Design of diethynyl porphyrin derivatives with high near infrared fluorescence quantum yields

Article abstract of DOI:10.1142/S1088424614501107

A design strategy for (porphinato)zinc-based fluorophores that possess large near infrared fluorescence quantum yields is described. These fluorophores are based on a (5,15-diethynylporphinato)zinc(II) framework and feature symmetric donor or acceptor uni

Full text of DOI:10.1142/S1088424614501107

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2014; 18: 1–14
DOI: 10.1142/S1088424614501107
Published at http://www.worldscinet.com/jpp/
Design of diethynyl porphyrin derivatives with high near
infrared fluorescence quantum yields
Kimihiro Susumua,c,d and Michael J.Therien*b◊
a Department of Chemistry, 231 South 34th Street, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
b Department of Chemistry, French Family Science Center, 124 Science Drive, Duke University, Durham,
NC 27708-0346, USA
Dedicated to Professor Shunichi Fukuzumi on the occasion of his retirement
Received 6 October 2014
Accepted 11 November 2014
ABSTRACT: A design strategy for (porphinato)zinc-based fluorophores that possess large near infrared
fluorescence quantum yields is described. These fluorophores are based on a (5,15-diethynylporphinato)
zinc(II) framework and feature symmetric donor or acceptor units appended at the meso-ethynyl positions
via benzo[c][1,2,5]thiadiazole moieties. These (5,15-bis(benzo[c][1′,2′,5′]thiadiazol-4′-ylethynyl)-10,20-
bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II)(4),(5,15-bis[4′-(N,N-dihexylamino)
benzo[c][1′,2′,5′]thiadiazol-7′-ylethynyl]-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]
porphinato)zinc(II) (5), (5,15-bis([7′-(4″-n-dodecyloxyphenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]
ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (6), (5,15-bis([7′-
([7″-(4″ꢀ′-n-dodecyloxyphenyl)benzo[c][1″,2″,5″]thiadiazol-4″-yl]ethynyl)benzo[c][1′,2′,5′]thiadiazol-
4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (7), 5,15-bis
([7′-(4″-N,N-dihexylaminophenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-
bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (8), and (5,15-bis([7′-(4″-N,N-
dihexylaminophenylethenyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-
dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (9) chromophores possess red-shifted absorption
and emission bands that range between 650 and 750 nm that bear distinct similarities to those of the
chlorophylls and structurally related molecules. Interestingly, the measured radiative decay rate constants
for these emitters track with the integrated oscillator strengths of their respective x-polarized Q-band
absorptions, and thus define an unusual family of high quantum yield near infrared fluorophores in which
emission intensity is governed by a simple Strickler–Berg dependence.
KEYWORDS: diethynylporphyrin, benzo[c][1,2,5]thiadiazole, near infrared, fluorescence quantum
yield, Strickler–Berg.
oscillator strengths and high fluorescence quantum
INTRODUCTION
yields are important to molecular imaging [1–5] and
The design and synthesis of near infrared (NIR)
solar energy conversion technologies [6–10]. Likewise,
absorption materials that possess large absorptive
the efficient utilization of NIR sunlight is a key feature
of natural photosynthesis, which exploits NIR-absorbing
◊SPP full member in good standing
dyes such as chlorophylls and pheophytins [11]. Relative
to the tremendous attention that has been paid to the
design and synthesis of low band gap chromophores
and materials [12–19], much less focus has been given
to the development of strategies that channel enhanced
oscillator strength into the low energy optical transitions
*Correspondence to: Michael J. Therien, tel: +1 919-660-1670,
email: michael.therien@duke.edu
Current address: c Optical Sciences Division, U.S. Naval
Research Laboratory, Washington, DC 20375, USA; d Sotera
Defense Solutions, Inc., Columbia, MD 21046, USA
Copyright © 2014 World Scientific Publishing Company

2
K. SUSUMU AND M. J. THERIEN
of such compositions. For example, only a limited number
of conjugated organic structures possess both high
oscillator strength NIR (S0→S1) absorptions and corres-
ponding high (S1→S0) fluorescence quantum yields [20,
21]. In general, a higher S0→S1 absorptive extinction
coefficient should correlate with a larger S1→S0
radiative rate constant, congruent with the Strickler–
Berg relationship [22]; most strongly absorbing organic
NIR dyes, however, are not impressive emitters, due in
many cases to large magnitude S1 state non-radiative rate
constants that are readily rationalized within the context
of the energy gap law [23].
Ethyne groups fused to the porphyrin meso-positions
provide significant electronic interaction with the
macrocyclea2u-derivedHOMOandremovethedegeneracy
of the low-lying empty eg orbitals [39, 42, 45, 50, 55]. Here
we report the synthesis and optical properties of conjugated
5,15-diethynyl(porphinato)zinc(II) complexes that feature
conjugated terminal groups having varying degrees of
proquinoidal character (Fig. 1) that drive intense Q-band
absorptions; the uncommon emissive properties of these
new fluorophores based on a (5,15-diethynylporphinato)
zinc(II) framework are discussed within the context of the
Strickler–Berg relationship.
Porphyrins are tetrapyrrole p-conjugated systems,
and the lowest energy absorption bands of simple
tetraphenylporphyrin or octaethylporphyrin monomers
range typically over the 600 to 650 nm spectral regime
and feature modest absorptive extinction coefficients
(e < 104 M-1.cm-1). Modification of the porphyrin p-skeleton
can further reduce the HOMO–LUMO gap; the electronic
structures of such reduced band gap porphyrins can in
general be rationalized using Gouterman’s four orbital
model [24]. In a simple (porphinato)metal complex having
D4h symmetry, the LUMO is doubly degenerate, and the
HOMO and HOMO-1 are nearly degenerate in energy;
as a result, substantial configuration interaction mixes
the (a1u→eg) and (a2u→eg) transitions. Constructive and
destructive combinations of these one-electron transitions
give rise to an intense shorter-wavelength Soret band and
a weakly absorbing longer-wavelength Q-band. While
removal of frontier orbital (HOMO/HOMO-1, LUMO/
LUMO+1)degeneracyisexpectedtoresultinaugmentation
of the Q-band absorptive extinction coefficient, relatively
few examples exist of low band gap porphyrin derivatives
that possess intense NIR Q-bands [25–29].
In contrast, the chlorophylls, natural porphyrin
derivatives, possesslowestenergyQ-bandswithsignificant
extinction coefficients (e: 0.5 ~ 1 × 105 M-1.cm-1) [30, 31];
some chlorophyll derivatives and related macrocycles
feature substantial fluorescence quantum yields that range
from ~0.05 to 0.3 [32, 33]. While significant strides have
been made in recent years regarding chlorophyll synthesis
[33–35], the more involved nature of their fabrication
limits many possible applications of these structures.
Chromophores within the phthalocyanine family also
exhibit intense low energy electronic absorption bands
(e: 1 ~ 2 × 105 M-1.cm-1); while a few examples of these
chromophores are known that feature both substantial
NIR absorptivity and significant fluorescence quantum
yield (0.1 ~ 0.8) [36, 37], it is important to point out
that extensive modulation of phthalocyanine absorptive
properties and photophysics is limited by the modest
frontier orbital electron density localized at the periphery
of the macrocycle-fused benzene rings [38].
EXPERIMENTAL
Materials
All manipulations were carried out under nitrogen
previously passed through an O2 scrubbing tower
(Schweitzerhall R3-11 catalyst) and a drying tower
(Linde 3-Å molecular sieves) unless otherwise stated.
Air sensitive solids were handled in a Braun 150-M
glove box. Standard Schlenk techniques were employed
to manipulate air-sensitive solutions. Tetrahydrofuran
(THF) was distilled from K/4-benzoylbiphenyl under N2.
Triethylamine and MeOH were distilled from CaH2 under
N2. The catalysts Pd(PPh3)4, Pd(PPh3)2Cl2, dichloro[1,1′-
bis(diphenylphosphino)ferrocene]palladium(II) dichlo-
romethane adduct, P(t-Bu)3 (10 wt% solution in hexanes),
tris(dibenzylideneacetone)dipalladium(0) (Pd2dba3),
CuI and triphenylarsine (AsPh3) were purchased from
Strem Chemicals and used as received. 4-Bromobenzo[c]
[1,2,5]thiadiazole, and 4,7-dibromobenzo[c][1,2,5]
thiadiazole were prepared by literature methods [98].
(5,15-Bis[trimethylsilylethynyl]-10,20-bis[3′,5′-bis(9″-
methoxy-1″,4″,7″-trioxanonyl)phenyl]porphinato)
zinc(II) (1), (5,15-dibromo-10,20-bis[2′,6′-bis(3″,3″-
dimethyl-1″-butyloxy)phenyl] porphinato)zinc(II), (5,15-
diethynyl-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-
butyloxy)phenyl]porphinato)zinc(II), and (5,15-bis(4′-
(N,N-dimethylamino)phenylethynyl)-10,20-bis[2′,6′-
bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)
zinc(II) (2) were synthesized as described previously [50,
54, 66]. A number of key precursors were synthesized
as reported earlier [99]. All NMR solvents, and all other
chemicals, were used as received.
1
Chemical shifts for H NMR spectra are relative to
the tetramethylsilane (TMS) signal in deuterated solvent
(TMS, d = 0.00 ppm). All J values are reported in Hertz.
Flash and size exclusion column chromatography were
performed on the bench top, using respectively silica
gel (EM Science, 230–400 mesh) and Bio-Rad Bio-
Beads SX-1 as media. CI mass spectra were acquired
at the Mass Spectrometry Center at the University
of Pennsylvania. MALDI-TOF mass spectroscopic
data were obtained with a Voyager-DE RP instrument
We have explored synthesis and electronic properties of
meso-ethynyl porphyrin derivatives [39–62] for nonlinear
optics [60, 63–81], optoelectronic devices [82–87], and
fluorescence-based optical imaging technologies [88–97].
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 2–14

