Photoswitchable Organic Nanoparticles and a Polymer Film Employing Multifunctional Molecules with Enhanced Fluorescence Emission and Bistable Photochromism
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Preparation of FPONs: All suspensions of FPONs were prepared by the reprecipitation method from THF solution with distilled water. Volume fractions of THF and water were adjusted to 20 and 80 % respectively. See ref. [19] for details.
Fluorescence quantum yields: The fluorescence quantum yields (ΦF) were relatively calculated using 9 10‐diphenylanthracene (DPA) in benzene (see ref. [22]) and in PMMA (see refs. [29 30]) as a standard reference (1×10−3 m ΦF=83 %). Through this method theΦFvalues of FPONs of1 awere determined as 3.2 5.1 4.1 and 3.4 % (${\lambda {{{\rm FPONs}\hfill \atop {\rm max}\ {\rm em}\hfill}}}$=485 489 491 and 493 nm ${\lambda {{{\rm FPONs}\hfill \atop {\rm max}\ {\rm abs}\hfill}}}$=371 374 378 and 382 nm) in the1 aform and as 0.20 0.09 0.04 and 0.02 % in the PSS with increasing FPON size of 40±10 125±25 200±50 and 275±75 nm respectively. It is reasonably considered that the slight reduction of theΦFvalues in 200±50 and 275±75 nm FPONs of1 aresults from the highly increased virtual absorbance values by increased light scattering. In fact the extent of the apparent absorbance of the FPONs of1 aat the excitation wavelength that is at 360 nm was almost linearly proportional to their suspension concentrations in spite of the inverse proportional relationship between the mean radius and the surface‐to‐volume ratio of the FPONs.
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Ruban A. V., 1993, J. Photochem. Photobiol. B, 21
Determination of the conformational population and conversion rate: A1H NMR spectroscopic study (2×10−4 mof CDCl3solution 22 °C 300 MHz) on the1 aform showed that the parallel and antiparallel conformations were equally populated in solution as evident by there only being two singlet resonances atδ=1.98 and 1.91 ppm without any splitting. These signals were assigned as the methyl protons at the 2‐positions of the thiophene rings of the1 aform (see ref. [27]). The conversion rate of about 35 % in the PSS was calculated by the integrated ratio between the singlet peaks of methyl protons in the1 aform and those in the1 bform which newly appeared atδ=2.15 and 2.11 ppm.
Guilbault G. G., 1990, Practical Fluorescence