Ultrafast Excited-State Dynamics of Eosin B: A Potential Probe of the Hydrogen-Bonding Properties of the Environment

Abstract

The photophysics of two dyes from the xanthene family, eosin B (EB), and eosin Y (EY) has been investigated in various solvents by femtosecond transient absorption spectroscopy, first, to clarify the huge disparity of the EB fluorescence lifetimes reported in literature, and, second, to understand the mechanism responsible for the ultrafast excited-state deactivation of EB in water. The excited-state lifetime of EB was found to be much shorter in water and in other protic solvents, due to the occurrence of hydrogen-bond assisted nonradiative deactivation. This mechanism is associated with the hydrogen bonds between the solvent molecules and the nitro groups of EB, which become stronger upon optical excitation due to the charge-transfer character of the excited-state. This process is not operative with EY, where the nitro groups are replaced by bromine atoms. Therefore, the excited-state lifetime of EB in solution is directly related to the strength of the solvent as a hydrogen-bond donor, offering the possibility to build a corresponding scale based on the fluorescence quantum yield or lifetime of EB. This scale of hydrogen-bonding strength could be especially useful for studies of liquid interfaces by time-resolved surface second harmonic generation

Hydrogen-Bond-Assisted Excited-State Deactivation at Liquid/Water Interfaces

“…As a consequence, the S 1 lifetime of EB decreases significantly with an increasing hydrogen-bonding ability of the solvent. 27 Therefore, the slow excitedstate dynamics measured by TRSSHG leads us to conclude that EB is much less hydrogen-bonded with interfacial water than with bulk water. This interpretation agrees well with a previous study of EB at air/water interfaces, 18 where the reorientational dynamics of EB was compared to that of rhodamine 6G (R6G).…”

“…27 Consequently, the excited-state lifetime of this dye is directly related to its hydrogen-bonding properties with surrounding solvent molecules.…”

“…In EB, on the other hand, the absorption spectrum remains unchanged, regardless of the solvent, and, additionally, the triplet state is not populated, making this dye most convenient for TRSSHG studies. 27 Using TRSSHG, we have monitored the decay of optically excited EB molecules at dodecane/water and decanol/water interfaces and interpreted the results in terms of the ability of interfacial water to form hydrogen bonds with EB. However, we have first studied the influence of interfacial aggregation of EB on its excited-state dynamics, to separate this effect from that of hydrogen bonding with water.…”

In2O3 cubes: synthesis, characterization and photocatalytic properties

“…39 We assessed the potential validity of cube In 2 O 3 for photocatalytic removal of EB. As a comparison, the EB photodegraded by commercial In 2 O 3 was also performed.…”

Photoinduced Electron Transfer Reactions: From the Elucidation of Old Problems in Bulk Solutions Towards the Exploration of Interfaces

“…For example, the excitedstate lifetime of Eosin B has been found to strongly depend on its ability to form hydrogen bonds with surrounding solvent molecules. [45] We have used this property to probe hydrogen bonding at liquid-liquid interfaces. [46] Measurements at liquid-liquid interfaces can also be used to obtain mechanistic information on the deactivation pathway of an excited molecule.…”