Understanding and Design Beyond Born-Oppenheimer using Time-Domain Vibrational Spectroscopy
Lead Research Organisation:
Newcastle University
Department Name: Sch of Natural & Environmental Sciences
Abstract
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People |
ORCID iD |
| Thomas Penfold (Principal Investigator) |
Publications
Ahmad S
(2022)
Rapid predictions of the colour purity of luminescent organic molecules
in Journal of Materials Chemistry C
Cao Y
(2019)
Excited State Intramolecular Proton Transfer Dynamics for Triplet Harvesting in Organic Molecules.
in The journal of physical chemistry. A
Dias F
(2017)
Photophysics of thermally activated delayed fluorescence molecules
in Methods and Applications in Fluorescence
Dos Santos PL
(2018)
Triazatruxene: A Rigid Central Donor Unit for a D-A3 Thermally Activated Delayed Fluorescence Material Exhibiting Sub-Microsecond Reverse Intersystem Crossing and Unity Quantum Yield via Multiple Singlet-Triplet State Pairs.
in Advanced science (Weinheim, Baden-Wurttemberg, Germany)
Eng J
(2019)
D-A 3 TADF emitters: the role of the density of states for achieving faster triplet harvesting rates
in Journal of Materials Chemistry C
Eng J
(2020)
Understanding and Designing Thermally Activated Delayed Fluorescence Emitters: Beyond the Energy Gap Approximation.
in Chemical record (New York, N.Y.)
Eng J
(2021)
Open questions on the photophysics of thermally activated delayed fluorescence
in Communications Chemistry
Eng J
(2020)
Competition between the heavy atom effect and vibronic coupling in donor-bridge-acceptor organometallics.
in Physical chemistry chemical physics : PCCP
Eng J
(2019)
On the geometry dependence of tuned-range separated hybrid functionals.
in Journal of computational chemistry
| Description | To date we have studied organic and organometallic have been studied. Both of these exhibit crucial vibrational degrees of freedom which promote TADF. In both cases we have been able to identify these develop an understanding of their TADF mechanism in the context of vibrational modes. Importantly, we have provided understanding of dynamical processes in the context of the spin-vibronic couplings that are activated by specific movements of the molecule. These movements have been reframed in terms of dynamo-phores, the dynamical version of a chromophore, and form the basis of a new modular approach for molecular design. In particular for the organic molecule by manipulating the density of states a triplet harvesting rate of 1.5 x10^7s-1 and PLQY~1 can been achieved: this is faster triplet harvesting than for Ir based metal-organic complexes. This molecule, TAT-3DBTO2 (Triazatruxene: A Rigid Central Donor Unit for a D-A3 Thermally Activated Delayed Fluorescence Material Exhibiting Sub-Microsecond Reverse Intersystem Crossing and Unity Quantum Yield via Multiple Singlet-Triplet State Pairs., Adv. Sci., 1700989 (2018).) comprising a rigid triazatruxenemulti-donorcoreand very stable dibenzothiophene-S,S-dioxide acceptors yields EQEmax > 30% in green devices with very low efficiency roll-off. Quantum chemistry and molecular dynamics simulations show that TAT-3DBTO2 is different from previous D-A-D molecules, having multi-resonant charge-transfer states, six pairs of S and T states lying within 0.3 eV, with multiple surface crossings that produces efficient rISC. However, while the initial rISC rate is very fast, secondary slower rISC channels (~10^5s-1 ) are present and contribute to poor roll performance. This is due to subtle excited state conformational dynamics. We have identified that relaxation of the D-A dihedral angle from the ground state 70 degs to near 90 degs in the excited state localises the excited CT states to the truxene and one acceptor with the other excited state remaining higher in energy. This reduces the advantageous high density of state, causing the rISC rate to slow down, again causing rISC rates dispersion even in 33RC, and making it more similar to typical D-A-D TADF molecules. For organometallic, we have studied the excited state properties and intersystem crossing dynamics of a series of donor-bridge-acceptor carbene metal-amides based upon the coinage metals Cu, Ag, Au, using quantum dynamics simulations and supported by photophysical characterisation. The simulated intersystem rates are consistent with experimental observations making it possible to provide a detailed interpretation of the excited state dynamics which ultimately control their functional properties. It is demonstrated that for all complexes there is a competition between the direct intersystem crossing occurring between the 