DESIGN OF DIETHYNYL PORPHYRIN DERIVATIVES WITH HIGH NEAR INFRARED FLUORESCENCE QUANTUM YIELDS
3
Fig. 1. Structures of the TMS-protected (5,15-diethynyl-10,20-bis[3′,5′-bis(9′′-methoxy-1′′,4′′,7′′-trioxanonyl)phenyl]porphinato)
zinc(II) reference monomer (1), and NIR fluorophores 2–9
(PerSeptive Biosystems); samples for these experiments
were prepared as micromolar solutions in either CH2Cl2
or THF, and dithranol (Sigma–Aldrich) was utilized as
the matrix.
in number of photons), A is the absorbance at the
excitation wavelength, and n is the refractive index of the
solvents used. Subscripts s and r refer to the sample and
reference, respectively. Time-correlated single-photon
counting (TCSPC) experiments to measure fluorescence
lifetimes were performed using an Edinburgh Analytical
Instruments FL/FS 900 spectrofluorimeter. The excit-
ation sources for TCSPC measurements were either a
nanosecond flash lamp operating under an atmosphere
of H2 gas (0.50–0.55 bar, 0.7 nm fwhm, 40 kHz
repetition rate) or a blue (450 15 nm) light-emitting
diode (Picoquant PLS 450/PDL 800-B) triggered at a
frequency of 100 kHz by a Berkeley Nucleonics 555
pulse generator. TCSPC data were analyzed by iterative
convolution of the fluorescence decay profile with the
instrument response function using software provided by
Edinburgh Instruments.
Instrumentation
1H NMR spectra were recorded on either 250 MHz
AC-250, 300 MHz DMX-300, or 500 MHz AMX-
500 Brüker spectrometers. Electronic absorption
spectra were recorded on a Shimadzu PharmaSpec
UV1700 spectrophotometer. Fluorescence spectra were
obtained with a Spex Fluorolog-3 spectrophotometer
(Jobin Yvon Inc., Edison, NJ) that utilized a T-channel
configuration with red sensitive R2658 Hamamatsu
PMT and liquid nitrogen cooled InGaAs detectors. The
obtained fluorescence spectra were corrected using the
spectral output of a calibrated light source supplied by
the National Bureau of Standards. Fluorescence quantum
yields were measured on N2-purged solutions at room
temperature. Tetraphenylporphyrin in benzene (Ff =
0.13) was used as a standard [100]. The fluorescence
quantum yields of each sample were calculated using the
following equation (Equation 1)
Synthesis
(5,15-Bis[4′-(4″-N,N-dihexylaminophenylethynyl)
phenylethynyl]-10,20-bis[2′,6′-bis(3″,3″-dimethyl-
1″-butyloxy)phenyl]porphinato)zinc(II) (3). 1-(4′-N,
N-dihexylaminophenylethynyl)-4-iodobenzene [99]
(55.5mg,1.14×10-4mol),(5,15-diethynyl-10,20-bis[2′,6′-
bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)
zinc(II) (50.4 mg, 5.17 × 10-5 mol), Pd(PPh3)4 (13.2 mg,
1.14 × 10-5 mol), CuI (1.0 mg, 5.3 × 10-6 mol) and dry THF
(7.0 mL) were added to a 100-mL round-bottom flask. Ar
was bubbled into the reaction mixture for 5 min before
F ⋅ Ar ⋅ns2
Ff (s)
s
=
(1)
Ff (r) F ⋅ As ⋅nr2
r
where Ff is the fluorescence quantum yield, F is the
area under the corrected fluorescence band (expressed
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 3–14

