TY  - JOUR
A1  - Kaiser, Christoph
A1  - Halbritter, Thomas
A1  - Heckel, Alexander
A1  - Wachtveitl, Josef
T1  - Proton-transfer dynamics of photoacidic merocyanines in aqueous solution
T2  - Chemistry
N2  - Photoacids attract increasing scientific attention, as they are valuable tools to spatiotemporally control proton-release reactions and pH values of solutions. We present the first time-resolved spectroscopic study of the excited state and proton-release dynamics of prominent merocyanine representatives. Femtosecond transient absorption measurements of a pyridine merocyanine with two distinct protonation sites revealed dissimilar proton-release mechanisms: one site acts as a photoacid generator as its pKa value is modulated in the ground state after photoisomerization, while the other functions as an excited state photoacid which releases its proton within 1.1 ps. With a pKa drop of 8.7 units to −5.5 upon excitation, the latter phenolic site is regarded a super-photoacid. The 6-nitro derivative exhibits only a phenolic site with similar, yet slightly less photoacidic characteristics and both compounds transfer their proton to methanol and ethanol. In contrast, for the related 6,8-dinitro compound an intramolecular proton transfer to the ortho-nitro group is suggested that is involved in a rapid relaxation into the ground state.
KW  - cyanines
KW  - photoacid
KW  - proton transfer
KW  - spiro compounds
KW  - ultrafast spectroscopy
Y1  - 2021
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/63890
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-638904
SN  - 1521-3765
N1  - We thank the Deutsche Forschungsgemeinschaft (DFG) for funding through, SFB 902 „Molecular Principles of RNA-based Regulation“, GRK 1986 “CLiC – Complex Light Control” and grant number WA 1850/4-2. Open access funding enabled and organized by Projekt DEAL.
VL  - 27
IS  - 35
SP  - 9160
EP  - 9173
PB  - Wiley-VCH
CY  - Weinheim
ER  -