Research Progress of Intramolecular π‐Stacked Small Molecules for Device Applications

Abstract

Organic semiconductors can be designed and constructed in π‐stacked structures instead of the conventional π‐conjugated structures. Through‐space interaction (TSI) occurs in π‐stacked optoelectronic materials. Thus, unlike electronic coupling along the conjugated chain, the functional groups can stack closely to facilitate spatial electron communication. Using π‐stacked motifs, chemists and materials scientists can find new ways for constructing materials with aggregation‐induced emission (AIE), thermally activated delayed fluorescence (TADF), circularly polarized luminescence (CPL), and room‐temperature phosphorescence (RTP), as well as enhanced molecular conductance. Organic optoelectronic devices based on π‐stacked molecules have exhibited very promising performance, with some of them exceeding π‐conjugated analogues. Recently, reports on various organic π‐stacked structures have grown rapidly, prompting this review. Representative molecular scaffolds and newly developed π‐stacked systems could stimulate more attention on through‐space charge transfer the well‐known through‐bond charge transfer. Finally, the opportunities and challenges for utilizing and improving particular materials are discussed. The previous achievements and upcoming prospects may provide new insights into the theory, materials, and devices in the field of organic semiconductors.

Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes

“…Nevertheless, the multiple-resonance (MR) induced TADF (MR-TADF) effect with the B/N doped polycyclic fused aromatic structure provides the possibility of constructing helicene-Page 2 of 16 CCS Chemistry 3 based purely organic TADF emitters. [17][18][19][20][21][22][23][24][25] On the one hand, the complementary resonance effects of the electron-deficient B and electron-rich N/O atoms can effectively separate the frontier molecular orbitals (FMOs), which induces the short-range charge transfer to achieve a small ΔE ST for efficient TADF. [26][27][28] On the other hand, from the perspective of chemical structure, the inherent fused aromatic structures of MR-TADF effect represent a perfect platform for constructing heterohelicenes, which excludes the use of D/A units.…”

Efficient narrowband electroluminescence based on a hetero-bichromophore thermally activated delayed fluorescence dyad

“…Commercial organic light-emitting diode (OLED) technology requires a high device efficiency, good color purity, and a long device lifetime simultaneously. [1][2][3][4][5] In the past decade, thermally activated delayed fluorescence (TADF) OLEDs have already demonstrated their potential as the third generation of OLEDs due to their 100% exciton utilization and low cost. In a TADF molecule, the small energy splitting between the lowest excited singlet (S 1 ) and triplet (T 1 ) states, DE ST , provides a practical pathway for harvesting non-emissive triplet excitons through the spin-flipping reverse intersystem crossing (RISC) process.…”

A reverse intersystem crossing managing assistant dopant for high external quantum efficiency red organic light-emitting diodes

“…However, the design of the TADF assistant dopant to effectively harvest the singlet excitons of a fluorescent emitter is still limited and further exploration of TADF materials is demanded. 16–25…”