pH Effect on Two-Photon Cross Section of Highly Fluorescent Dyes Using Femtosecond Two-Photon Induced Fluorescence

• Published in: Journal of fluorescence Vol. 27; no. 1; pp. 339 - 356
• Main Authors: Makhal, Krishnandu, Goswami, Debabrata
• Format: Journal Article
• Language: English
• Published: New York Springer US 2017; Springer Nature B.V
• Subjects: Absorption cross sections; Analytical Chemistry; Binary mixtures; Biochemistry; Biological and Medical Physics; Biomedical and Life Sciences; Biomedicine; Biophysics; Biotechnology; Original Article; Protonation; Rhodamine; Two Photon Absorption (TPA); Two Photon absorption cross section (TPACS); pH and pK; Fluorescence Quantum Yield; Acid Base Equilibrium; Two Photon Induced Fluorescence (TPIF) Technique; pH and pKa
• ISSN: 1053-0509; 1573-4994
• DOI: 10.1007/s10895-016-1963-4

Effect of solution pH on two-photon absorption cross-section of highly fluorescent Coumarin and Rhodamine dyes with high repetition rate femtosecond laser pulses at 780 nm is presented using two-photon induced fluorescence technique. A correspondence in the measured two-photon and single-photon cross-section values is seen when the pH changes from acidic to basic conditions (pH = 2–10) for solutions in 1:1 water-ethanol binary mixture. By plotting changes in the single-photon and two-photon fluorescence in this pH range, the excited state pK a values are found. The ground state pK a values are also affected by the protonation deprotonation equilibrium as a result of variation in pH from acidic to basic, which are characterized by changes in absorbance spectra. Most of these single-photon and two-photon induced fluorescence spectra show characteristic blue shifts. Different fluorescence quantum yields calculated at each pH reflect a change in structure corresponding to their associated properties as a result of acid base equilibrium.