Acknowledgements: G.D.M. and J.A.S. gratefully acknowledges CONICET doctoral fellowship. G.D.M. also acknowledges to CINECA supercomputing (project NAFAA - HP10B4ZBB2). UNM acknowledges CINECA supercomputing center (projects V-COINS - HP10C35IQ1 and V-CoIns - HP10BY0AET), and Elettra-TeraFERMI project 20224056. AH and G.D.M would like to acknowledge the European Commission for funding on the ERC Grant HyBOP 101043272. DAE, MCGL, JAS and UNM would like to acknowledge founding from PICT 2020 01828 UNM, MCGL, DAE, Agencia I-+d+i. IR gratefully acknowledges the use of HPC resources of the “Pôle Scientifique de Modélisation Numérique- (PSMN) of the ENS-Lyon, France. J.V’s work has partially received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skodowska Curie grant agreement No. 101025385. We also acknowledge Prof. Sir John Walker, Prof. David Palmer, Dr. Johannes Schmidt, Dr. Zeinab Ebrahimpour, Dr. Pablo Videla, Prof. Victor S. Batista and Dr. Marcello Coreno for useful discussions.AbstractChallenging the basis of our chemical intuition, recent experimental evidence reveals the presence of a new type of intrinsic fluorescence in biomolecules that exists even in the absence of aromatic or electronically conjugated chemical compounds. The origin of this phenomenon has remained elusive so far. In the present study, we identify a mechanism underlying this new type of fluorescence in different biological aggregates. By employing non-adiabatic ab initio molecular dynamics simulations combined with a data-driven approach, we characterize the typical ultrafast non-radiative relaxation pathways active in non-fluorescent peptides. We show that the key vibrational mode for the non-radiative decay towards the ground state is the carbonyl elongation. Non-aromatic fluorescence appears to emerge from blocking this mode with strong local interactions such as hydrogen bonds. While we cannot rule out the existence of alternative non-aromatic fluorescence mechanisms in other systems, we demonstrate that this carbonyl-lock mechanism for trapping the excited state leads to the fluorescence yield increase observed experimentally, and set the stage for design principles to realize novel non-invasive biocompatible probes with applications in bioimaging, sensing, and biophotonics.</jats:p
