Fabrice Mathevet

The development of efficient UV organic solid‐state lasers (OSLs) remains a significant challenge, yet it is crucial for enabling advanced photonic technologies. This study investigates two dispirofluorene‐indenofluorene regioisomers, (2,1‐a)‐DSF(tBu) ₄ ‐IF ( DSFIF‐syn ) and (1,2‐b)‐DSF(tBu) ₄ ‐IF ( DSFIF‐anti ), to elucidate the impact of subtle structural differences on their solid‐state photophysical and lasing properties. Through a combination of experimental techniques and theoretical approaches, including comprehensive optical characterization and molecular dynamics simulations, it is demonstrated that DSFIF‐syn exhibits significantly reduced intermolecular aggregation compared to DSFIF‐anti , resulting in enhanced optical performance in solid‐state thin films. Remarkably, amplified spontaneous emission (ASE) is achieved at a record‐short wavelength of 365 nm with a low threshold of 4.5 µJ cm ⁻² (5000 W cm ^{− 2} ) in a PMMA blend film. Moreover, distributed feedback (DFB) laser devices incorporating a blend film of DSFIF‐syn dispersed in polystyrene (PS) enabled lasing at an unprecedentedly short wavelength of 358.5 nm, as well as a low lasing threshold of 0.7 µJ cm ^{− 2} (780 W cm ^{− 2} ) at 363.3 nm. These results demonstrate that dispirofluorene‐indenofluorene derivatives are highly promising UV laser dyes, highlighting isomeric control as a valuable molecular design strategy for advancing high‐performance organic lasers.

We have examined the structural and electron transport properties of a swallow-tailed N,N'-bis(1-heptyloctyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI-C8,7) in thin films. A comprehensive analysis of material with the use of X-ray scattering methods evidenced the appearance of a new soft-crystalline mesophase that was induced by thermal processing of the swallow-tail PDI derivative. By combining electrical measurements with grazing-incidence wide-angle X-ray scattering (GIWAXS), we show that these morphological changes of thin films boost their charge transport in the organic field-effect transistor (OFET) configuration. The systematic device engineering of OFETs, including device architecture, thermal history, and preparation method of the active layer, resulted in a significant improvement in the electron field-effect mobility and the related performance parameters. In particular, the results demonstrate a strong improvement in the charge transport of PDI-C8,7 films in their soft-crystalline phase, which originates from the N-substitution by swallow-tails. In addition, our study demonstrates that the melt-processing route, a solvent-free and vacuum-free method for the fabrication of organic thin films, represents an efficient strategy for the fabrication of high-performance air-stable n-type OFETs.

Herein, we report the first example of chiral donor–acceptor cage DA-2 displaying efficient circularly polarized thermally activated delayed fluorescence (CP-TADF) with | g _lum | values up to 2.1 × 10 ⁻³ and PLQY of 32%.

2D organic–inorganic perovskites are an emerging class of materials with great potential for optoelectronics since a wide variety of large functional chromophores can be regularly incorporated. Among this new type of materials, hybrid perovskite systems incorporating strong electron acceptor molecules are considered as a promising approach to designing a new type of functional 2D perovskites for optoelectronics. In this work, a rare example of organic–inorganic 2D perovskite incorporating strong acceptors such as naphthalene diimide (NDI) building blocks between inorganic sheets is presented. This hybrid architecture forms highly air‐stable thin films with a structure consisting of inorganic perovskite monolayers of metal‐halide octahedra separated by bilayers of NDI‐based organic cations. The presence of strong electron‐accepting moieties in this multifunctional donor–acceptor hybrid heterostructure leads to a rare type II heterojunction in which the excitons can be efficiently dissociated via the electron‐transfer process and in which holes and electrons can be easily confined in the inorganic and organic sublayers, respectively. Such an ultimate p–n heterojunction shows improved photoconduction properties with a photocurrent multiplied by ≈40 under white‐light illumination in comparison to a similar 2D perovskite structure containing optically and electrically inert alkyl chains as organic components.

We show that through the introduction of short dimethylsiloxane chains, it was possible to suppress the crystalline state of CBP in favor of various types of organization, transitioning from a soft crystal to a fluid liquid crystal mesophase, then to a liquid state. Characterized by X-ray scattering, all organizations reveal a similar layered configuration in which layers of edge-on lying CBP cores alternate with siloxane. The difference between all CBP organizations essentially lay on the regularity of the molecular packing that modulates the interactions of neighboring conjugated cores. As a result, the materials show quite different thin film absorption and emission properties, which could be correlated to the features of the chemical architectures and the molecular organizations.

