Structural and Optical Properties of Rhodamine Dye Aqueous Solutions and Thin Films
Mara Dubnicka, William B. Euler, J. Phys. Chem. C, 2022, 126, 19386 – 19396
Abstract
The absorption and emission spectra of six rhodamine dyes are examined in dilute aqueous solution and as thin films on a glass substrate. The absorption and emission spectra in water can be described using the displaced harmonic oscillator (DHO) model. The changes of the absorption maxima in aqueous solution are controlled by the substitution of alkyl groups on the xanthene nitrogen atoms, which is supported by density functional theory calculations. In addition, the nature of the alkyl substitution influences the excited state lifetimes. In contrast, the photophysical behavior of thin films of the dyes cannot be described using the DHO model. Rather, the spectral changes depend on interactions with the glass substrate for thin films and by aggregation for thicker films. The intensity of the emission spectra can be maximized by controlling the film thickness to be less than a monolayer.
