Achieving Purely Organic Room-Temperature Phosphorescence Mediated by a Host–Guest Charge Transfer State

Abstract

Strategies for developing purely organic materials exhibiting both high efficiency and persistent room-temperature phosphorescence (RTP) have remained ambiguous and challenging. Herein, we propose that introducing an intermediate charge transfer (CT) state into the donor–acceptor binary molecular system holds promise for accomplishing this goal. Guest materials showing gradient ionization potentials were selected to fine-tune the intermolecularly formed CT state when doped into the same host material with a large electron affiliation potential. Such a CT intermediate state accelerates the population of the triplet exciton to benefit phosphorescent emission and decreases the phosphorescence lifetime via quenching the long-lived triplet excitons. As a result, a “trade-off” between a long phosphorescence lifetime (595 ms) and a high phosphorescent quantum yield (27.5%) can be obtained by tuning the host–guest energy gap offset. This finding highlights the key role of CT in RTP emission and provides new guidance for developing novel RTP systems.

Activating room-temperature phosphorescence of 1,8-naphthalimide by doping into aromatic dicarboxylic acids

“…With the aim of further enhancing the phosphorescent lifetime and/or prolonging the phosphorescent quantum yield of organic phosphors, organic–organic and organic–polymer guest–host RTP materials, using an effective doping strategy, have also been developed rapidly. 9–13…”

Base‐Tuning HOF‐Based Host–Guest Ultralong Organic Phosphorescence Systems with Phosphorescent Thermochromism Using for Information Security and Thermometer

“…For Ma&Ct, several S n (4.472−4.602 eV) and T n (3.234−4.612 eV) states of Ct monomer and Ma/Ct dimer are all lower than T 1 (4.727 eV) state of Ma molecule (Table S8, Supporting Information), suggesting that the intermolecular triplet‐to‐singlet FRET (FRET S‐T ) can occur from T 1 state of Ma molecule to S n states of Ct monomer and Ma/Ct dimer, [ 15 ] and triplet‐to‐triplet Dexter ET can conduct from T 1 states of Ma molecule to T n states of Ct monomer and Ma/Ct dimer (Figure 3e). [ 5,16 ] Because the singlet‐triplet energy gap (ΔE ST = 0.034 eV) of Ma/Ct dimer is smaller than that (0.046 eV) of Ct monomer, and SOC value [ξ(T 2 −S 1 ) = 6.748 cm –1 ] of Ma/Ct dimer is higher than that [ξ(T 2 –S 1 ) = 6.042 cm –1 ] of Ct monomer (Figure 3c,d; Table S9, Supporting Information), the high SOC value of RTP materials will result in the strong phosphorescence intensity, [ 4c,12b ] thus the sky‐blue phosphorescence of Ma/Ct dimer plays a major role in Ma&Ct system at room temperature. And the doping of Ct into Ma host leads to the blue shift of phosphorescence for Ma host.…”

“…[ 2 ] Various tuning strategies by reducing energy gap of S 1 state and low‐lying T n state, enhancing spin‐orbit coupling (SOC) value, increasing and changing energy transfer pathway have been successively proposed, thus the methods to design and fabricate UOP materials such as host–guest doping, H‐aggregation, polymerization, metal–organic frameworks, halogen bonding interactions and heavy atom effect are adopted, [ 3 ] of which the host–guest doping is popular because of its inherent advantages of low‐cost, facile preparation, controllable molecule structures and electronic properties. [ 4 ] However, the selection of host materials mostly focuses on triphenyl‐phosphine, β‐cyclodextrin, cyanuric acid, and triphenylamine based on trace doping of guest fillers, [ 5 ] new host system is expectantly to be discovered.…”

Broad‐Band Visible‐Light Excitable Room‐Temperature Phosphorescence Via Polymer Site‐Isolated Dye Aggregates

“…Purely organic room-temperature phosphorescent dyes are excellent alternative for heavy-metal based complexes in applications such as optical sensing, [1] imaging, [2] display, [3] and encryption [4,5] since heavy metal ions show substantial environmental toxicity. [6,7] However, organic RTP dyes usually exhibit much larger Stokes shifts [8][9][10][11][12] compared to the organometallic counterparts, which are capable of absorbing visible light due to a "semiallowed" charge-transfer state [13] involving d electrons with relatively high ground-state energy. The disparity between absorption and emission photon energies often leads to an unwanted situation where UV light irradiation is required even for red or near-infrared (NIR) RTP.…”