4
K. SUSUMU AND M. J. THERIEN
piperidine (0.50 mL) was added.The reaction mixture was
stirred at 45°C for 3.5 h under Ar. After the solvent was
evaporated, the residue was chromatographed on silica
gel with 8:1 hexanes:THF as the eluent. Yield 0.063 g
(72% based on 50.4 mg of (5,15-diethynyl-10,20-
bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]
residue was chromatographed on silica gel column with
5:1 hexanes:THF as the eluent. The product was further
purified by size exclusion column chromatography (Bio
Rad Bio-Beads SX-1 packed in THF, gravity flow). Yield
40.7 mg (50% based on 71.0 mg of (5,15-dibromo-10,20-
bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphi-
1
1
porphinato)zinc(II)). H NMR (300 MHz; CDCl3): d,
nato)zinc(II)). H NMR (300 MHz; CDCl3): d, ppm
ppm 9.67 (d, 4H, J = 4.6 Hz, b-H), 8.86 (d, 4H, J = 4.6 Hz,
b-H), 7.96 (d, 4H, J = 8.4 Hz, Ph-H), 7.72 (t, 2H, J =
8.4 Hz, Ph-H), 7.65 (d, 4H, J = 8.4 Hz, Ph-H), 7.43 (d,
4H, J = 8.8 Hz, Ph-H), 7.02 (d, 4H, J = 8.5 Hz, Ph-H),
6.61 (d, 2H, J = 9.0 Hz, Ph-H), 3.92 (t, 8H, J = 7.3 Hz,
–O–CH2–C), 3.30 (t, 8H, J = 7.6 Hz, –N–CH2–C), 1.60
(m, 8H, –N–C–CH2–C), 1.2–1.4 (m, 24H, –CH2–), 0.92
(t, 8H, J = 6.8 Hz, O–C–CH2–), 0.89 (t, 12H, J = 7.3 Hz,
–CH3), 0.27 (s, 36H, –C–CH3). MS (MALDI-TOF): m/z
1690.92 (calcd. for [M]+ 1690.976).
4-(Trimethylsilylethynyl)benzo[c][1,2,5]thia-
diazole. 4-Bromobenzo[c][1,2,5]thiadiazole (0.378 g,
1.76 ×ꢀ10-3 mol), Pd(PPh3)4 (0.125 g, 1.08 × 10-4 mol), CuI
(14 mg, 7.4 × 10-5 mol) and dry THF (20 mL) were added
to a 100-mL round-bottom flask. Ar was bubbled into
the reaction mixture for 5 min before diisopropylamine
(1.0 mL) and (trimethylsilyl)acetylene (1.00 mL, 7.1 ×
10-3 mol) were added. The reaction mixture was stirred
at 45°C for 11 h under Ar. After cooling, the solvent was
evaporated. The residue was chromatographed on silica
gel column with 1:1 hexanes:CHCl3 as the eluent. Yield
0.406 g (99% based on 0.378 g of 4-bromobenzo[c]
[1,2,5]thiadiazole). 1H NMR (300 MHz; CDCl3): d, ppm
7.99 (dd, 1H, J = 1.0, 8.8 Hz, Ph-H), 7.77 (dd, 1H, J =
1.0, 7.0 Hz, Ph-H), 7.55 (dd, 1H, J = 7.0, 8.8 Hz, Ph-H),
0.34 (s, 9H, –Si–CH3). MS (CI): m/z 232.048 (calcd. for
[M]+ 232.049).
4-Ethynylbenzo[c][1,2,5]thiadiazole. 4-(Trimethyl-
silylethynyl)benzo[c][1,2,5]thiadiazole (0.100 g, 4.30 ×
10-4 mol), K2CO3 (78.6 mg, 5.7 × 10-4 mol), THF (3.0 mL),
and MeOH (2.0 mL) were added to a 100-mL round-
bottom flask. The reaction mixture was stirred at room
temperature for 1.5 h under Ar. The reaction mixture was
filtered and the solvent was evaporated. Yield quanti-
tative. 1H NMR (300 MHz; CDCl3): d, ppm 8.04 (d, 1H,
J = 8.8 Hz, Ph-H), 7.81 (d, 1H, J = 6.9 Hz, Ph-H), 7.58
(t, 1H, J = 8.0 Hz, Ph-H), 3.59 (s, 1H, ethynyl-H). MS
(CI): m/z 160.009 (calcd. for [M]+ 160.010).
(5,15-Bis(benzo[c][1,2,5]thiadiazol-4-ylethynyl)-
10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)
phenyl]-porphinato)zinc(II) (4). 4-Ethynylbenzo[c]
[1,2,5]thiadiazole (40.0 mg, 2.50 × 10-4 mol), (5,15-
dibromo-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-
butyloxy)phenyl]porphinato)zinc(II) (71.0 mg, 2.50 ×
10-4 mol), Pd(PPh3)4 (22.6 mg, 2.0 × 10-5 mol), CuI
(2.0 mg, 1.1 × 10-5 mol) and dry THF (10 mL) were added
to a 100-mL round-bottom flask. Ar was bubbled into the
reactionmixturefor5minbeforepiperidine(0.50mL)was
added. The reaction mixture was stirred at 48°C for 24 h
under Ar. After cooling, the solvent was evaporated. The
9.91 (d, 4H, J = 4.5 Hz, b-H), 8.87 (d, 4H, J = 4.5 Hz,
b-H), 8.18 (d, 2H, J = 7.0 Hz, Ph-H), 8.07 (d, 2H, J =
8.8 Hz, Ph-H), 7.76 (dd, 2H, J = 7.0, 8.8 Hz, Ph-H),
7.72 (t, 2H, J = 8.4 Hz, Ph-H), 7.03 (d, 4H, J = 8.4 Hz,
Ph-H), 3.92 (t, 8H, J = 7.6 Hz, –O–CH2–C), 0.83 (t, 8H,
J = 7.5 Hz, –O–C–CH2–C), 0.37 (s, 36H, –C–CH3). MS
(MALDI-TOF): m/z 1240.7 (calcd. for [M]+ 1240.441).
(5,15-Bis[4′-(N,N-dihexylamino)benzo[c][1′,2′,5′]
thiadiazole-7′-ylethynyl]-10,20-bis[2′,6′-bis(3″,3″-
dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (5).
4-Bromo-7-(N,N-dihexylamino)benzo[c][1,2,5]thiadia-
zole [99] (53.8 mg, 1.35 × 10-4 mol), (5,15-diethynyl-
10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]
porphinato)zinc(II) (41.0 mg, 4.2 × 10-5 mol), Pd(PPh3)4
(12.8 mg, 1.1 × 10-5 mol), CuI (1.1 mg, 5.8 × 10-6 mol) and
dry THF (5.0 mL) were added to a 100-mL round-bottom
flask. Ar was bubbled into the reaction mixture for 5 min
before piperidine (0.20 mL) was added. The reaction
mixture was stirred at 45°C for 24 h under Ar. After the
solvent was evaporated, the residue was chromatographed
on silica gel with 8:1 hexanes: THF as the eluent. Yield
22.0 mg (33% based on 41.0 mg of (5,15-diethynyl-
10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)
phenyl]porphinato)zinc(II)). 1H NMR (300 MHz;
CDCl3): d, ppm 9.94 (d, 4H, J = 4.6 Hz, b-H), 8.86 (d,
4H, J = 4.6 Hz, b-H), 8.07 (d, 2H, J = 8.2 Hz, Ph-H), 7.70
(t, 2H, J = 8.4 Hz, Ph-H), 7.00 (d, 4H, J = 8.5 Hz, Ph-H),
6.59 (d, 2H, J = 8.3 Hz, Ph-H), 3.91 (t, 8H, J = 7.2 Hz,
–O–CH2–C), 3.86 (t, 8H, J = 8.3 Hz, –N–CH2–C), 1.79
(m, 8H, –N–C–CH2–C), 1.1–1.5 (m, 24H, –CH2–), 0.94
(t, 8H, J = 7.0 Hz, O–C–CH2–), 0.88 (t, 12H, J = 7.2 Hz,
–CH3), 0.26 (s, 36H, –C–CH3). MS (MALDI-TOF): m/z
1607.08 (calcd. for [M]+ 1606.838).
4-Bromo-7-(4′-n-dodecyloxyphenylethynyl)
benzo[c][1,2,5]thiadiazole. 4-n-Dodecyloxyethynylben-
zene [99] (0.620 g, 2.16 × 10-3 mol), 4,7-dibromobenzo[c]
[1,2,5]thiadiazole (1.91 g, 6.50 × 10-3 mol), Pd(PPh3)2Cl2
(0.162 g, 2.31 × 10-4 mol), CuI (21 mg, 1.1 × 10-4 mol),
and dry toluene (10 mL) were added to a 100-mL
round-bottom flask. Ar was bubbled into the reaction
mixture for 5 min before triethylamine (10 mL) was
added. The reaction mixture was stirred at 45°C for 3 h
under Ar. After the solvent was evaporated, the reaction
mixture was chromatographed on silica gel with 2:1
hexanes:CH2Cl2. Yield 0.496 g (46% based on 0.620 g
of 4-n-dodecyloxyethynylbenzene). 1H NMR (300 MHz;
CDCl3): d, ppm 7.83 (d, 1H, J = 7.6 Hz, Ph-H), 7.63 (d,
1H, J = 7.6 Hz, Ph-H), 7.59 (d, 2H, J = 8.9 Hz, Ph-H),
6.91 (d, 2H, J = 8.9 Hz, Ph-H), 3.99 (t, 2H, J = 6.6 Hz,
–OCH2–), 1.80 (quint, 2H, –OC–CH2–), 1.45 (m, 2H,
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 4–14