1CT and 3CT states and indirect pathways which couple to an intermediate locally excited pp* triplet state (3LE) on either the donor or acceptor ligands. The energy of the 3LE states decreases as the size of the metal decreases meaning that the indirect pathway plays an increasingly important role for the lighter metals. Importantly whenever the direct pathway is efficient, the presence of indirect pathways is detrimental to the overall rate of ISC as they provide a slower alternative pathway. Our results provide a detailed insight into the mechanism of intersystem crossing in these complexes and will greatly facilitate the design of new higher performing molecules, but also provide the link between the organic and organometallic systems. Finally, the concepts of spin-vibronic coupling and ISC have been extended to spin changes in small molecular magnet materials. In this case, we have explored the dynamics occurring after photoexcitation of a trinuclear µ3-oxo-bridged Mn(iii)-based SMM, whose magnetic anisotropy is closely related to the Jahn-Teller distortion. Ultrafast transient absorption spectroscopy in solution reveals oscillations superimposed on the decay traces due to a vibrational wavepacket. Based on complementary measurements and calculations on the monomer Mn(acac)3, we conclude that the wavepacket motion in the trinuclear SMM is constrained along the Jahn-Teller axis due to the µ3-oxo and µ-oxime bridges. Our results provide new possibilities for optical control of the magnetization in SMMs on femtosecond timescales and open up new molecular-design challenges to control the wavepacket motion in the excited state of polynuclear transition-metal complexes. This final work has recently been published in Nature Chemistry (https://www.nature.com/articles/s41557-020-0431-6) |
| Exploitation Route | Through a new conceptual design of Thermally Activated Delayed Fluorescence (TADF) molecules, we have shown that it is possible to achieve both a reverse intersystem crossing (rISC) rate > 1x107 s-1 and a unity photoluminescence quantum yield (PLQY), a combination previously considered untenable. The difference in this new material is the high density of coupled excited states which enhances rISC through a spin-vibronic coupling mechanism. However, despite the rapid rISC this emitter is far from optimal and we have recently identified excited state conformational dynamics responsible for slower secondary channels, giving poor roll-off performance and degradation of the emitter. We are now seeking to exploit steric hindrance and non-covalent interactions to exert finer conformational control of the excited state dynamics to enhance functional properties. This is performed in conjunction with detailed studies to establish a deeper understanding of the excited states and their geometries formed by charge recombination. This proposal will deliver new understanding about the emission processes in TADF OLEDs and how to enhance the rISC rate to beyond 1x108 s-1 whilst retaining PLQY ~ 1. Achieving these outcomes will have a major disruptive impact on the OLED industry and ensure that the UK remains in the lucrative OLED materials supply chain. Aligned with these we are also seeking similar research programmes for the organometallic systems and the small molecular magnets. |
| Sectors | Electronics,Energy |
| URL | http://tompenfoldresearch.weebly.com/thermally-activated-delayed-fluorescence.html |
| Description | The results obtained have led to a CASE studentship and funding from Idemitsu Korsan. The objective is to develop the spin-vibronic concept developed to provide new understanding on the vibrational degrees of freedom which are important for performance, but also those which contribute width to the emission spectrum. In the context of OLEDs, it is crucial that the emission is narrow to achieve high colour purity. To develop this, we have established the key factors determining the emission full-width at half-maximum (FWHM) demonstrating that the emission FWHM can be interpreted within the displaced harmonic oscillator model (DHO), meaning that predictions can be made using ground state frequency and excited state gradient calculations only. This eliminates the need for time consuming calculations of excited state geometries and Hessians. While formally only valid within the Condon approximation, the DHO model provides reasonable correlations for spectra exhibiting significant Herzberg-Teller effects and not only makes it possible to predict emission FWHM, but also informs on the normal modes responsible for emission band broadening. |
| Sector | Energy |
