Large Transmittance Change Induced by Exciton Accumulation under Weak Continuous Photoexcitation

Hirata, Shuzo; Vácha, Martin

doi:10.1002/adom.201500378

Cited by 15 publications

(17 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The large broadening is related largely to a saturation of p RTP intensity, which depends on excitation intensity. It has been reported that saturation occurs because of annihilation that is caused mainly by a singlet–triplet resonance energy transfer and a triplet–triplet resonance energy transfer because of a concentrated accumulation of triplet excitons in the materials. , In epifluorescent imaging with a resolution that approaches the diffraction limit, the excitation profile of the line width does not have a top-hat shape. Therefore, the emission profile has a center ((i) in Figure d) and tail parts ((ii) in Figure d).…”

Section: Resultsmentioning

confidence: 99%

Key of Suppressed Triplet Nonradiative Transition-Dependent Chemical Backbone for Spatial Self-Tunable Afterglow

Bhattacharjee

Hayashi

Hirata

2021

JACS Au

Self Cite

View full text Add to dashboard Cite

Highly efficient persistent (lifetime > 0.1 s) room-temperature phosphorescence ( p RTP) chromophores are important for futuristic high-resolution afterglow imaging for state-of-the-art security, analytical, and bioimaging applications. Suppression of the radiationless transition from the lowest triplet excited state (T 1 ) of the chromophores is a critical factor to access the high RTP yield and RTP lifetime for desirable p RTP. Logical explanations for factor suppression based on chemical structures have not been reported. Here we clarify a strategy to reduce the radiationless transition from T 1 based on chemical backbones and yield a simultaneous high RTP yield and high RTP lifetime. Yellow phosphorescence chromophores that contain a coronene backbone were synthesized and compared with yellow phosphorescent naphthalene. One of the designed coronene derivatives reached a RTP yield of 35%, which is the best value for chromophores with a RTP lifetime of 2 s. The optically measured rate constant of a radiationless transition from T 1 was correlated precisely with a multiplication of vibrational spin–orbit coupling (SOC) at a T 1 geometry and with the Franck–Condon chromophore factor. The agreement between the experimental and theoretical results confirmed that the extended two-dimensional fused structure in the coronene backbone contributes to a decrease in vibrational SOC and Franck–Condon factor between T 1 and the ground state to decrease the radiationless transition. A resolution-tunable afterglow that depends on excitation intensity for anticounterfeit technology was demonstrated, and the resultant chromophores with a high RTP yield and high RTP lifetime were ideal for largely changing the resolution using weak excitation light.

show abstract

Section: Resultsmentioning

confidence: 99%

Key of Suppressed Triplet Nonradiative Transition-Dependent Chemical Backbone for Spatial Self-Tunable Afterglow

Bhattacharjee

Hayashi

Hirata

2021

JACS Au

Self Cite

View full text Add to dashboard Cite

show abstract

“…Φ p (RT) of the C(C 6 H 5 ) 4 , Si(C 6 H 5 ) 4 , and Ge(C 6 H 5 ) 4 crystals in air were 3.1%, 5.1%, and 17%, respectively. We carefully measured Φ p (RT) and τ p (RT) because triplet accumulation by strong excitation intensity triggers fluorescence resonance energy transfer from S 1 to accumulated triplet excitons, phosphorescence resonance energy transfer from T 1 to accumulated triplet excitons, and triplet–triplet annihilation, which cause underestimation of Φ p (RT) and τ p (RT) . We confirmed that underestimation did not occur when 280 nm excitation light with a power of 1.0 mW cm −2 was used because linear increases of fluorescence and RTP were observed around this excitation intensity (Figure S2, Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

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

Hirata

2019

Advanced Science

Self Cite

View full text Add to dashboard Cite

Conjugated molecular crystals with persistent room‐temperature phosphorescence (RTP) are promising materials for sensing, security, and bioimaging applications. However, the electronic structures that lead to efficient persistent RTP are still unclear. Here, the electronic structures of tetraphenylmethane (C(C 6 H 5 ) 4 ), tetraphenylsilane (Si(C 6 H 5 ) 4 ), and tetraphenylgermane (Ge(C 6 H 5 ) 4 ) showing blue‐green persistent RTP under ambient conditions are investigated. The persistent RTP of the crystals originates from minimization of triplet exciton quenching at room temperature not suppression of molecular vibrations. Localization of the highest occupied molecular orbitals (HOMOs) of the steric and highly symmetric conjugated crystal structures decreases the overlap of intermolecular HOMOs, minimizing triplet exciton migration, which accelerates defect quenching of triplet excitons. The localization of the HOMOs over the highly symmetric conjugated structures also induces moderate charge‐transfer characteristics between high‐order singlet excited states (S m ) and the ground state (S 0 ). The combination of the moderate charge‐transfer characteristics of the S m –S 0 transition and local‐excited state characteristics between the lowest excited triplet state and S 0 accelerates the phosphorescence rate independent of the vibration‐based nonradiative decay rate from the triplet state at room temperature. Thus, the decrease of triplet quenching and increase of phosphorescence rate caused by the HOMO localization contribute to the efficient persistent RTP of Ge(C 6 H 5 ) 4 crystals.

