TY - JOUR
T1 - Cryogenic fluorescence spectroscopy of oxazine ions isolated in vacuo
AU - Kjær, Christina
AU - Vogt, Emil
AU - Langeland, Jeppe
AU - Christensen, Nanna Falk
AU - Lindkvist, Thomas Toft
AU - Kjaergaard, Henrik G.
AU - Nielsen, Steen Brøndsted
N1 - Publisher Copyright:
© 2023 The Royal Society of Chemistry
PY - 2023/11
Y1 - 2023/11
N2 - Recent developments in fluorescence spectroscopy have made it possible to measure both absorption and dispersed fluorescence spectra of isolated molecular ions at liquid-nitrogen temperatures. Absorption is here obtained from fluorescence-excitation experiments and does not rely on ion dissociation. One large advantage of reduced temperature compared to room-temperature spectroscopy is that spectra are narrow, and they provide information on vibronic features that can better be assigned from theoretical simulations. We report on the intrinsic spectroscopic properties of oxazine dyes cooled to about 100 K. They include six cations (crystal violet, darrow red, oxazine-1, oxazine-4, oxazine-170 and nile blue) and one anion (resorufin). Experiments were done with a home-built setup (LUNA2) where ions are stored, mass-selected, cooled, and photoexcited in a cylindrical ion trap. We find that the Stokes shifts are small (14-50 cm−1), which is ascribed to rigid geometries, that is, there are only small geometrical changes between the electronic ground and excited states. However, both the absorption and the emission spectra of darrow-red cations are broader than those of the other ionic dyes, which is likely associated with a less symmetric electronic structure and more non-zero Franck-Condon factors for the vibrational progressions. In the case of resorufin, the smallest ion under study, vibrational features are assigned based on calculated spectra.
AB - Recent developments in fluorescence spectroscopy have made it possible to measure both absorption and dispersed fluorescence spectra of isolated molecular ions at liquid-nitrogen temperatures. Absorption is here obtained from fluorescence-excitation experiments and does not rely on ion dissociation. One large advantage of reduced temperature compared to room-temperature spectroscopy is that spectra are narrow, and they provide information on vibronic features that can better be assigned from theoretical simulations. We report on the intrinsic spectroscopic properties of oxazine dyes cooled to about 100 K. They include six cations (crystal violet, darrow red, oxazine-1, oxazine-4, oxazine-170 and nile blue) and one anion (resorufin). Experiments were done with a home-built setup (LUNA2) where ions are stored, mass-selected, cooled, and photoexcited in a cylindrical ion trap. We find that the Stokes shifts are small (14-50 cm−1), which is ascribed to rigid geometries, that is, there are only small geometrical changes between the electronic ground and excited states. However, both the absorption and the emission spectra of darrow-red cations are broader than those of the other ionic dyes, which is likely associated with a less symmetric electronic structure and more non-zero Franck-Condon factors for the vibrational progressions. In the case of resorufin, the smallest ion under study, vibrational features are assigned based on calculated spectra.
UR - http://www.scopus.com/inward/record.url?scp=85178590092&partnerID=8YFLogxK
U2 - 10.1039/d3cp04615j
DO - 10.1039/d3cp04615j
M3 - Journal article
C2 - 38014982
AN - SCOPUS:85178590092
SN - 1463-9076
VL - 25
SP - 32715
EP - 32722
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 47
ER -