| Impact Types | Economic |
| Description | Cynora GmBH, Germany: - Energy Transfer Processes |
| Amount | £37,635 (GBP) |
| Organisation | Cynora GmBH |
| Sector | Private |
| Country | Germany |
| Start | 01/2019 |
| End | 12/2019 |
| Description | PhD studentship Indemitsu |
| Amount | £26,000 (GBP) |
| Organisation | Idemitsu Kosan |
| Sector | Private |
| Country | Japan |
| Start | 09/2019 |
| End | 09/2022 |
| Title | A Quantum Dynamics Study on the Hyperfluorescence Mechanism |
| Description | Calculation outputs related to the papers;
A Quantum Dynamics Study on the Hyperfluorescence Mechanism README:: This dataset contains the following calculation outputs. -----------------------------Calculation on TBPe:----------------------------- Electronic Structure (#State refers to the electronic state of TBPe)-----------------------------Geometry optimisation outputs of TBPE:............OPTIMISATION_#State.outOptimised geometries of TBPe:.....................GEOMETRY_#State.xyzGround state frequencies output of TBPe:..........FREQUENCIES_S0.outElectronic structure calculation of TBPe:.........ELECTRONIC_STRUCTURE_#State.outGradient calculation output of TBPe:..............GRADIENT_#State.out Coupling calculations: (#Distance corresponds to the intermolecular distance/sqrt(3) )-----------------------------Electronic structure + FED couplings along the intermolecular distance:At the Au-Cz Co-planar geometry for Singlets:.....COUPLING-COPLANAR-R#Distance-SINGLETS.outAt the Au-Cz Co-planar geometry for Triplets:.....COUPLING-COPLANAR-R#Distance-TRIPLETS.outAt the Au-Cz Perpendicular geometry for Singlets:.COUPLING-PERPENDICULAR-R#Distance-SINGLETS.outAt the Au-Cz Perpendicular geometry for Triplets:.COUPLING-PERPENDICULAR-R#Distance-TRIPLETS.out Electronic structure + FED couplings along the Au-Cz Torsion \varphi: (#Angle refers to the values of \varphi)At a distance of 14 for Singlets:.................COUPLING-PHI#Angle-SINGLETS.outAt a distance of 14 for Triplets:.................COUPLING-PHI#Angle-TRIPLETS.out Electronic structure + FED couplings along \theta_i: (#Angle refers to the values of the theta angles)At a distance of 14 and the co-planar geometry:...COUPLING-THETAx-#Angle.outAt a distance of 14 and the co-planar geometry:...COUPLING-THETAy-#Angle.outAt a distance of 14 and the co-planar geometry:...COUPLING-THETAz-#Angle.out Dynamics:----------------------------- With the T1 TBPe state for different \varepsilon' values: (#Epsilon' refers to the value of epsilon')Operator files:...................................DYNAMICS_T1_#Epsilon'.opInput files:......................................DYNAMICS_T1_#Epsilon'.inp Without the T1 TBPe state for different energies of S1E: (#Epsilon refers to the value of epsilon)Operator files:...................................DYNAMICS_noT1_#Epsilon.opInput files:......................................DYNAMICS_noT1_#Epsilon.inp -----------------------------Calculation on TBRb:----------------------------- Electronic Structure (#State refers to the electronic state of TBRb)-----------------------------Geometry optimisation outputs of TBRb:............TBRb_OPTIMISATION_#State.outOptimised geometries of TBRb:.....................TBRb_GEOMETRY_#State.xyzGround state frequencies output of TBRb:..........TBRb_FREQUENCIES_S0.outElectronic structure calculation of TBRb:.........TBRb_ELECTRONIC_STRUCTURE_#State.outGradient calculation output of TBRb:..............TBRb_GRADIENT_#State.out Coupling calculations: (#Distance corresponds to the intermolecular distance/sqrt(3) )-----------------------------Electronic structure + FED couplings along the intermolecular distance:At the Au-Cz Co-planar geometry for Singlets:.....TBRb_COUPLING-COPLANAR-R#Distance-SINGLETS.outAt the Au-Cz Co-planar geometry for Triplets:.....TBRb_COUPLING-COPLANAR-R#Distance-TRIPLETS.outAt the Au-Cz Perpendicular geometry for Singlets:.TBRb_COUPLING-PERPENDICULAR-R#Distance-SINGLETS.outAt the Au-Cz Perpendicular geometry for Triplets:.TBRb_COUPLING-PERPENDICULAR-R#Distance-TRIPLETS.out Electronic structure + FED couplings along the Au-Cz Torsion \varphi: (#Angle refers to the values of \varphi)At a distance of 14 for Singlets:.................TBRb_COUPLING_PHI#Angle-SINGLETS.out |
| Type Of Material | Database/Collection of data |
| Year Produced | 2020 |
| Provided To Others? | Yes |
| URL | https://data.ncl.ac.uk/articles/dataset/A_Quantum_Dynamics_Study_on_the_Hyperfluorescence_Mechanism/... |
| Description | Industrial Collaboration Cynora GmBH |
| Organisation | Cynora GmBH |
| Country | Germany |
| Sector | Private |
