Theoretical insights into the π→π∗ transition and the large Stokes shift of a curcumin-based chromophore Catharina B. de Araújo, Lennon Rodrigues Oliveira, Danillo Valverde, Rodrigo Gester, Kaline Coutinho, et al. Theoretical Chemistry Accounts, 2026 This theoretical study investigates the photophysical properties and excited-state dynamics of the monocarbonyl curcumin derivative (1E,4E)-1,5-bis(4-dimethylaminophenyl)penta-1,4-dien-3-one (CCM) in aprotic solvents. Using DFT/TD-DFT with the CAM-B3LYP functional and PCM solvation modeling, we analyze the solvent-dependent absorption spectra, $$\\pi \\rightarrow \\pi ^*$$ π → π ∗ transition, and the large Stokes shifts observed experimentally. The $$S_0 \\rightarrow S_1$$ S 0 → S 1 transition demonstrates a mixed contribution from locally excited (LE) and intramolecular charge transfer (CT) characters, showing minimal sensitivity to solvent polarity. The CT component accounts for 68–69% of the electronic reorganization, with charge transfer from the N,N-dimethylaniline (donor) units to the divinyl ketone (acceptor) core, as indicated by natural transition orbitals (NTOs) and Hirshfeld population analysis. XMS-CASPT2 multiconfigurational calculations corroborate the TD-DFT picture, revealing a bright $$^1(\\pi \\pi ^*)$$ 1 ( π π ∗ ) state containing a mixture of LE and CT character. Gas-phase excited-state optimizations show that the lowest excited state is an $$^1(n\\pi ^*)$$ 1 ( n π ∗ ) dark state with negligible oscillator strength, while the bright $$^1(\\pi \\pi ^*)$$ 1 ( π π ∗ ) state lies slightly above it; consequently, fluorescence originates from the relaxed $$^1(\\pi \\pi ^*)$$ 1 ( π π ∗ ) minimum. Large Stokes shift (3607 to 5773 cm $$^{-1}$$ - 1 ) has been linearly correlated with solvent polarity by Lippert-Mataga plot (R = 0.985), driven by dipole moment changes ( $$\\Delta \\mu \\sim 3.1-3.6$$ Δ μ ∼ 3.1 - 3.6 Debye) upon excitation. Calculations reproduce experimental absorption and emission trends, that is, the redshift in polar solvents, and validate CAM-B3LYP for curcumin derivatives. This work elucidates the mixed ICT-LE character in various solvents and provides design insights for fluorophores in sensing and optoelectronics.
Lanthanide-doped nanocrystals enable organic room-temperature phosphorescence in solution through direct triplet excitation Huangtianzhi Zhu, Rakesh Arul, Zhao Jiang, Bofeng Xue, Matteo Fornasarig, et al. Nature Chemistry, 2026 Organic triplet excitons are of great interest for applications in optoelectronics, photochemistry and theranostics. Due to spin-selection rules, triplets are ‘dark states’, rendering direct photoexcitation from the ground state and efficient phosphorescent emission nearly impossible. Overcoming these spin-dependent limitations is a long-standing challenge. Here we report a universal method to brighten organic triplet excitons by attaching chromophores onto the surface of lanthanide-doped nanocrystals, enabling spin-exchange coupling between the unpaired spins of lanthanide ions and organic molecules. This allows direct photoexcitation of the organic triplets, and room-temperature, nanosecond-timescale, oxygen-insensitive phosphorescence in both solution and film under ambient conditions. Different organic chromophores and lanthanide ions are combined to obtain phosphorescence in the visible and near-infrared range. Compared with common organic phosphorescence, which only exists in crystals or at low temperature, the triplet emission established here does not require crystallization, low temperatures or an inert atmosphere. Our approach could open avenues to the application of room-temperature organic phosphorescence in optoelectronic devices and biological labelling and imaging.
