of blue PhOLEDs, ca. 20 cd A⁻¹, appears to be among the highest reported for pure hydrocarbon derivatives.