ChemInform Abstract: Effect of γ‐Cyclodextrin on the Intramolecular Charge Transfer Processes in Aminocoumarin Laser Dyes

Abstract

044ChemInform Abstract (I) and (II) (steady-state and time-resolved studies on the emission properties).

Photophysical Properties of Coumarin 1 in Bile Salt Aggregates: An Insight into the Role of Bile Salt Structure on the Aggregation Behavior

“…In highly polar protic solvents (Δf ≥ 0.28) such as water, the nonfluorescent TICT form is stabilized over the fluorescent ICT form; as a result, the quantum yield is low in pure aqueous medium. 15,17,22,23 There is a significant enhancement in the intensity with a remarkable blue shift in the emission maximum observed in the presence of bile salts. The fluorescence characteristics of Cou1 displayed strong dependence on the concentration as well as the nature of bile salt (dihydroxy or trihydroxy).…”

“…The enhanced intensity can be attributed to the reduction in the TICT-induced nonradiative decay and stabilization of the ICT state, reflecting the hydrophobic nature of the microenvironment for Cou1. 15,17,22,23 The blue shift of the emission maximum indicates the less polar nature of the surrounding of Cou1 in the bile salts as compared to the aqueous medium. The plots of emission intensity with concentration of cholates (insets in Figure 2A−C) though follow more or less a sigmoid shape, the breakpoints, however, are not very apparent unlike in the case of deoxycholates.…”

“…Once the micellization process commences, Cou1 partitions into the less polar and hydrophobic micellar interior, resulting in the enhancement in emission intensity and blue shift in emission maximum. The enhanced intensity can be attributed to the stabilization of the ICT state and reduction in the TICT-induced nonradiative decay 15,17,22,23 on account of the confinement of Cou1 inside the hydrophobic nanocavity of deoxycholate aggregates, thus modulating the photophysics of Cou1. This is further supported by the fact that Coumarin 102 (Cou102, Scheme S1), where the amino group is structurally rigid and the rotation of the 7-amino group is hindered inhibiting the formation of a TICT state, 15 shows almost insignificant response to the micellization process of bile salts (Figure S2).…”

“…5,15−18,20−24 This conversion of ICT to TICT results in a large reduction in the quantum yield and fluorescence lifetime as the TICT state formation introduces a new nonradiative decay channel for the excited molecule. 15,17,18 The stabilization of the TICT state of Cou1 is effectively due to the combined effect of higher solvent polarity and the specific solute−solvent hydrogen bonding interaction. 15,16,18,19 Therefore, the photophysics of Cou1 is extremely sensitive to its local environment in terms of the polarity, hydrogen bonding ability, pH, and microviscosity or rotational hindrance of the surrounding medium.…”

“…5,12−15 This sensitivity has led to its widespread application as a sensitive fluorescent probe for a wide range of systems, including homogeneous solvents and mixtures and micro-heterogeneous materials. The effect of diverse supramolecular systems such as cyclodextrins, 17 proteins, 18,20,21 cucurbit[n]urils, 22,23 aerosol OT (AOT) reverse micelles, 24 polymers, 25 etc. on the photophysical properties of Cou1 has been explored, and important information about the physical and structural aspects of these organized systems has been obtained.…”