Through-Space Conjugation: A Thriving Alternative for Optoelectronic Materials

Abstract

Efficient electronic coupling is the key to constructing optoelectronic functional π systems. Generally, the delocalization of π electrons must comply with the framework constructed by covalent bonds (typically σ bonds), representing classic through-bond conjugation. However, through-space conjugation offers an alternative that achieves spatial electron communication with closely stacked π systems instead of covalent bonds thus enabling multidimensional energy and charge transport. Because of the ever-accelerating advances of through-space conjugation studies, researchers are inspired greatly by the beauty of through-space conjugated systems and their potential in high-tech applications. In this mini review, we introduce some representative and newly developed π systems having the through-space conjugation feature. In addition to discussing the profound impacts of through-space conjugation on the luminescence properties and charge transport, we will review some impressive findings of distinctive molecules with attractive characteristics, such as aggregation-induced emission, thermally activated delayed fluorescence, bipolar charge transport, and multichannel. These achievements may bring about new breakthroughs of theory, materials, and devices in the fields of organic electronics and molecular electronics.

Aggregate Science: From Structures to Properties

“…[200] However, once clusters form in the aggregate state, the energy gap (∆E 2 and ∆E 3 ) become narrow because of the newly generated throughspace conjugation. [201][202][203][204][205][206][207][208] More specifically, the intermolecular interactions between molecules broaden the molecular energy levels such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) into electronic bands, i.e., conduction band (CB) and valance band (VB), which is similar to the quantum confinement effect in quantum dots. [209,210] The small energy gap (∆E 2 ) of loose clusters produce a visible clusteroluminescence located in the short-wavelength range.…”

Tuning the stability of organic radicals: from covalent approaches to non-covalent approaches

“…In this section, we will discuss p-p interaction and charge transfer interaction together because there should be partial delocalization of electrons between those stacking aromatic systems regardless of whether they are homogeneous or heterogeneous. 72 The interaction between radicals is somehow different from the conventional p-p interaction. There will be intermolecular spin-spin interaction between radicals which usually leads to the formation of high-spin species and a great effect on the stability of radicals.…”

Single White‐Emitting Polymers with High Efficiency, Low Roll‐Off, and Enhanced Device Stability by Using Through‐Space Charge Transfer Polymer with Blue Delayed Fluorescence as Host for Yellow Phosphor

“…Another possibility is that the blue TSCT emission can be enhanced in the aggregation state (Figure S7, Supporting Information), [ 5 ] which is in line with the PL spectra of P‐Ir6 measured in THF/water mixed solvents as proposed by Tang's group. [ 45–47 ] As shown in Figure 2c, the blue emission is gradually enhanced as the water fraction ( f w ) increases to form aggregates, with the intensity enhanced by ≈17 folds upon f w growing from 0 to 0.99. Interestingly, it is noted that the yellow emission of P‐Ir6 is also enhanced as f w increases, different from Ir(tptpy) 2 (acac) itself which behaviors as an aggregation‐induced quenching emitter (Figure 2d).…”