Abstract
The spontaneous self-assembly of supramolecular structures within biological environments offers a powerful strategy for developing functional biomaterials capable of interacting with living systems. By integrating optical spectroscopy with quantum-chemical calculations, it is demonstrated that the assembly of 2,6-diphenyl-3,5-dimethyl-dithieno[3,2-b:2',3'-d]thiophene-4,4-dioxide (DTTO) molecules into fibers within cells leads to distinct photophysical properties and enhanced biocompatibility. Photoluminescence and transient absorption spectroscopy reveal weak intermolecular interactions in the fibers, which are sufficient for supporting energy and charge transport. Additionally, the observation of stimulated emission suggests that optical gain can be achieved within these fibers. Biological assays on Escherichia coli exposed to DTTO provide insight into the material's stability and biocompatibility. While DTTO aggregates formed in aqueous environments exhibit phototoxicity, DTTO fibers produced by cells do not. Time-resolved spectroscopy suggests that this difference arises from the absence of long-lived photoexcited states in the fibers, a consequence of their distinct molecular packing. These findings underscore the fundamental role of cell-guided self-assembly in tuning optical properties and, consequently, in modulating biological interactions, positioning DTTO fibers as promising candidates for biocompatible electronic interfaces and intracellular applications.