DESIGN OF DIETHYNYL PORPHYRIN DERIVATIVES WITH HIGH NEAR INFRARED FLUORESCENCE QUANTUM YIELDS
5
–CH2–), 1.2–1.4 (m, 16H, –CH2–), 0.88 (t, 3H, J = 6.7 Hz,
–CH3). MS (CI): m/z 498.133 (calcd. for [M]+ 498.134).
(5,15-Bis([7′-(4″-n-dodecyloxyphenylethynyl)
benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-
bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]
porphinato)zinc(II) (6). 4-Bromo-7-(4′-n-dodecyloxy-
phenylethynyl)benzo[c][1,2,5]thiadiazole (40.9 mg,
8.19 × 10-5 mol), (5,15-diethynyl-10,20-bis[2′,6′-bis-
(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II)
(35.7 mg, 3.66 × 10-5 mol), Pd(PPh3)4 (10.1 mg, 8.7 ×
10-6 mol), CuI (1.3 mg, 6.8 × 10-6 mol), and dry THF
(6.0 mL) were added to a 100-mL round-bottom flask.
Ar was bubbled into the reaction mixture for 10 min
before piperidine (0.50 mL) was added. The reaction
mixture was stirred at 44°C for 17.5 h under Ar. After
cooling, the solvent was evaporated. The residue was
chromatographed on silica gel with 5:1 hexanes:THF
as the eluent. The product was further purified by size
exclusion column chromatography (BioRad Bio-Beads
SX-1 packed in THF, gravity flow). Yield 45.5 mg (69%
based on 35.7 mg of 5,15-diethynyl-10,20-bis[2′,6′-
bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)
(0.347 g, 2.51 × 10-3 mol), DMF (25 mL), and H2O
(3.0 mL) were added to a 100-mL round-bottom flask.
Ar was bubbled into the reaction mixture for 5 min at
room temperature. The reaction mixture was warmed
up to 86°C and stirred for 7.5 h under Ar. After cooling,
200 mL of dilute aq. HCl was added to the reaction
mixture, and the product was extracted with CHCl3 and
dried over Na2SO4. The solvent was evaporated, and
the residue was chromatographed on silica gel with 1:1
hexanes:CHCl3. The product was further purified by size
exclusion column chromatography (BioRad Bio-Beads
SX-1 packed in THF, gravity flow). Yield 0.295 g (77%
based on 0.313 g of 4-n-dodecyloxyphenyl-4′,4′,5′,5′-
tetramethyl-1′,3′,2′-dioxaborolane). 1H NMR (300 MHz;
CDCl3): d, ppm 7.90 (d, 1H, J = 7.6 Hz, –CH2–), 7.85 (d,
2H, J = 8.8 Hz, Ph-H), 7.53 (d, 1H, J = 7.6 Hz, Ph-H),
7.05 (d, 2H, J = 8.8 Hz, Ph-H), 4.04 (t, 2H, J = 6.5 Hz,
–OCH2–), 1.83 (quint, 2H, J = 6.5 Hz, –OC–CH2–), 1.49
(m, 2H, –CH2–), 1.2–1.4 (m, 16H, –CH2–), 0.88 (t, 3H,
J = 6.6 Hz, –CH3). MS (CI): m/z 474.133 (calcd. for
[M]+ 474.134).
4-(4′-n-Dodecyloxyphenyl)-7-(trimethylsilyl-
ethynyl)benzo[c][1,2,5]thiadiazole. 4-Bromo-7-(4′-n-
dodecyloxyphenyl)benzo[c][1,2,5]thiadiazole (0.2364 g,
4.97 × 10-4 mol), Pd(PPh3)4 (55.4 mg, 4.79 × 10-5 mol),
CuI (3.4 mg, 1.8 × 10-5 mol), and dry THF (10 mL)
were added to a 100-mL round-bottom flask. Ar was
bubbled into the reaction mixture for 5 min before
(trimethylsilyl)acetylene (0.25 mL, 1.8 × 10-3 mol) and
diisopropylamine (1.0 mL) were added. The reaction
mixture was stirred at 50°C for 17.5 h under Ar. After
cooling, the solvent was evaporated. The residue was
chromatographed on silica gel with 8:1 hexanes:THF.
Yield 0.240 g (98% based on 0.2364 g of 4-bromo-7-
(4′-n-dodecyloxyphenyl)benzo[c][1,2,5]thiadiazole).
1H NMR (300 MHz; CDCl3): d, ppm 7.90 (d, 2H, J =
8.9 Hz, Ph-H), 7.82 (d, 1H, J = 7.4 Hz, Ph-H), 7.61
(d, 1H, J = 7.4 Hz, Ph-H), 7.05 (d, 2H, J = 8.9 Hz,
Ph-H), 4.04 (t, 2H, J = 6.5 Hz, –OCH2–), 1.82 (quint, 2H,
J = 6.9 Hz, –OC–CH2–), 1.49 (m, 2H, –CH2–), 1.2–1.4
(m, 16H, –CH2–), 0.88 (t, 3H, J = 6.7 Hz, –CH3), 0.34
(s, 9H, –Si–CH3). MS (CI): m/z 493.272 (calcd. for [M +
H]+ 493.271).
1
zinc(II)). H NMR (300 MHz; 1 drop pyridine-d5 in
CDCl3): d, ppm 9.90 (d, 4H, J = 4.6 Hz, b-H), 8.86 (d,
4H, J = 4.6 Hz, b-H), 8.15 (d, 2H, J = 7.4 Hz, Ph-H),
7.92 (d, 2H, J = 7.4 Hz, Ph-H), 7.72 (t, 2H, J = 8.4 Hz,
Ph-H), 7.65 (d, 4H, J = 8.8 Hz, Ph-H), 7.03 (d, 4H, J =
8.5 Hz, Ph-H), 6.94 (d, 4H, J = 8.9 Hz, Ph-H), 4.01 (t,
4H, J = 6.6 Hz, –O–CH2–C), 3.93 (t, 8H, J = 7.5 Hz, –O–
CH2–C), 1.82 (quint, 4H, J = 6.8 Hz, –O–CH2–C), 1.48
(m, 4H, –CH2–), 1.15–1.40 (m, 32H, –CH2–), 0.89 (t, 6H,
J = 6.7 Hz, –CH3), 0.83 (t, 8H, J = 7.5 Hz, –OC–CH2–),
0.37 (s, 36H, –C–CH3). MS (MALDI-TOF): m/z 1809.0
(calcd. for [M]+ 1808.869).
4-n-Dodecyloxyphenyl-4′,4′,5′,5′-tetramethyl-
1′,3′,2′-dioxaborolane. 4-n-Dodecyloxyiodobenzene
[99] (1.00 g, 2.58 × 10-3 mol), dichloro[1,1′-bis(diphenyl-
phosphino)ferrocene]palladium(II)∙dichloromethane
adduct (0.106 g, 1.30 × 10-4 mol) were added to 1,2-
dichloroethane(5.0mL)andEt3N(1.0mL, 7.2×10-3 mol).
4,4,5,5-Tetramethyl-1,3,2-dioxaborolane (0.56 mL, 3.9 ×
10-3 mol) was added, and the reaction mixture was stirred
at 75°C for 1.5 h under Ar. After cooling, the solvent was
evaporated. The residue was chromatographed on silica
gel with 2:1 hexanes:CHCl3 as the eluent. Yield 0.674 g
(67% based on 1.00 g of 4-n-dodecyloxyiodobenzene).
1H NMR (250 MHz; CDCl3): d, ppm 7.73 (d, 2H, J =
8.7 Hz, Ph-H), 6.88 (d, 2H, J = 8.7 Hz, Ph-H), 3.97 (t,
2H, J = 6.6 Hz, –OCH2–), 1.78 (quint, 2H, J = 6.6 Hz,
–OC–CH2–), 1.45 (m, 2H, –CH2–), 1.33 (s, 12H, –CH3),
1.26 (m, 16H, –CH2–), 0.88 (t, 3H, J = 6.5 Hz, –CH3).
MS (CI): m/z 388.317 (calcd. for [M]+ 388.315).
4-(4′-n-Dodecyloxyphenyl)-7-ethynylbenzo[c][1,2,5]
thiadiazole.4-(4′-n-Dodecyloxyphenyl)-7-(trimethylsilyl-
ethynyl)benzo[c][1,2,5]thiadiazole (0.223 g, 4.53 ×
10-4 mol) was dissolved in a mixture of THF (7.0 mL)
and MeOH (3.0 mL). K2CO3 (85 mg, 6.2 × 10-4 mol) was
added, and the reaction mixture was stirred for 2 h under
Ar. The reaction mixture was filtered and the filtrate
evaporated. Yield 0.190 g (99.7% based on 0.223 g of
4-(4′-n-dodecyloxyphenyl)-7-(trimethylsilylethynyl)
benzo[c][1,2,5]thiadiazole). 1H NMR (300 MHz;
CDCl3): d, ppm 7.90 (d, 2H, J = 8.9 Hz, Ph-H), 7.86 (d,
1H, J = 7.3 Hz, Ph-H), 7.63 (d, 1H, J = 7.4 Hz, Ph-H),
7.06 (d, 2H, J = 8.9 Hz, Ph-H), 4.04 (t, 2H, J = 6.5 Hz,
–OCH2–), 3.60 (s, 1H, ethynyl-H), 1.83 (quint, 2H,
4-Bromo-7-(4′-n-dodecyloxyphenyl)benzo[c][1,2,5]
thiadiazole. 4-n-Dodecyloxyphenyl-4′,4′,5′,5′-tetra-
methyl-1′,3′,2′-dioxaborolane (0.313 g, 8.06 × 10-4 mol),
4,7-dibromobenzo[c][1,2,5]thiadiazole (0.474 g, 1.61 ×
10-3 mol), Pd(PPh3)4 (97 mg, 8.4 × 10-5 mol), K2CO3
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 5–14

