Enhanced intersystem crossing in carbonylpyrenes

Rajagopal, Shinaj K.; Mallia, Ajith R.; Hariharan, Mahesh

doi:10.1039/c7cp04834c

Cited by 42 publications

(45 citation statements)

References 60 publications

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“…In accordance with the results by Kumar et al (1983), which were explained by El-Sayed's rule (Lower & El-Sayed, 1966), inter-system crossing (ISC) from singlet to triplet states, followed by non-radiative relaxation, was suggested as a reason for the weak PA luminescence. Enhanced ISC mechanism was also pointed out as very highly probable in the case of simple carbonylpyrenes in solution (Rajagopal et al, 2017). Another explanation proposed for the relatively ineffective luminescence of PA in solution was the proximity effect (Wassam & Lim, 1978a,b).…”

Section: Spectroscopic and Single-electron Propertiesmentioning

confidence: 94%

“…All these observations make PA a promising subject to investigate the changes induced in its spectroscopic properties by crystalline environment and its rearrangements induced by pressure. Another motivation comes from the fact that materials similar to PA, namely acetyl-and benzoyl-pyrenes, have recently been shown to be efficient luminescent dyes and promising candidates for molecular electronic components, both in solution and in the solid state (Rajagopal et al, 2014(Rajagopal et al, , 2016(Rajagopal et al, , 2017.…”

Section: Introductionmentioning

confidence: 99%

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Structure and piezochromism of pyrene-1-carbaldehyde at high pressure

Tchoń

Makal

2019

Acta Crystallogr Sect B

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The crystal structure of pyrene-1-carbaldehyde (PA), a model polyaromatic hydrocarbon, highly luminescent in the solid state and crystallizing in the triclinic system, has been re-determined at several pressures ranging from atmospheric up to 3 GPa using a diamond anvil cell. A 'multi-crystal' approach was used in crystal structure determination, significantly improving completeness of X-ray diffraction data attainable for such a low-symmetry system. The crystal structure consists of infinite -stacks of PA molecules with discernible dimers, which resemble aggregates formed by pyrene derivatives in solution as well as in the solid state. A series of measurements showed that the average inter-planar distance between individual molecules within -stacks decreases with pressure in the investigated range. This results in piezochromic properties of PA: a significant sample color change as well as a red-shift of fluorescence with pressure, as studied with UV-vis spectroscopy. Periodic DFT calculations allowed us to relate the variations in the crystal structure with pressure to the changes in the electronic structure of this material. research papers Acta Cryst. (2019). B75, 343-353 Tchoń and Makal Structure and piezochromism of pyrene-1-carbaldehyde 353

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Section: Spectroscopic and Single-electron Propertiesmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Structure and piezochromism of pyrene-1-carbaldehyde at high pressure

Tchoń

Makal

2019

Acta Crystallogr Sect B

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“…[ 19,20,26 ] Thus, the presence of oxygen functional groups in GQD may boost the interest in oxidative analysis, since it can contribute to more efficient triplet harvesting via modulation of singlet‐triplet energy splitting (∆ E ST ) due to n–π* transition of CO. [ 13,27 ]…”

Section: Figurementioning

confidence: 99%

Controllable Singlet–Triplet Energy Splitting of Graphene Quantum Dots through Oxidation: From Phosphorescence to TADF

et al. 2020

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Long‐lived afterglow emissions, such as room‐temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), are beneficial in the fields of displays, bioimaging, and data security. However, it is challenging to realize a single material that simultaneously exhibits both RTP and TADF properties with their relative strengths varied in a controlled manner. Herein, a new design approach is reported to control singlet–triplet energy splitting (∆EST) in graphene quantum dots (GQD)/graphene oxide quantum dots (GOQDs) by varying the ratio of oxygenated carbon to sp2 carbon (γOC). It is demonstrated that ∆EST decreases from 0.365 to 0.123 eV as γOC increases from 4.63% to 59.6%, which in turn induces a dramatic transition from RTP to TADF. Matrix‐assisted stabilization of triplet excited states provides ultralong lifetimes to both RTP and TADF. Embedded in boron oxynitride, the low oxidized (4.63%) GQD exhibits an RTP lifetime (τTavg) of 783 ms, and the highly oxidized (59.6%) GOQD exhibits a TADF lifetime (τDFavg) of 125 ms. Furthermore, the long‐lived RTP and TADF materials enable the first demonstration of anticounterfeiting and multilevel information security using GQD. These results will open up a new approach to the engineering of singlet–triplet splitting in GQD for controlled realization of smart multimodal afterglow materials.

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“…13 For this reasons, alternative methods to promote ISC, e.g. using a spin converter, 14 introduction of carbonyl groups, 15 radicalenhanced ISC 16 and twist-induced ISC 17 have been actively studied in recent years. However, it is still difficult to design heavy-atomfree sensitizers due to the lack of established relationships between ISC and molecular structure.…”

Section: Introductionmentioning

confidence: 99%