| PI Contribution | CYNORA is a leading company in the development of highly ef?cient TADF OLED emitting materials for OLED displays. They have funded a PhD student to exploit the theoretical developments of the Penfold group within NECEM to establish new design routes for their materials. |
| Collaborator Contribution | Funding of a PhD student and contribution in kind in terms of time and materials shared. |
| Impact | Still ongoing |
| Start Year | 2018 |
| Description | Maximising the RISC II |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | This workshop is designed to allow people from a diverse range of backgrounds to learn, discuss and experience the development of the TADF mechanism and other related research. The workshop has been titled 'Maximising the rISC' for a number of reasons; firstly, the current accepted model is that reverse intersystem crossing is fundamental to the TADF process and secondly, it is hoped that this workshop will help maximise the exchange of knowledge, impact and the reach of everyone involved. The 2018 version attracted greater numbers than in 2016 and a wider variety of speakers that meant we could expand the event across two days and include a workshop dinner on the evening of the first night. We had talks from Prof. Chihaya Adachi, Prof. Christel Marian, Prof. Eli Zysman-Colman and Prof. Peter Gilch and also talks from early career researchers such as Dr Anastasiia Klimash and Dr Sandra Pluczyk. |
| Year(s) Of Engagement Activity | 2018 |
| Description | NON-ADIABATIC QUANTUM DYNAMICS: FROM THEORY TO EXPERIMENTS |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | The field of molecular quantum dynamics is undergoing rapid development due to an increase in computational power and the emergence of new methodologies (see state of the art). This is offering exciting new opportunities to calculate the quantum properties of matter. At present a key challenge for the molecular quantum dynamics community is to coordinate the efforts between a number of subgroups, each developing their specific theoretical methods. Although many methods have the same foundation, they differ in their approximations and algorithmic implementations, bringing their own particular advantages and drawbacks. It is important that these groups come together to exchange ideas and advance research in this area. Concurrently, the rapid development in time-resolved spectroscopies across a broad range of wavelengths has increased the information content available from experiment, but also the complexity. Now more than ever, we must seek a strong synergy between theory and experiment. Indeed detailed theoretical studies are often essential to provide a firm link between the spectroscopic observables and the underlying molecular structure and dynamics. Developing such synergy is the objective of the present workshop which will address the following key questions: • What are the methods' advantages and limitations? For example, how do they scale with dimensionality/temperature/electronic states? How rapidly does the calculation converge bf for different system parameters? • Do the methods provide a consistent description of dynamics and statistics? • Which research areas are presently most poorly described by theory/experiment? • How can experimentalists and theoreticians improve collaboration? To achieve these objectives we propose a format where invited speakers (theoreticians and experimentalists) will be asked to present lectures on the state-of-the-art in their specific area of expertise. Each lecture will be followed by discussion. At the end of each day, we will hold a detailed discussion on the synergy between the different theories and experimental techniques. This will be used to identify shortfalls and propose new objectives. A small number of contributed talks will be scheduled, covering topics related to the invited lectures. |
| Year(s) Of Engagement Activity | 2018 |
| URL | https://www.cecam.org/workshop-details/181 |
| Description | Pint of Science Public Lecture |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Public/other audiences |
| Results and Impact | ~100 people from a general public attended a public outreach talk in Energy Materials as part of the Pint of Science Event |
| Year(s) Of Engagement Activity | 2018 |
| Description | Youtube Video for Research |
| Form Of Engagement Activity | Engagement focused website, blog or social media channel |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | A youtube video outlining recent research has been made and published. |
| Year(s) Of Engagement Activity | 2018 |
| URL | https://www.youtube.com/watch?v=DtnU7_2z2rg&t=9s |