show abstract

“…In materials with persistent RTP, the intensity of phosphorescence (the population of triplet states) gradually saturates as the excitation intensity increases . In the case of the CzDClT single crystal, intensity saturation of persistent RTP was observed when excitation intensity was above 0.01 mW cm −2 (Figure S6a, Supporting Information).…”

Section: Calculated Parameters Of Transfer Integral Reorganization Ementioning

confidence: 98%

Suppressed Triplet Exciton Diffusion Due to Small Orbital Overlap as a Key Design Factor for Ultralong‐Lived Room‐Temperature Phosphorescence in Molecular Crystals

et al. 2019

Self Cite

View full text Add to dashboard Cite

of intramolecular vibrational relaxation and the nonradiative rate (k q (RT)) of triplet quenching due to interactions with ambient surrounding are much larger than k p . Therefore, reports of RTP from metal-free aromatic molecules in ambient condition have been scarce. [8,9] However, in the past 5 years, RTP from metal-free aromatics under ambient conditions has been successfully realized by suppressing k nr (RT) + k q (RT) in various materials, such as host-guest systems, carbon nanodots, and aromatic crystals. [10][11][12][13][14][15][16] In some of these materials, ultralong-lived RTP (persistent RTP) has sufficient intensity and lifetime in air for an observation by naked eye after ceasing the irradiation. [12][13][14][15][16] Due to its ultralong lifetime at RT on the order of seconds, the detection of persistent RTP is not affected by autofluorescence or scattering of the excitation light, [17] and as such can be measured experimentally with low-cost detectors, thus fulfilling one of the requirements for application in bioimaging, optical sensing, and security. [18][19][20][21] For the appearance of persistent RTP under ambient conditions, high efficiency of intersystem crossing (ISC) from the lowest singlet excited state (S 1 ) to the lowest triplet excited state (T 1 ) and suppression of k nr (RT) + k q (RT) are crucial. Efficient ISC from S 1 to T 1 can be obtained by molecular design based on symmetry rules or the El-Sayed rule. [22][23][24] Therefore, the elucidation of the mechanism of suppression of k nr (RT) + k q (RT) is very important factor for persistent RTP. Some heavy atomfree conjugated molecules dispersed in polymers show weak persistent RTP under inert conditions because of the potential suppression of k nr (RT) + k q (RT). [25][26][27][28] However, the analysis of the mechanism of k nr (RT) and k q (RT) suppression was complicated because the experimental separation of the k nr (RT) component from k nr (RT) + k q (RT) was inconclusive. [29] On the other hand, in the case of host-guest systems, the separation of the two nonradiative processes k nr (RT) and k q (RT) was realized by introducing very rigid host matrix with high T 1 energy. The rigid matrix can suppress thermally activated energy transfer over large energy difference from guest molecules to the host and protect from oxygen, resulting in large decrease k nr (RT) + k q (RT) and leading to efficient persistent RTP under ambient conditions. [12] Later, experiments in such rigid hosts revealed that k nr (RT) and k p were intrinsically comparable, [24] Persistent room-temperature phosphorescence (RTP) under ambient conditions is attracting attention due to its strong potential for applications in bioimaging, sensing, or optical recording. Molecular packing leading to a rigid crystalline structure that minimizes nonradiative pathways from triplet state is often investigated for efficient RTP. However, for complex conjugated systems a key strategy to suppress the nonradiative deactivation is not found yet. Here, the origin of small ra...

show abstract

Large Transmittance Change Induced by Exciton Accumulation under Weak Continuous Photoexcitation

Cited by 15 publications

References 43 publications

Key of Suppressed Triplet Nonradiative Transition-Dependent Chemical Backbone for Spatial Self-Tunable Afterglow

Key of Suppressed Triplet Nonradiative Transition-Dependent Chemical Backbone for Spatial Self-Tunable Afterglow

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

Suppressed Triplet Exciton Diffusion Due to Small Orbital Overlap as a Key Design Factor for Ultralong‐Lived Room‐Temperature Phosphorescence in Molecular Crystals

Contact Info

Product

Resources

About