# Protein–Chromophore Biohybrids for Tunable Delayed Emission **Adhil Kabeer**^a, **Juan Cabanillas**^a, and **Sara Hernández**^a,* ^a IMDEA Nanoscience, Madrid, Spain **Presenting Author:** adhil.kabeer@imdea.org --- Proteins possess three-dimensional structures that confer upon them a cardinal role in a plethora of natural processes, *viz.* photosynthesis. Biohybrids are novel systems that harness the synergy between *de novo* proteins and chromophores for next-generation applications in light-emitting devices.¹ Yet, precise control over how the protein environment influences chromophore relaxation remains elusive in these systems. We use Thermally Activated Delayed Fluorescence Chromophores (TADF-Cs), known for their high quantum efficiency and widespread use in OLEDs. However, non-radiative energy transfer to the host materials remains a major bottleneck, limiting their versatility and large-scale applications.² We advocate a novel approach to augment TADF properties through a conformationally rigid, chiral *de novo* protein environment³ (Figure 1). Within the protein cavity, the chromophore is confined, enabling nuanced control over its photophysical properties. Herein, we employ **Eosin Y (Ey)** as a model molecule. Owing to its relatively small size, Ey can fit within the protein cavity.^4,5 Based on this model, we investigate the possibility of fine-tuning the singlet–triplet energy gap through the protein environment. We rely on a Michael addition reaction to label the protein with Ey molecules within the cavity. Our results indicate the successful expression of proteins containing the desired mutations, along with efficient labeling by Ey. Temperature-dependent studies reveal that the motion of Ey couples with the dynamics of the protein, thereby enhancing the phosphorescence decay rate. Taken together, this work provides molecular-level insights into how the protein environment influences the photophysics of these chromophores and lays the foundation for the development of next-generation protein-based photonic materials. --- ## References 1. M. Marques dos Santos *et al.* **Chem. Rev.** **2024**, *124*, 13736–14110. 2. H. Yersin; T. Monkowius. **Adv. Photonics Res.** **2024**, 2400111, 1–44. 3. C. Karas; M. Hecht. **Life** **2020**, *10*, 1–15. 4. G. Serrano; C. Echavarría; S. Mejias. **Protein Sci.** **2024**, *33*, e5164. 5. M. Arbeloa; V. Porcal; G. Bertolotti; M. Previtali. **J. Photochem. Photobiol., A** **2013**, *252*, 31–36. --- **Figure 1.** Schematic illustration of the *de novo* protein cavity encapsulating a chromophore, enabling modulation of its photophysical properties and tunable delayed emission.

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