Multiscale modeling of structural disorder and environmental effects on the ground and excited states properties of a conjugated donor-acceptor polymer in the bulk phase Leandro R Franco, Danillo Valverde, Cleber Marchiori, Ellen Moons, Ergang Wang, et al. Jphys Energy, 2025 We herein undertook a multiscale approach combining molecular dynamics (MD) simulations of solution-processed polymer bulk with sequential quantum mechanics/molecular mechanics (s-QM/MM) calculations to assess the influence of structural disorder and environmental effects on the electronic structure of conjugated donor–acceptor (D–A) polymers in bulk phase. As a case study, PF5-Y5 polymer bulk formation is modeled via gradual solvent removal under ambient conditions. The electronic structure is analyzed using state-of-the-art electronic structure methods, including optimally tuned range-separated hybrids (OT-DFT), double-hybrid functionals, and the second order algebraic diagrammatic construction (ADC(2)) method as a reference. Environmental effects are accounted for using both implicit and explicit electrostatic embedding models. Our findings reveal that structural disorder at the D–A interfaces reduces frontier orbital overlap and narrows the fundamental gap by localizing the orbitals, primarily due to significant LUMO stabilization on the acceptor unit. This effect enhances the charge-transfer (CT) character of low-lying singlet and triplet states within the OT-DFT approach, while double hybrid methods preserve a more localized nature. Disorder reshapes the energetic gaps between singlet-singlet and singlet-triplet excited states and increases its energetic disorder, with CT-rich states being particularly sensitive. Explicit electrostatic embedding further amplifies CT character and disorder in singlets while preserving triplet localization. These effects contribute to spectral broadening and help explain a shoulder feature in the visible region, linking it to structural disorder and ambient anisotropy alongside CT excitations. The choice of QM method and environment treatment in QM/MM simulations is critical, neglecting anisotropy in the surroundings can influence the excited-state descriptions in D–A materials. This work advances our theoretical understanding of organic photovoltaics by highlighting these interrelated effects.
Curcuminoid Derivatives with a Donor-Acceptor-Donor Architecture: an Outstanding Platform for Highly-Efficient Near-Infrared Electroluminescence and Amplified Spontaneous Emission Anthony D'Aléo, Xun Tang, Dae‐Hyeon Kim, Danillo Valverde, Elena Zaborova, et al. Advanced Optical Materials, 2025 The development of high‐efficiency near‐infrared (NIR) emitters for organic light‐emitting diodes (OLEDs) and organic semiconductor lasers has become an important target in organic photonics. Herein, it is demonstrated that donor‐acceptor‐donor borondifluoride curcuminoid derivatives represent a versatile and simple platform for the molecular engineering of high‐efficiency NIR emitters combining thermally‐activated delayed fluorescence (TADF) with excellent electroluminescence properties and amplified spontaneous emission (ASE) activity. A series of donor‐acceptor‐donor curcuminoid compounds containing triphenylamino‐substituents for the donor side groups and various acceptor units in the meso position were designed and synthesized. The investigation of the effects of the molecular structure on the TADF properties show that the nature of the substituents enables a fine tuning of the emission wavelengths while maintaining high photoluminescence quantum yield values. These NIR TADF dyes were used in OLEDs with an external quantum efficiency of almost 1% for a maximum emission wavelength of 797 nm. They also show a low threshold tuneable amplified spontaneous emission between 725 and 900 nm. Overall, this study provides new essential insights to rationalize the TADF activity of this family of NIR emitters and offers important prospects for designing the next generation of NIR TADF‐OLEDs and organic semiconductor laser materials.
Excited state relaxation mechanisms and tautomerism effects in 2,6-Diamino-8-Azapurine Leonardo M. F. Oliveira, Danillo Valverde, Gustavo Juliani Costa, Antonio Carlos Borin Photochemistry and Photobiology, 2025 The photochemistry of 9H‐2,6‐diamino‐8‐azapurine (9H‐8AZADAP), a promising fluorescent probe, was investigated using the Multi‐State Complete‐Active‐Space Second‐Order Perturbation Theory (MS‐CASPT2) quantum chemical method, along with the Average Solvent Electrostatic Configuration and Free Energy Gradient (ASEC‐FEG) and Polarizable Continuum Model (PCM) to take into account water solvation effects. For both isolated and solvated species, the main photochemical event is initiated by the absorption of light from ground‐state to the bright 1(ππ* La) state, which undergoes barrierless evolution to its minimum energy region (1(ππ* La)min) without crossing any other potential energy surface (PES). Subsequently, the excess of energy is released through fluorescence. From the 1(ππ* La)min region, two radiationless decay pathways back to the initial ground state, mediated by two distinct conical intersections between the ground and 1(ππ* La) states, are found to be unlikely due to the presence of high energy barriers in both environments. Our results also indicate that the solvation effects are more pronounced when using the ASEC‐FEG method, which predicts larger structural and energy changes, especially concerning energetic barriers. Based on the free energy perturbation theory (FEP), a hypothetical thermodynamic cycle was devised, from which we infer that in an aqueous environment the N3 site is the most favorable for protonation. We also conclude that the 8H‐8AZADAP tautomer is responsible for the fluorescent band observed experimentally at 410 nm and elucidates the mechanism of phototautomerism.