6
K. SUSUMU AND M. J. THERIEN
J = 6.9 Hz, –OC–CH2–), 1.49 (m, 2H, –CH2–), 1.2–1.4
(m, 16H, –CH2–), 0.88 (t, 3H, J = 6.7 Hz, –CH3). MS
(ESI): m/z 421.233 (calcd. for [M + H]+ 421.231).
4H, J = 6.4 Hz, –O–CH2–C), 3.94 (t, 8H, J = 7.5 Hz, –O–
CH2–C), 1.85 (quint, 4H, J = 7.0 Hz, –O–CH2–C), 1.50
(m, 4H, –CH2–), 1.15–1.40 (m, 32H, –CH2–), 0.89 (t, 6H,
–CH3), 0.85 (t, 8H, J = 7.5 Hz, –OC–CH2–), 0.39 (s, 36H,
–C–CH3). MS (MALDI-TOF): m/z 2076.99 (calcd. for
[M]+ 2076.857).
4-([4′-(4″-n-Dodecyloxyphenyl)benzo[c][1′,2′,5′]
thiadiazol-7′-yl]ethynyl)-7-iodobenzo[c][1,2,5]thiadia-
zole. 4-(4′-n-Dodecyloxyphenyl)-7-ethynylbenzo[c]
[1,2,5]thiadiazole (0.120 g, 2.85 × 10-4 mol), 4,7-diiodo-
benzo[c][1,2,5]thiadiazole [99] (0.232 g, 5.98 × 10-4 mol),
Pd2dba3 (32.8 mg, 3.6 × 10-5 mol), AsPh3 (92.4 mg, 3.0 ×
10-4 mol), and dry THF (15 mL) were added to a 100-mL
round-bottom flask. Ar was bubbled into the reaction
mixture for 5 min before diisopropylethylamine (1.0 mL)
was added. The reaction mixture was stirred at 48°C for
12.5 h underAr.After cooling, the solvent was evaporated.
The residue was chromatographed on silica gel with 8:1
hexanes:THF. The product was further purified by size
exclusion column chromatography (BioRad Bio-Beads
SX-1 packed in THF, gravity flow). Yield 69.8 mg
(36% based on 0.120 g of 4-(4′-n-dodecyloxyphenyl)-7-
ethynylbenzo[c][1,2,5]thiadiazole). 1H NMR (300 MHz;
CDCl3): d, ppm 8.16 (d, 1H, J = 7.5 Hz, Ph-H), 8.03 (d,
1H, J = 7.4 Hz, Ph-H), 7.96 (d, 2H, J = 8.9 Hz, Ph-H), 7.71
(d, 1H, J = 7.4 Hz, Ph-H), 7.70 (d, 1H, J = 7.5 Hz, Ph-H),
7.08 (d, 2H, J = 8.9 Hz, Ph-H), 4.05 (t, 2H, J = 6.5 Hz,
–OCH2–), 1.84 (quint, 2H, J = 7.0 Hz, –OC–CH2–),
1.49 (m, 2H, –CH2–), 1.2–1.4 (m, 16H, –CH2–), 0.88 (t,
3H, J = 6.6 Hz, –CH3). MS (MALDI-TOF): m/z 680.09
(calcd. for [M]+ 680.110).
5,15-Bis([7′-(4′′-N,N-dihexylaminophenylethynyl)
benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-
bis[2′,6′-bis(3′′,3′′-dimethyl-1′′-butyloxy)phenyl]
porphinato)zinc(II) (8). 4-(4′-N,N-Dihexylamino-
phenylethynyl)-7-iodobenzo[c][1,2,5]thiadiazole [99]
(73.6 mg,1.35×10-4 mol),5,15-diethynyl-10,20-bis[2′,6′-
bis(3′′,3′′-dimethyl-1′′-butyloxy)phenyl]porphinato)
zinc(II) (59.0 mg, 6.05 × 10-5 mol), Pd(PPh3)4 (15.6 mg,
1.35 × 10-5 mol), CuI (1.0 mg, 5.3 × 10-6 mol), and dry
THF (6.0 mL) were added to a 100-mL round-bottom
flask. Ar was bubbled into the reaction mixture for 5 min
before piperidine (0.50 mL) was added. The reaction
mixture was stirred at 49°C for 20 h under Ar. After
cooling, the solvent was evaporated. The residue was
chromatographed on silica gel with 5:1 hexanes:THF
as the eluent. The product was further purified by size
exclusion column chromatography (BioRad Bio-Beads
SX-1 packed in THF, gravity flow). Yield 0.107 g (98%
based on 59.0 mg of 5,15-diethynyl-10,20-bis[2′,6′-
bis(3′′,3′′-dimethyl-1′′-butyloxy)phenyl]porphinato)
1
zinc(II)). H NMR (300 MHz; CDCl3): d, ppm 9.99 (d,
4H, J = 4.6 Hz, b-H), 8.94 (d, 4H, J = 4.6 Hz, b-H), 8.17
(d, 2H, J = 7.4 Hz, Ph-H), 7.89 (d, 2H, J = 7.4 Hz, Ph-H),
7.73 (t, 2H, J = 8.4 Hz, Ph-H), 7.56 (d, 4H, J = 7.7 Hz,
Ph-H), 7.03 (d, 4H, J = 8.5 Hz, Ph-H), 6.64 (d, 4H, J =
9.0 Hz, Ph-H), 3.94 (t, 8H, J = 7.3 Hz, –O–CH2–C), 3.32
(t, 8H, J = 7.6 Hz, –N–CH2–C), 1.5–1.7 (m, 4H, –CH2–),
1.25–1.45 (m, 24H, –CH2–), 0.8–1.0 (m, 20H, –O–C–
CH2– and –CH3), 0.26 (s, 36H, –C–CH3). MS (MALDI-
TOF): m/z 1807.1 (calcd. for [M]+ 1806.901).
(5,15-Bis([7′-([7″-(4′″-n-dodecyloxyphenyl)benzo
[c][1″,2″,5″]thiadiazol-4″-yl]ethynyl)benzo[c]-
[1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-
bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)
zinc(II) (7). 4-([4′-(4″-n-Dodecyloxyphenyl)benzo[c]
[1′,2′,5′]thiadiazol-7′-yl]ethynyl)-7-iodobenzo[c][1,2,5]
thiadiazole (31.0 mg, 4.55 × 10-5 mol), 5,15-diethynyl-
10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)
phenyl]porphinato)zinc(II) (22.2 mg, 2.28 × 10-5 mol),
Pd(PPh3)4 (9.1 mg, 7.9 × 10-6 mol), CuI (1.7 mg, 8.9 ×
10-6 mol), and dry THF (8.0 mL) were added to a
100-mL round-bottom flask. Ar was bubbled into the
reaction mixture for 5 min before piperidine (0.50 mL)
was added. The reaction mixture was stirred at 50°C
for 3.5 h under Ar. After cooling, the solvent was
evaporated. The residue was chromatographed on
silica gel with 3:1 hexanes:THF as the eluent. The
product was further purified by size exclusion column
chromatography (BioRad Bio-Beads SX-1 packed
in THF, gravity flow). Yield 30.2 mg (64% based on
31.0 mg of 4-([4′-(4′′-n-dodecyloxyphenyl)benzo[c]
[1′,2′,5′]thiadiazol-7′-yl]ethynyl)-7-iodobenzo[c][1,2,5]
4-(4′-(N,N-Dihexylamino)phenylethenyl)-7-iodo-
benzo[c][1,2,5]thiadiazole. N,N-Dihexylamino-4-vinyl-
benzene[99](0.154g,5.36×10-4 mol),4,7-diiodobenzo[c]
[1,2,5]thiadiazole [99] (0.309 g, 7.96 × 10-4 mol),
Pd2dba3 (50.4 mg, 5.5 × 10-5 mol), and dry 1,4-dioxane
(7.0 mL) were added to a 100-mL round-bottom flask.
Ar was bubbled into the reaction mixture for 5 min
before dicyclohexylmethylamine (0.50 mL) and P(t-Bu)3
(10 wt% in hexanes, 1.00 mL, 3.3 × 10-4 mol) were
added. The reaction mixture was stirred at 57°C for 48 h
under Ar. After the solvent was evaporated, the reaction
mixture was chromatographed on silica gel with 8:1
hexanes:THF. The product was further purified by size
exclusion column chromatography (BioRad Bio-Beads
SX-1 packed in THF, gravity flow). Yield 42.2 mg (14%
based on 0.154 g of N,N-dihexylamino-4-vinylbenzene).
1H NMR (300 MHz; CDCl3): d, ppm 8.04 (d, 1H, J = 7.6
Hz, Ph-H), 7.84 (d, 1H, J = 16.4 Hz, vinyl-H), 7.50 (d,
2H, J = 8.8 Hz, Ph-H), 7.38 (d, 1H, J = 16.2 Hz, vinyl-H),
7.37 (d, 1H, J = 7.8 Hz, Ph-H), 6.64 (d, 2H, J = 8.9 Hz,
Ph-H), 3.30 (t, 4H, J = 7.6 Hz, –NCH2–), 1.61 (m, 4H,
1
thiadiazole). H NMR (300 MHz; 1 drop pyridine-d5 in
CDCl3): d, ppm 9.92 (d, 4H, J = 4.6 Hz, b-H), 8.89 (d,
4H, J = 4.5 Hz, b-H), 8.21 (d, 2H, J = 7.4 Hz, Ph-H), 8.13
(d, 2H, J = 7.4 Hz, Ph-H), 8.09 (d, 2H, J = 7.4 Hz, Ph-H),
7.98 (d, 4H, J = 8.7 Hz, Ph-H), 7.75 (d, 2H, J = 7.3 Hz,
Ph-H), 7.73 (t, 2H, J = 8.3 Hz, Ph-H), 7.09 (d, 4H, J =
8.8 Hz, Ph-H), 7.04 (d, 4H, J = 8.5 Hz, Ph-H), 4.06 (t,
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 6–14

