Neradijativni relaksacijski mehanizmi elektronski pobuđenog fenilalanina u modelnim peptidima

A systematic study of the non-radiative deactivation mechanisms of the three photoexcited N-acetylphenylalanylamide conformers was conducted in order to disclose the experimentally observed conformational dependent lifetime of phenyl vibrationless 1* excited state. The all-atom trajectory surface hopping non-adiabatic molecular dynamics simulations, based on linear response time dependent density functional theory, were utilized for blind screening of relaxation pathways and revealed a number of excitation transfer mechanisms from 1* to the 1n* excited states localized on each of the two amide groups. Possible pathways were further refined by obtaining conical intersection barrier energies from corresponding reaction paths constructed at the coupled cluster (CC2) level of theory. Finally, from semiclassical consideration of conical intersection accessibility with only the nuclear zero point vibrational energy and from the increased rigidity of the second amide group towards distorsion upon its methylation, it was concluded that the classically accessible part of conical intersection seam for population transfer to the 1n* state of the second amide group is the largest for the conformer with the shortest 1* state lifetime.Provedeno je sustavno istraživanje neradijativnih deaktivacijskih mehanizama odgovornih za eksperimentalno opaženu konformacijsku ovisnost vremena života vibracijski osnovnog pobuđenog fenilnog 1* elektronskog stanja u tri konformera N-acetilfenilalanilamida. Simulacije metodom neadijabatske molekulske dinamike, s preskokom među plohama elektronske potencijalne energije dobivenih vremenski ovisnom teorijom funkcionala gustoće, ukazale su na nekoliko mehanizama prijenosa ekscitacije iz 1* u 1n* stanja locirana na pojedinim amidnim grupama. Pronađeni mehanizmi potom su utočnjeni pripadajućim vrijednostima energijama barijera koničnih presjecišta dobivenih ih reakcijskih puteva izračunatim na razini teorije spregnutih grozdova (CC2). Konačno, iz poluklasičnog razmatranja dostupnosti koničnog presjecišta samo na temelju nuklearne vibracijske energije nulte točke te iz povećanja rigidnosti druge peptidne skupine naspram njene deformacije usljed metilacije, određeno je kako klasično dostupan dio šava koničnog presjecišta za prijenos populacije u 1n* stanje druge peptidne skupine je najveći u konformeru s najkraćim vremenom života pobuđenog 1* stanja

Non-radiative relaxation mechanisms of electronically excited phenylalanine in model peptides

A systematic study of the non-radiative deactivation mechanisms of the three photoexcited N-acetylphenylalanylamide conformers was conducted in order to disclose the experimentally observed conformational dependent lifetime of phenyl vibrationless 1ππ* excited state. The all-atom trajectory surface hopping non-adiabatic molecular dynamics simulations, based on linear response time dependent density functional theory, were utilized for blind screening of relaxation pathways and revealed a number of excitation transfer mechanisms from 1ππ* to the 1nπ* excited states localized on each of the two amide groups. Possible pathways were further refined by obtaining conical intersection barrier energies from corresponding reaction paths constructed at the coupled cluster (CC2) level of theory. Finally, from semiclassical consideration of conical intersection accessibility with only the nuclear zero point vibrational energy and from the increased rigidity of the second amide group towards distorsion upon its methylation, it was concluded that the classically accessible part of conical intersection seam for population transfer to the 1nπ* state of the second amide group is the largest for the conformer with the shortest 1ππ* state lifetime