Supporting information:
Synthesis and characterization of Na(Y,Gd)F4 upconversion nanoparticles and
an investigation of their effects on the photophysical properties of an
unsubstituted tetrathiophenoxy phthalocyanine
Jessica M. Taylor,1 Christian Litwinski,1,2 Tebello Nyokong,1 Edith M. Antunes1,3*
1Department
2PicoQuant
of Chemistry, Rhodes University, Grahamstown, 6140, South Africa.
GmbH, Rudower Chaussee 29, 12489 Berlin, Germany.
3Department
of Chemistry, University of the Western Cape, Bellville, 7535, South Africa.
*Corresponding author: ebeukes@uwc.ac.za; +27(21)9594020.
Fig. 1. Hexagonal crystal showing a and c axes. The highlighted area represents the 0001 plane.
Scheme 1: Synthesis of tetrathiophenoxy H2Pc from a thiophenoxy phthalonitrile precursor.
Equipment
Transmission electron microscope (TEM) images were obtained using a Zeiss Libra TEM at 120 kV
accelerating voltage. Energy dispersion x-ray spectroscopy (EDX) was performed utilizing a TESCAN
Vega TS 5136LM scanning electron microscope equipped with an INCA PENTA FET (EDX) from
Oxford Instruments. X-ray diffraction was undertaken using a Bruker D8 discover equipped with a
LynxEye detector and Cu-Kα radiation source (1.5403 Å, nickel filter). Samples were analysed upon a
silicon wafer slide and diffraction data were collected at 2θ values between 10o – 100o using a locked
coupled scan with 9381 steps of 0.00959o at a rate of 0.4 s per step and a slit width of 6 mm. Data were
analysed using evaluation curve fitting software, EVA (Bruker), and Rietveld refinements were
performed using Topas version 4.2 software (Bruker). A Shimadzu UV-2550 spectrophotometer was
used to record UV-visible spectra. Samples were analysed in solution utilizing a quartz cuvette with a
path length of 1 cm. Steady state fluorescence spectra were recorded on a Varian Eclipse
spectrofluorimeter where the samples were analysed in solution utilizing a quartz cuvette with a path
length of 1 cm. Phthalocyanine (and UCNP downconversion) lifetime measurements were undertaken
using a time correlated single photon counting setup (FluoTime 200, PicoQuant) and excite the samples
with a laser diode (LDH-P-670 with PDL 800-B, PicoQuant GmbH, 672 nm, 20 MHz repetition rate).
Fluorescence was detected under the magic angle with a Peltier cooled photomultiplier tube (PMT)
(PMA-C-192-N-M,
PicoQuant)
and
integrated
electronics
(PicoHarp
300E,
PicoQuant).
A
monochromator with a spectral width of about 4 nm was used to select the required emission
wavelength band. The response function of the system, which was measured with a scattering Ludox
solution (DuPont), had a full width at half-maximum (FWHM) of about 200 ps. All luminescence decay
curves were measured at the maximum of the emission peak. The data were analysed with the program
FluoFit (PicoQuant). The support plane approach was used to estimate the errors of the decay times.
Upconversion and singlet oxygen steady state and lifetime measurements were recorded using a time
correlated single photon counting setup with continuous wave (cw) and flash lamp extension
(FluoTime300, PicoQuant). Upconversion emissions were induced using a LDH-D-C-980 diode laser
(972 nm, 20 mW pulsed mode, 180 mW cw mode, PicoQuant). Steady state emission spectra were
obtained under cw excitation while time resolved measurements were performed using the burst mode
with a maximum pulse width of 500 ps. Emissions were detected under the magic angle utilizing a PMA-
C 192-M-N photomultiplier tube (PicoQuant). Singlet oxygen steady state and lifetime measurements
were undertaken using a laser diode in burst mode (LDH-P-670 with PDL 800-B, PicoQuant GmbH,
672 nm). Detection was performed under the magic angle using an H10330A-45 NIR photomultiplier
tube (Hamamatsu). Photon counting was done using an integrated TimeHarp 260 NANO TCSPC card
(PicoQuant). The emission from the visible to the NIR spectral range were selectively detected using
an Omni-λ300 monochromator with two interchangeable gratings (1200 lines/mm blazed at 500 nm for
the visible range and 600 lines/mm blazed at 1250 nm for the NIR spectral range) in combination with
motorized slits giving a tunable spectral width between 0.1 nm to 10.4 mm. Thermogravimetric analysis
was performed using a Shimadzu DTG-60A simultaneous differential thermal analysis –
thermogravimetric analysis system. Data were collected from 50 oC to 500 oC in an aluminium pan with
a nitrogen flow rate of 120 cm 3.min-1. Fourier transform infrared spectroscopy (FT-IR) was performed
using a Perkin Elmer Spectrum 100 ATR FT-IR spectrometer.
Photophysical parameters
Fluorescence quantum yields were calculated using the standard comparison method with Equation 1
(Fery-Forgues, 1999) where unsubstituted ZnPc was used as a standard in toluene with Ф F values of
0.07 (Ogunsipe et al. 2003). The standard and sample absorbencies at the vibronic band were kept the
same and excitation was done using the wavelength of the cross over point between the vibronic bands
of the sample and standard absorbance spectra.
ΦF = ΦStd
F. AStd .𝑛2
2
FStd . A .𝑛Std
(1)
Here, ΦF is the quantum yield of the sample and ΦStd that of the standard; F and Fstd represent the area
under the fluorescence emission curve for the sample and standard respectively; A and Astd refer to the
absorbance of the sample and standard and n and nStd are the refractive indices of the sample and
standard solutions, respectively.
The quenching of fluorescence lifetimes may be explained using fluorescence radiative
lifetimes (0) which were calculated using equation 2 (Geddes and Lakowicz 2005):
0 = F/F
(2)
a)
c)
b)
Fig. 2. Absorption spectra of a) H2Pc, b) Na(Y,Gd)F4:Yb/Er(spheres) and c) the Na(Y,Gd)F4:Yb/Er
(spheres) – H2Pc mix in toluene.
a)
c)
b)
Fig. 3. Absorbance (a), emission (b) and excitation (c) spectra of Na(Y,Gd)F4:Yb/Er(spheres)-H2Pc
mix in toluene.
a)
b)
c)
Fig. 4. Time resolved spectra of 1O2 produced by a) the H2Pc alone (in toluene), b) the H2Pc alone (in
DMSO) and c) the H2Pc (in DMSO) and sodium azide. H2Pc exc was at 672 nm with 1O2 emission
detection at 1270 nm.
a)
b)
Fig. 5. Time resolved spectra of the 1O2 produced by a) UCNP(star)-H2Pc mix and b) the star shaped
UCNPs alone, in toluene. H2Pc exc was at 672 nm with 1O2 emission detection at 1270 nm.
References
Fery-Forgues S, Lavabre D (1999) Are fluorescence quantum yields so tricky to measure? A
demonstration using familiar stationery products Journal of Chemical Education 76: 1260-1264.
Geddes CD, Lakowicz JR (Eds.) (2005) Topics in Fluorescence Spectroscopy, Springer, New York.
Ogunsipe A, Maree D, Nyokong T (2003) Solvent effects on the photophysical and fluorescence
properties of zinc phthalocyanine derivatives Journal of Molecular Structure 650: 131-140.