DESIGN OF DIETHYNYL PORPHYRIN DERIVATIVES WITH HIGH NEAR INFRARED FLUORESCENCE QUANTUM YIELDS
7
–NC–CH2–), 1.15–1.45 (m, 12H, –CH2–), 0.91 (t, 6H,
J = 6.7 Hz, –CH3). MS (CI): m/z 547.1481 (calcd. for
[M]+ 547.148).
facile through the agency of palladium-catalyzed cross-
coupling reactions. In 2–9, each aromatic unit is linked
by either ethyne or ethene units through Sonogashira or
Heck coupling reactions. The 10- and 20-meso-positions
of the (porphinato)zinc cores of 1–9 feature either
3,5-bis(9′-methoxy-1′,4′,7′-trioxanonyl)phenyl (1) or
2,6-bis(3′,3′-dimethyl-1′-butyloxy)phenyl substituents
(2–9) to ensure high solubility. Fluorophores 2–9 were
synthesized by Pd-mediated cross-coupling reactions
involving appropriately modified terminal substituents
and 5,15-dibromo- or 5,15-diethynyl(porphinato)zinc(II)
synthons (Experimental Section).
(5,15-Bis([7′-(4′′-N,N-dihexylaminophenylethenyl)
benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-
bis[2′,6′-bis(3′′,3′′-dimethyl-1′′-butyloxy)phenyl]
porphinato)zinc(II) (9). 4-(4′-N,N-Dihexylamino-
phenylethenyl)-7-iodobenzo[c][1,2,5]thiadiazole
(42.2 mg, 7.71 × 10-5 mol), 5,15-diethynyl-10,20-bis[2′,-
6′-bis(3′′,3′′-dimethyl-1′′-butyloxy)phenyl]porphinato)
zinc(II) (38.0 mg, 3.90 × 10-5 mol), Pd(PPh3)4 (10.5 mg,
9.1 × 10-6 mol), CuI (1.0 mg, 5.3 × 10-6 mol), and dry THF
(5.0 mL) were added to a 100-mL round-bottom flask. Ar
was bubbled into the reaction mixture for 5 min before
piperidine (0.50 mL) was added. The reaction mixture
was stirred at 47°C for 43 h under Ar. After cooling, the
solventwasevaporated.Theresiduewaschromatographed
on silica gel with 5:1 hexanes:THF as the eluent. The
product was further purified by size exclusion column
chromatography (BioRad Bio-Beads SX-1 packed
in THF, gravity flow). Yield 30.4 mg (43% based on
42.2 mg of 4-(4′-N,N-dihexylaminophenylethenyl)-7-
Steady-state electronic absorption spectra
Electronic absorption spectra of NIR fluorophores
2–9 recorded in THF solvent are displayed in Fig. 2.
These chromophores feature lowest energy Q absorption
bands that are significantly red-shifted (1985–3070 cm-1)
and intensified (~20 to 50-fold enhanced in oscillator
strength) relative to the analogous transition manifold of
[5,10,15,20-tetraphenyl(porphinato)]zinc(II) (TPPZn)
[100]. While chromophores 2 and 3 manifest spectral
signatures akin to other closely related, [5,15-bis[(aryl)
ethynyl]-10,20-diphenylporphinato]zinc(II) complexes
[42], note that structures 4–9, which incorporate benzo[c]
[1,2,5]thiadiazole units, manifest spectra that bear
distinct similarities to chlorophylls and structurally
related molecules [103]. The extinction coefficients
of the x-polarized Q-band [Qx(0,0)] transitions for 4–9
are significantly enhanced relative to 2 and 3, which
bear 5,15-bis(arylethynyl) macrocycle substituents
(Fig. 2, Table 1). As conjugation is expanded at the
porphyrin (5,15-bis(benzo[c][1′,2′,5′]thiadiazol-4′-
ylethynyl) moieties [4→5→(6, 7, 8, 9)] (Fig. 2, Table 1),
increasingly pronounced B-state (Soret) transition
manifold splitting is evident; note that the Qx(0,0)
transition extinction coefficients for fluorophores 6–9
surpass those of their most intense respective B-band
absorption, and exceed 105 M-1.cm-1, a value comparable
to Q-state absorptions characteristic of chlorophylls and
phthalocyanines [30, 37]. In contrast to the full widths at
half maximum (FWHM) values for the B-band manifolds
of 6–9, which span 4430–6480 cm-1 and greatly exceed
that of the TPPZn benchmark (660 cm-1), the FWHMs
of their respective Qx(0,0) transitions range from 812 to
940 cm-1. Compounds 3 and 8 highlight the qualitative
impact of 5,15-bis(benzo[c][1′,2′,5′]thiadiazol-4′-
ylethynyl) substituents relative to corresponding 5,15-
bis[(aryl)ethynyl] groups upon the (porphinato)zinc
chromophore long-wavelength absorption maximum:
note the x-polarized Q-state absorption maximum
for 8 is 928 cm-1 red-shifted relative to that for 3. The
enhanced p–conjugation afforded by the benzo[c][1,2,5]
thiadiazolyl group is consistent with its proquinoidal
character [104], and earlier work which establishes that
meso (benzo[c][1,2,5]thiadiazol-4-ylethynyl) substituents
1
iodobenzo[c][1,2,5]thiadiazole). H NMR (500 MHz; 1
drop pyridine-d5 in CDCl3): d, ppm 9.90 (d, 4H, J = 4.5
Hz, b-H), 8.84 (d, 4H, J = 4.5 Hz, b-H), 8.14 (d, 2H,
J = 7.2 Hz, Ph-H), 7.99 (d, 2H, J = 16.1 Hz, vinyl-H),
7.77 (d, 2H, J = 7.4 Hz, Ph-H), 7.71 (t, 2H, J = 8.5 Hz,
Ph-H), 7.57 (d, 4H, J = 8.4 Hz, Ph-H), 7.55 (d, 2H,
J = 16.0 Hz, vinyl-H), 7.02 (d, 4H, J = 8.6 Hz, Ph-H),
6.68 (d, 4H, J = 8.7 Hz, Ph-H), 3.92 (t, 8H, J = 7.4 Hz,
–O–CH2–C), 3.33 (t, 8H, J = 7.6 Hz, –N–CH2–C), 1.63
(m, 8H, –CH2–), 1.3–1.4 (m, 24H, –CH2–), 0.93 (t, 12H,
J = 6.7 Hz, –CH3), 0.84 (t, 8H, J = 7.5 Hz, –O–C–CH2–),
0.39 (s, 36H, –C–CH3). MS (MALDI-TOF): m/z 1811.0
(calcd. for [M]+ 1810.932).
RESULTS AND DISCUSSION
Synthesis
Chromophores 2–9 are based on a (5,15-diethy-
nylporphinato)zinc(II) framework and feature symmetric
donor or acceptor units appended at the meso-ethynyl
positions that derive from phenylene and benzo[c]
[1,2,5]thiadiazole building blocks; these structures,
along with the TMS-protected (5,15-diethynyl-10,20-
bis[3′,5′-bis(9′′-methoxy-1′′,4′′,7′′-trioxanonyl)phenyl]
porphinato)zinc(II) reference monomer (1), are shown in
Fig. 1. Scheme 1 details the syntheses of fluorophores 3–9.
The proquinoidal spacer unit, benzo[c][1,2,5]thiadiazole,
which extends p-conjugation from the porphyrin core for
4–9, has been used not only as a common building block
to enhance electronic delocalization within p-conjugated
oligomers and polymers, but also as an electron accepting
moiety[55,99,101,102].Incorporationofbenzo[c][1,2,5]
thiadiazole into conjugated organic networks is made
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 7–14

