Excitation‐Dependent Multicolour Luminescence of Organic Materials: Internal Mechanism and Potential Applications

Abstract

Excitation-dependent emission (Ex-de) materials have been of considerable academic interest and have potential applications in real life. Such multicolour luminescence is a characteristic exception to the ubiquitously accepted Kasha's rule. This phenomenon has been increasingly presented in some studies on different luminescence systems; however, a systematic overview of the mechanisms underlying this phenomenon is currently absent. Herein, we resolve this issue by classifying multicolour luminescence from single chromophores and dual/ternary chromophores, as well as multiple emitting species. The underlying processes are described based on electronic and/or geometrical conditions under which the phenomenon occurs. Before we present it in categories, related photophysical and photochemical foundations are introduced. This systematic overview will provide a clear approach to designing multicolour luminescence materials for special applications.

Imaging of intracellular protein aggregates through plasmon-assisted clusteroluminescence

“…According to Kasha's rule, luminescence happens from the lowest excited state, and the emission wavelength is constant for a particular molecule with a definite structure, due to which the change in excitation will only result in a change in the emission intensity but not the emission wavelength. 57 However, in the case of clusteroluminescence, the electron delocalization differs in the clustered state, resulting from the different energy gaps of the emitters. These results confirm the emergence of clusteroluminescence from the protein–nanoparticle aggregates.…”

The magic of biaryl linkers: the electronic coupling through them defines the propensity for excited-state symmetry breaking in quadrupolar acceptor–donor–acceptor fluorophores

“…Slow relaxation to the lowest excited state and/or fast competing processes from the upper states lead to “anti-Kasha” behaviour. 82,83 Kasha–Vavilov rule, however, does not preclude the occurrence of the relatively slow processes from the upper states. Because of their relatively low probability, such slow processes usually have negligibly small and undetectable contributions to the observed photophysics.…”

Switching the Solid-State Emission of Organic Crystals through Coformer Choice and Vapochromism

“…Organic luminescent materials provide the advantages of broad structural tunability, ease of structural tailoring, bottom-up fabrication, and easy solution fabrication compared to their inorganic counterparts and therefore are vigorously perceived for their intriguing optoelectronic properties . The development of multicolour emissive and optoelectronic organic materials is an important but challenging area for which different approaches are being utilized . Polymorphism and cocrystal development represent two major crystal engineering approaches for the preparation of these materials.…”

“…35 The development of multicolour emissive and optoelectronic organic materials is an important but challenging area for which different approaches are being utilized. 36 Polymorphism and cocrystal development represent two major crystal engineering approaches for the preparation of these materials. Though the desired development of polymorphic materials is more challenging, they are crucial to understanding the structure− property relationship for prospective design and development.…”