1 and 2-photon fluorescence anisotropy decay in silicon alkoxide sol-gels: Interpretation in terms of self- assembled nanoparticles

C.D. Geddes, J. Karolin, D.J.S. Birch

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

We have studied the one- and two-photon induced fluorescence anisotropy decay of rhodamine 6G (R6G) during polymerization of tetramethyl orthosilicate (TMOS) approaching the sol-to-gel transition, a time denoted tg, using time-correlated single-photon counting and femtosecond Ti:sapphire laser excitation. A biexponential decay of fluorescence anisotropy is observed at all times. We propose a different interpretation to the widely accepted view, that fluorescence anisotropy reports solely on molecular viscosity in sol-gels. We think our results are consistent with the presence of both free dye and dye bound to nm-size silica particles rather than just the coexistence of different discrete viscosity domains as reported previously. A corollary of our interpretation is that the microviscosity changes very little from that of the initial bulk sol throughout the sol-gel polymerization. Nanometer-size particles are known from small angle scattering studies to be precursors to gelation in sol-gels over a wide range of conditions and our interpretation might prove to be an important step toward understanding the self-assembly mechanisms of silicon alkoxide based materials at the molecular level. According to our measurements and interpretation, for TMOS at pH 2.3 for example, primary silica particles of 0.8-nm mean radius grow by monomer-monomer or monomer-cluster addition to produce larger structures 1.1-nm mean radius after one month.
Original languageEnglish
Pages (from-to)3835-3841
Number of pages6
JournalJournal of Physical Chemistry B
Volume106
Issue number2002
DOIs
Publication statusPublished - 2002

Keywords

  • anisotropy decay
  • silicon alkoxide sol-gels
  • nanoparticles
  • nanoscience

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