8
K. SUSUMU AND M. J. THERIEN
Scheme 1. Synthetic routes to 5,15-diethynyl-(porphinato)zinc(II)-based fluorophores 3–9 and to key precursor compounds
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 8–14

DESIGN OF DIETHYNYL PORPHYRIN DERIVATIVES WITH HIGH NEAR INFRARED FLUORESCENCE QUANTUM YIELDS
9
Fig. 2. Absorption (black line) and fluorescence (red line) spectra of 5,15-diethynyl-(porphinato)zinc(II)-based fluorophores 2–9
recorded in THF solvent
drive pronounced S1 state cumulenic character for
(porphinato)zinc-based chromophores [55].
degrees of conjugation [4→5→(6, 7, 8, 9)] (Fig. 2,
Table 1); note in this regard that fluorophore 7 features
an emission band maximum centered at 748 nm, and
that structures 2–9 feature narrow fluorescence bands
(620 cm-1 < FWHM(S1→S0) < 1130 cm-1) that are
significantly reduced with respect to the S1→S0 FWHM
value determined for TPPZn (1924 cm-1). Note also
that the narrow fluorescence bands of 2–9 resemble the
spectral breadths of their respective lowest energy Q-state
absorptionmanifolds(Table1)andfeaturelow-magnitude
Fluorescence spectra
Figure 2 also highlights the fluorescence spectra
recorded for chromophores 2–9 in THF solvent; these
spectra mirror the respective lowest energy Q-state
absorption manifolds for these chromophores. The
fluorescence energy maxima red-shift with increasing
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 9–14

10
K. SUSUMU AND M. J. THERIEN
Table 1. Comparative electronic absorption and steady-state fluorescence spectral data determined for chromophores 1–9 in THF
solvent relative to the TPPZn benchmark
l
max (S0→S1),
e
max (S0→S1),
FWHM
lmax
(S1→S0), nm
FWHM
Stokes shift,
cm-1c
nma
M-1.cm-1a
(S0→S1), cm-1a
(S1→S0), cm-1
TPPZn (in benzene)
589
632
669
667
674
701
704
715
711
719
3680
33,200
577
438
824
704
654
737
812
939
818
940
605
638
678
674
687
710
730
748
735
743
1924b
626
656
618
809
649
922
1131
890
870
449
149
198
156
281
181
506
617
459
449
1
2
3
4
5
6
7
8
9
57,000
94,000
84,000
108,000
127,000
109,400
134,000
105,000
a For 1–9, the value reported corresponds to that for the x-polarized (S0→S1) absorption. Note that for the TPPZn chromophore, the
value reported corresponds to that for the Q(0,0) transition. b The value reported corresponds to that for the Q-state manifold. c The
difference in energy between the absorption (S0→S1) and fluorescence (S1→S0) band maxima.
Table 2. Comparative x-polarized [S0→S1; Qx(0,0)] integrated absorptive oscillator strengths, fluorescence quantum yields,
fluorescence lifetimes, experimental and calculated radiative rate constants, and experimental non-radiative rate constants determined
for chromophores 1–9 in THF solvent relative to the TPPZn benchmark
Oscillator
strengtha
Ffb
tf, ns
kr (× 107 s-1)
knr (× 107 s-1)
kr(calc)d (× 107 s–1)
TPPZn (in benzene)
0.00977
0.0669
0.216
0.304
0.253
0.366
0.474
0.473
0.504
0.454
0.033c
2.09
1.99
2.04
1.63
1.42
1.20
1.97
1.87
1.71
1.37
1.58
2.91
46.27
47.34
38.24
46.01
59.86
67.50
34.52
34.76
37.43
54.01
1.78
4.30
7.72
11.1
9.23
11.3
13.0
11.8
13.8
11.5
1
2
3
4
5
6
7
8
9
0.058 (0.021)
0.22 (0.044)
0.25 (0.043)
0.15 (0.013)
0.19 (0.012)
0.32 (0.020)
0.35 (0.035)
0.36 (0.032)
0.26 (0.029)
10.78
15.34
10.56
15.83
16.24
18.72
21.05
18.98
a f = 4.6 × 10-9∙emax∙Dν1/2; the oscillator strengths were calculated for the x-polarized (S0→S1) absorption. Note that for the TPPZn
b
chromophore, the reported integrated oscillator strength corresponds to that for the Q-state transition manifold. Fluorescence
quantum yields determined relative to free base TPP in benzene (Ff = 0.13); parenthetical values represent standard deviations from
the mean. c From Ref. 100. d Calculated using Equation 2.
Stokes shifts (155–620 cm-1), congruent with a minimal
degree of excited-state structural relaxation relative the
ground-state conformation for these chromophores.
Ff < 0.36; Table 2). Further, given the shape and
intensity of the steady-state fluorescence spectra of
these monomeric (porphinato)zinc chromophores that
bear either 5,15-bis[(aryl)ethynyl] or 5,15-bis(benzo[c]
[1′,2′,5′]thiadiazol-4′-ylethynyl) substituents, coupled
with the fact that the emission band maxima of these
species are significantly red-shifted (1690–3160 cm-1)
with respect to the TPPZn benchmark (Table 1), suggest
an analysis of the S1 state photophysics within the context
of the Strickler–Berg model, which relates increases in
Strickler–Berg analysis of the S1-state
photophysics of fluorophores 2–9
Relative to the (porphinato)zinc chromophore
TPPZn (Ff = 0.033), the fluorescence quantum yields
of fluorophores 2–9 are particularly dramatic (0.15 <
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 10–14