Red-to-Near-Infrared Electroluminescence and Low-Threshold Amplified Spontaneous Emission from Solution-Processable Fluorescent Diketopyrrolopyrrole Derivatives Anthony D’ Aléo, Virginie Placide, Hao Ye, Matteo Fornasarig, Danillo Valverde, et al. Chemphotochem, 2025 A detailed investigation of the photophysical, electroluminescence, and amplified spontaneous emission (ASE) properties of two solution‐processable fluorescent diketopyrrolopyrrole derivatives is reported. Photophysical measurements are carried out in solution and blend films containing a 4,4′‐bis(N‐carbazolyl)‐1,10‐biphenyl (CBP) or a poly[(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,8‐diyl)] host, to gain important insights into the excited state behavior of these dyes. Quantum chemical calculations are also carried out to support the experimental findings. An optimization of the doping concentration in the CBP blends is necessary to reduce the strong aggregation. This optimization led for both near‐infrared‐emitting dyes to a substantial increase of the photoluminescence quantum yield, which can reach values as high as 60%. It is also found that the blend films show excellent ASE properties with a threshold as low as 3.5–4.5 μJ cm−2 for peak wavelengths of 739 and 727 nm. In addition, the electroluminescence properties of the two organic laser dyes are examined in organic light‐emitting diodes (OLEDs). The best OLED device shows a maximum external quantum efficiency value of around 2%. Overall, this study demonstrates the excellent potential of diketopyrrolopyrrole derivatives for high‐performance near‐infrared organic semiconductor lasers and provides useful information for the design of new efficient near‐infrared emitters for optoelectronic applications.
Can ΔSCF and ROKS DFT-Based Methods Predict the Inversion of the Singlet-Triplet Gap in Organic Molecules? Danillo Valverde, Gaetano Ricci, Juan Carlos Sancho-García, David Beljonne, Yoann Olivier Journal of Chemical Theory and Computation, 2025 Inverted singlet-triplet gap systems (INVEST) have emerged as an intriguing class of materials with potential applications as emitters in Organic Light Emitting Diodes (OLEDs). Indeed, this type of material exhibits a negative singlet-triplet energy gap (ΔEST), i.e., an inversion of the lowest singlet (S1) and triplet (T1) excited states, that goes against Hund's rule. In this study, the ΔEST of a set of 15 INVEST molecules has been computed within the framework of Restricted Open-Shell Kohn-Sham (ROKS) and Delta Self-Consistent Field (ΔSCF) methods and the results were benchmarked against wavefunction-based calculations performed at the EOM-CCSD, NEVPT2, and SCS-CC2 levels. We find that ROKS always (and wrongly) predicts a positive ΔEST with global hybrid, meta-GGA, and long-range corrected functionals and that this is almost functional-independent. We also show that the only way to obtain an inverted gap was to resort to double hybrid functionals. In contrast, using the above-mentioned functionals, ΔSCF usually gives a negative ΔEST, although the results are largely functional-dependent. Overall, applying a ΔSCF method based on the PBE0 functional provides the lowest MSD and MAD with respect to the EOM-CCSD results. We further show that the singlet-triplet inversion is driven by different degrees of orbital relaxation in the singlet versus triplet state and that this is well captured by ΔSCF calculations. As a matter of fact, this orbital relaxation in ΔSCF somehow mimics the involvement of double and higher-order excitations in EOM-CCSD, which leads to a difference in spatial localization of the α and β spins, and thus introduces (local) spin polarization effects sourcing the negative ΔEST. However, care should be taken when using the ΔSCF method to screen materials with potential INVEST behavior in view of their limited quantitative correlation with reference EOM-CCSD results on the molecular data basis used here.
Analysis of the NMR Parameters Shielding and Spin-Spin Coupling Constants of Glycine Conformers Danillo Valverde, H. C. Georg, G. I. Pagola, P. Provasi Journal of Physical Chemistry A, 2025 In this study, we worked at the CCSD/aug-cc-pVTZ level to obtain the conformers of glycine in its neutral and zwitterionic forms in the gas and water phases. We then computed the NMR properties (spin-spin coupling constants and nuclear magnetic shieldings) at the SOPPA/aug-cc-pVTZ-J level. We attempt to elucidate the apparent discrepancy arising from two previous works by Valverde et al. [J. Chem. Phys., 2018, 148, 024305] and Caputo and Provasi [Sci, 2021, 3, 41]. Our optimized structures align with previous theoretical predictions, although some geometries were not found. Additionally, our results suggest that in the gas phase the Δ 1J(O,C) = 1J(Ocis,CO) - 1J(Otrans,CO) is positive when the acid group is in the trans conformation and negative in the cis conformation; however, this trend is not well reproduced in water. From magnetic shielding calculations, we cannot distinguish between an O-H in the cis or trans conformation.
