讲座预告 | Madrid Institute for Advanced Studies - IMDEA Nanoscience Johannes Gierschner 教授 系列报告

Emission Color Pureness and Efficiency Regulation 

in Organic Chromophores

Luminescent conjugated organic chromophores have found immense interest in current materials research, and rapid progress has been seen over the past years. In any case, the quest for sustainable research demands pre-synthesis tailor-made targeted design beyond experimental (and computational) trial-and-error strategies. This can only be achieved by a thorough understanding of the underlying photophysical process combined with spectroscopic and computational techniques. In this spirit, the seminar will focus on key parameters of emissive organic materials, being (1) luminescence efficiency and (2) color purity, being both crucial in particular for OLED research. 

(1) Luminescence efficiency is decided by the competition of radiative vs. nonradiative processes. Nonradiative decay via internal conversion (IC) is frequently tackled via 'Fermi's Golden Rule' (FGR).[1] However, in particular for systems with very effective IC, FGR may break down both in a quantitative and qualitative manner. This was especially shown for compound families which establish an 'inverted energy gap law', sharply contrasting the prediction of FGR. Instead, this has to be treated via conical intersections (CIs). In the solid state, IC becomes often a minor pathway, as the access to the CI often involves large amplitude motions,[2,3] giving rise to 'Solid State Luminescence Enhancement' (SLE).[1] On the other hand, examples of active CIs in solid state samples have been identified, due to the absence of large amplitude motions on the path to the CI,[4] so that fluorescence quenching persists in molecular solids. 

(2) Color purity, i.e. measured by the effective spectral width,[5] can be conveniently predicted within commercial quantum chemistry program packages; however; while this generates quite accurate numbers, it does not provide understanding. We will show that such understanding ‒ 'beyond numbers' ‒ can be achieved at a simple conceptual basis using resonance theory and MO topology consideration; this allows for targeted 'paper and pencil' molecular design of color pure emitters, ranging from the UV to blue region[5] to the deep red/NIR.[6]

References

[1] For a recent review on this matter, see J. Gierschner et al, , Adv. Opt. Mater. 2021, 9, 2002251.

[2] (a) J. Shi et al, J. Phys. Chem. C 2017, 121, 23166; (b) J. Shi et al, Org. Chem. Front. 2019, 6, 1948; (c) M. A. Izquierdo et al, Phys. Chem. Chem. Phys. 2019, 21, 22429.

[3] Y. Feng et al, Angew. Chem. Int. Ed. 2025, 137, e202416425.

[4] J.-M. Heo et al, Nat. Commun. 2025, 15, 5560.

[5] (a) S. Song et al, Adv. Mater. 2024, 36, 2404388; (b) S. Song et al, Tetrahedron 2025, 175, 134522.

[6] M. Eskandari et al, J. Phys. Chem. A 2025, 129, 1599.

Charge Transfer State Engineering for 

Tailor-Made Luminescent Organic Materials

In the past 20 years, all-organic chromophores were intensively investigated for application in materials conversion and life science applications. For the different purposes, color-specific, luminescent or non-luminescent, dissolved or aggregated chromophores are targeted. In order to achieve this, increasingly complex multi-channel photophysics are exploited, such as dual emission (DE), photoinduced electron transfer (PeT), RTP, TADF, TICT, or SLE/AIE in co-/crystals.[1] Charge transfer (CT) states play a central role in most of these processes. Tailor-made design of such compounds is thus of high technological demand; it requires, however, a detailed understanding to ultimately control the multiple deactivation processes, inter alia modulated by inter-chromophore interactions. The complexity of the underlying processes and their pivotal importance for materials' performance poses however grand challenges; in fact, misconceptions and false claims are frequently and increasingly found in this vivid area of research. A breakthrough in targeted design can be therefore only achieved in a holistic manner, combining advanced spectroscopic and computational methods in an intimate interdisciplinary 'dual expertise' scheme, in fact followed in our group.

The seminar will give insight to our recent activities to decipher complex photophysics of organic materials involving CT states. This will include (i) exciplex-forming DE donor-acceptor triads for stimuli-responsive materials,[2] (ii) perylene-based deep-red solid state emitters through PeT regulation,[3] (iii) efficient TADF emitters for OLED vs. photocatalysis applications,[4] and (iv) solid state color regulation by intra- vs. intermolecular charge transfer (CT) states.[5] Following an overview on these processes, we will detail selected examples to illustrate the in-depth analysis procedure.

References

[1] For recent reviews, see (a) Dual Emission: Classes, Mechanisms and Conditions, S. K. Behera et al, Angew. Chem. Int. Ed. 2021, 60, 22624.; (b) Luminescence in Crystalline Organic Materials: From Molecules to Molecular Solids, J. Gierschner et al, Adv. Opt. Mater. 2021, 9, 2002251.

[2] S. Feng et al, Adv. Mater. 2023, 35, 2306678.

[3] N. Tang et al, Nat. Commun. 2023, 14, 1922.

[4] (a) V. K. Singh et al, Nat. Catal. 2018, 1, 794-804.; (b) Y. Kwon et al, Nat. Commun. 2023, 14, 92; (c) Y. Kwon et al, Nat. Commun. 2024, 15, 2829; (d) Y. Kwon et al, Acc. Chem. Res. 2025, 58, 1581.

[5] (a) S. K. Park et al, J. Am. Chem. Soc. 2013, 135, 4757; (b) M. Wykes at al, J. Phys. Chem. Lett. 2015, 6, 3682; (c) S. K. Park et al, Angew. Chem. Int. Ed. 2016, 55, 203; (d) S. Oh et al, J. Phys. Chem. C 2020, 37, 20377; (e) I. Bhattacharjee et al, to be submitted.

Johannes Gierschner received his Ph.D. in Physical Chemistry at the Univ. Tübingen, Germany, in 2000. After stays at Univ. Tübingen, at the Univ. of Mons (Belgium), and at Georgia Tech, Atlanta (USA), he joined the Madrid Institute for Advanced Studies - IMDEA Nanoscience - in 2008 as a Senior Research Professor (Ramón y Cajal fellow 2008-13). In 2014, he habilitated at Tübingen and holds an Adjunct Prof. position ('Privatdozent') there since then. 

JG is regular visiting researcher at Univ. Valencia (since 2014), and at Seoul National University (SNU; since 2008), and held Visiting Professor positions at SNU and Univ. Mons (2014/15). His 160 papers integrate optical spectroscopy and computational chemistry to elucidate structure-property and -process relationships in conjugated organic materials for optoelectronics and energy conversion.

JG is further dedicated to consolidate the community knowledge through regular educative reviews, and international lecture series in 'Photophysics of Conjugated Organic Materials'. Moreover, during the last years, he is increasingly committed to 'Scientific Integrity' issues below the tip of the iceberg, providing seminars for junior and senior researchers.