Suppressing molecular motions for enhanced room-temperature phosphorescence of metal-free organic materials

Abstract

Metal-free organic phosphorescent materials are attractive alternatives to the predominantly used organometallic phosphors but are generally dimmer and are relatively rare, as, without heavy-metal atoms, spin–orbit coupling is less efficient and phosphorescence usually cannot compete with radiationless relaxation processes. Here we present a general design rule and a method to effectively reduce radiationless transitions and hence greatly enhance phosphorescence efficiency of metal-free organic materials in a variety of amorphous polymer matrices, based on the restriction of molecular motions in the proximity of embedded phosphors. Covalent cross-linking between phosphors and polymer matrices via Diels–Alder click chemistry is devised as a method. A sharp increase in phosphorescence quantum efficiency is observed in a variety of polymer matrices with this method, which is ca. two to five times higher than that of phosphor-doped polymer systems having no such covalent linkage.

AIEgen with Fluorescence–Phosphorescence Dual Mechanoluminescence at Room Temperature

“…[1] Intrigued by their emission and related important applications,t he light-emitting processes have attracted much attention. [2] As for the EL process,the excitons originate from the electron and hole recombination, then 25 %singlets and 75 % triplets are formed. In the PL process,t he organic luminogens absorb photons and jump to the excited singlet state.T hen most of them return to the ground state through fluorescence or non-radiative transitions,h owever some of them could transition to the excited triplet state and undergo phosphorescence emission, for which, metals (for example,I r 3+ and Pt 2+ )o rs pecial organic moieties (for example,a romatic aldehydes,h eavy halogens,o rd euterated carbons) are generally required to enhance the transition of singlet-to-triplet states.…”

Roles of Localized Electronic Structures Caused by π Degeneracy Due to Highly Symmetric Heavy Atom‐Free Conjugated Molecular Crystals Leading to Efficient Persistent Room‐Temperature Phosphorescence

“…[59] The activation energy of triplet exciton migration is theoretically expressed as the sum of the reorganization energies of hole and electron transfer. [12,56,58,59,65,66] By using an exponential function at higher temperature for each crystal, k q (RT) of C(C 6 H 5 ) 4 , Si(C 6 H 5 ) 4 , and Ge(C 6 H 5 ) 4 crystals were quantified as 3.6 × 10 −1 , 2.6 × 10 −1 , and 3.5 × 10 −1 s −1 , respectively. Therefore, the larger increase of k nr (T ) + k q (T ) at higher temperature in Figure 2b was caused by the increase of k q (T ) triggered by triplet exciton migration and the smaller increase of k nr (T) + k q (T) at lower temperature was caused by the increase of k nr (T) depending on the intramolecular www.advancedscience.com vibrations of chromophores.…”

Enhancing the Kinetic Stability and Lifetime of Organic Light‐Emitting Diodes based on Bipolar Hosts by using Spiroconjugation

“…[22,23] Using DFT calculations, we investigate the DE 3 values of the ET 0 -HT 0 molecules as well as their first ionization potentials (IPs) ( Table S1). (Due to the spin statistics, electron-hole recombination process will lead to 75 % of triplet excited states formation, and 25 % of singlet excited states.)…”