Donor–acceptor (D–A) small molecules are regarded as promising hole-transporting materials for perovskite solar cells (PSCs) due to their tunable optoelectronic properties. This paper reports the design, synthesis and characterization of three novel isomeric D-π-A small molecules PY1, PY2 and PY3. The chemical structures of the molecules consist of a pyrazolo[1,5-a]pyrimidine acceptor core functionalized with one 3,6-bis(4,4′-dimethoxydiphenylamino)carbazole (3,6-CzDMPA) donor moiety via a phenyl π-spacer at the 3, 5 and 7 positions, respectively. The isolated compounds possess suitable energy levels, sufficient thermal stability (T_d > 400 °C), molecular glass behavior with T_g values in the range of 127–136 °C slightly higher than that of the reference material Spiro-OMeTAD (126 °C) and acceptable hydrophobicity. Undoped PY1 demonstrates the highest hole mobility (3 × 10⁻⁶ cm² V⁻¹ s⁻¹) compared to PY2 and PY3 (1.3 × 10⁻⁶ cm² V⁻¹ s⁻¹). The whole isomers were incorporated as doped HTMs in planar n-i-p PSCs based on double cation perovskite FA_0.85Cs_0.15Pb(I_0.85Br_0.15)₃. The non-optimized device fabricated using PY1 exhibited a power conversion efficiency (PCE) of 12.41%, similar to that obtained using the reference, Spiro-OMeTAD, which demonstrated a maximum PCE of 12.58% under the same conditions. The PY2 and PY3 materials demonstrated slightly lower performance in device configuration, with relatively moderate PCEs of 10.21% and 10.82%, respectively, and slight hysteresis behavior (−0.01 and 0.02). The preliminary stability testing of PSCs is also described. The PY1-based device exhibited better stability than the device using Spiro-OMeTAD, which could be related to its slightly superior hydrophobic character preventing water diffusion into the perovskite layer.

In organic microcavities, a macroscopic condensate of exciton‐polaritons can be formed at high‐exciton polariton densities. The threshold for forming this condensate is proportional to the relaxation rate from initially excited excitons to these polaritons and the lifetime of the lowest energy polariton states. Although the influence of the lower polariton (LP) lifetime on the threshold has been studied, the relationship between the polariton relaxation rate and the threshold has not been fully explored. In this study, a room‐temperature polariton condensate is demonstrated at a threshold pump fluence of 9.7 ± 0.1 µJ cm⁻², in a microcavity containing 4,4″‐bis((E)‐4‐(3,6‐bis(2‐ethylhexyl)‐(9H‐carbazol‐9‐yl))styryl)‐1,1″‐biphenyl (BSBCz‐EH). By using a semiclassical model to describe the polariton kinetics, it is revealed that this low threshold results from the rapid relaxation rate from the dark exciton reservoir to the set of the LP states forming the condensate, with an effective rate W_ep ≈ 2.0 × 10⁻⁵ cm³ s⁻¹. These results show that accelerating polariton relaxation is possible and is an important factor for realizing low‐threshold polariton condensates.

Exciton‐polaritons, in which the electronic state of an excited organic molecule and a photonic state are strongly coupled, can form a Bose–Einstein condensate (BEC) at room temperature. However, so far, the reported thresholds of organic polariton BECs under optical excitation are as high asP_th = 11–500 μJ cm^–2. One route toward lowering the condensation threshold is to increase the Rabi energy by aligning the molecular transition dipole moments. In this report, it is demonstrated that control of the orientation of a perylene‐based discotic dye, which is able to self‐organize in mesogenic columnar structures, can significantly enhance exciton–photon interaction and polariton relaxation rate in optical cavities. These results show the importance of the molecular orientation for strong light–matter interactions and provide a promising strategy toward the realization of an organic low threshold polariton BEC system and electrically driven organic polariton BEC.

The synthesis of the first mesogenic donor‐acceptor polyoxometalate (POM)‐based hybrid is herein described. The structural and electronic properties of the hybrid compound were evaluated through combination of small‐ and wide‐angle X‐ray scattering, optical microscopy, electrochemistry and photoluminescence. In the solid state, the compound behaves as a birefringent solid, displaying a lamellar organization in which double‐layers of POMs and bis(thiophene)thienothiophene organic donors alternate regularly. Noticeably, the sub‐unit organizations in the composite are similar to that observed for the individual POM and organic donor precursors. Photophysical studies show that in the hybrid, the fluorescence of the organic donor unit is considerably quenched both in solution and in the solid state, which is attributed to occurrence of intramolecular charge‐separated state.