DESIGN OF DIETHYNYL PORPHYRIN DERIVATIVES WITH HIGH NEAR INFRARED FLUORESCENCE QUANTUM YIELDS
11
the integrated oscillator strength of the lowest-energy
ground-state absorption band with a corresponding
augmentation of the radiative decay rate constant (kr,
Equation 2) [22].
rate constants, and non-radiative rate constants of fluoro-
phores 1–9 relative to the TPPZn benchmark. Note the
distinct increase in the magnitude of the radiative rate
constant with increasing x-polarized Q-state oscillator
strength (Fig. 3B), and that the measured kr values for
fluorophores 5–9 exceed that of the TPPZn by more
than an order of magnitude. This apparent Stricker–
Berg dependence of the radiative rate constant upon the
integrated lowest energy S0→S1 oscillator strength gives
rise to a family of porphyrin-based NIR fluorophores in
which the longest wavelength emitter (7, 748 nm) features a
fluorescence quantum yield (Ff = 0.35; Tables 1 and 2) that
exceeds that of chromophores 1–6 and 9, which emit to the
blue of this wavelength.
As emission wavelengths approach the NIR spectral
domain, the simple Stricker–Berg predicted dependence
of the radiative rate constant upon the magnitude of the
integrated oscillator strength is generally mitigated by
expected energy gap law effects [23], where increasing
magnitudes of the S0–S1 internal conversion rate constant
(kic) track with diminishing S0–S1 energy gaps and thus
sharply decrease Ff. In these chromophores, two factors
conspire to enhance Ff as emission wavelength increases
over the 650–750 nm spectral domain. The first of these
derives from the fact that the proquinoidal benzo[c]
[1,2,5]thiadiazole unit minimizes the extent of excited-
state structural relaxation relative the ground-state
conformation [55] for chromophores 4–9, reflected by
the narrow fluorescence bands and modest Stokes shifts
determined for these species (Fig. 2; Tables 1 and 2), and
thereby reduces S1–S0 Franck–Condon overlap important
for determining the magnitude of kic. The second factor
that drives this unusual dependence of Ff upon emission
wavelength stems from the fact that for these ethyne-
elaborated (porphinato)zinc derivatives, intersystem
-1
gl
ꢀ-3
kr = 2.880 ×10-9 n2 ν f
ꢀ
ed ln ν
(2)
∫
Av
gu
Here kr is radiative decay rate constant, n is the
refractive index of the solvent, gl and gu are the respective
degeneracies of the ground and excited states, e is the
molar extinction coefficient, ν is the frequency of the
~
-1
transition in cm-1. The term 〈νf-3〉 is expressed as;
Av
I(ν)dν
ν-3I(ν)dν
-1
∫
ꢀ-3
νf
=
(3)
Av
∫
where I is the intensity of the fluorescence spectrum,
measured in terms of relative numbers of quanta at each
frequency. The fluorescence quantum yield (Ff) is simply
described by Equation 4;
kr
Ff =
(4)
kr + knr
where knr describes the magnitude of the non-radiative
decay rate constant, which corresponds to the sum of the
internal conversion (kic) and intersystem crossing (kisc)
rate constants. Provided that the magnitudes of the non-
radiative rate remain approximately constant within a
family of closely related chromophores, an increase in the
integrated oscillator strength results in a corresponding
increase in the fluorescence quantum yield.
Figure 3 highlights the x-polarized Q-state oscillator
strength dependent fluorescence quantum yields, radiative
Fig. 3. x-Polarized Q-state [Qx (S0→S1)] oscillator strength dependent fluorescence quantum yields, radiative rate constants (kr),
and non-radiative rate constants (knr) of diethynyl(porphinato)zinc(II) derivatives (1–9) relative to the [5,10,15,20-tetraphenyl-
(porphinato)]zinc(II) (TPPZn) benchmark. (a) x-Polarized Q-state oscillator strength dependence of the fluorescence quantum
yield. (b) x-Polarized Q-state oscillator strength dependence of the radiative and non-radiative decay rate constant magnitudes
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 11–14

12
K. SUSUMU AND M. J. THERIEN
crossing into the triplet manifold generates T1 states that
manifest more spatially confined excitations relative to
the globally delocalized S1 states of these chromophores
[41, 45, 47, 54, 62]. This diminished overlap of S1 and
T1 state wavefunctions mitigates S1-T1 intersystem
crossing rate constants (kisc values), and thus serves to
counter-balance the effect of augmented Franck–Condon
mediated internal conversion that typically accompanies
S0-S1 energy gap reductions; this effect has been detailed
previously for closely related compounds [57]. Thus,
for 4–9, extension of x-polarized conjugation of the
(5,15-diethynylporphinato)zinc(II) framework via the
benzo[c][1,2,5]thiadiazole moiety causes the magnitude
of kr to increase faster than does the magnitude of knr as
emission wavelength increases, providing substantial
fluorescence quantum yields that manifest a weak energy
gap law [23] dependence over this spectral regime.
emissive NIR fluorophores that derive from a monomeric
(5,15-diethynyl-porphinato)zinc framework.
Acknowledgements
This work was supported through the Department
of Defense (W81XWH-13-1-0086). The authors thank
ProfessorFelixN. CastellanoandDr. RadiyIslangulovfor
their assistance with fluorescence lifetime measurements.
REFERENCES
1. Weissleder R. Nat. Biotechnol. 2001; 19: 316–317.
2. Weissleder R and Ntziachristos V. Nat. Med. 2003;
9: 123–128.
3. Bremer C, Ntziachristos V and Weissleder R. Eur.
Radiol. 2003; 13: 231–243.
4. Frangioni JV. Curr. Opin. Chem. Biol. 2003; 7:
626–634.
5. Hilderbrand SA and Weissleder R. Curr. Opin.
Chem. Biol. 2010; 14: 71–79.
CONCLUSION
We describe a design strategy for (porphinato)zinc-
based chromophores that possess large NIR fluorescence
quantum yields. These fluorophores are based on a (5,15-
diethynylporphinato)zinc(II) framework and feature
symmetric donor or acceptor units appended at the
meso-ethynyl positions via benzo[c][1,2,5]thiadiazole
moieties. These chromophores possess red-shifted
absorption and emission bands relative to TPPZn and
6. Martínez-Díaz MV, de la Torre G and Torres T.
Chem. Commun. 2010; 46: 7090–7108.
7. Liu Y, Lin H, Dy JT, Tamaki K, Nakazaki J,
Nakayama D, Uchida S, Kubo T and Segawa H.
Chem. Commun. 2011; 47: 4010–4012.
8. Chang Y-C, Wang C-L, Pan T-Y, Hong S-H, Lan
C-M, Kuo H-H, Lo C-F, Hsu H-Y, Lin C-Y and Diau
EW-G. Chem. Commun. 2011; 47: 8910–8912.
9. Mathew S, Yella A, Gao P, Humphry-Baker R,
Curchod BFE, Ashari-Astani N, Tavernelli I,
Rothlisberger U, Nazeeruddin MK and Grätzel M.
Nature Chem. 2014; 6: 242–247.
(5,15-diethynyl-10,20-arylporphinato)zinc(II)
bench-
marks that range between 650 and 750 nm and bear
distinct spectral similarities to those manifest by
chlorophylls and structurally related molecules.
Interestingly, the measured radiative decay rate
constants for these emitters track with the integrated
oscillator strengths of their respective x-polarized
Q-band absorptions, and thus define an unusual family
of high quantum yield NIR fluorophores in which
emission intensity is governed by a simple Strickler–
Berg dependence. These photophysical properties
derive from the facts that: (i) the proquinoidal benzo[c]
[1,2,5]thiadiazole unit minimizes the extent of excited-
state structural relaxation relative the ground-state
conformation [55], and (ii) meso-ethynyl elaborated
(porphinato)zinc compounds are characterized by T1
states that are more spatially confined than their globally
delocalized S1 states [41, 45, 47, 54, 62], which result
in diminished S1-T1 intersystem crossing rate constants
relative to conventional (porphinato)zinc chromophores.
For these NIR fluorophores, these effects cause the
magnitude of kr to increase faster than does the magnitude
of knr as emission wavelength increases, providing
substantial fluorescence quantum yields that manifest a
weak energy gap law [23] dependence over the spectral
regime (685–750 nm) spanned by these emitters. These
designs that take advantage of these photophysical
properties make possible broadly absorptive and strongly
10. D’Souza F, Amin AN, El-Khouly ME, Subbaiyan
NK, Zandler ME and Fukuzumi S. J. Am. Chem.
Soc. 2012; 134: 654–664.
11. Balzani V, Credi A and Venturi M. ChemSusChem
2008; 1: 26–58.
12. Roncali J. Chem. Rev. 1997; 97: 173–205.
13. van Mullekom HAM, Vekemans JAJM, Havinga EE
and Meijer EW. Mater. Sci. Eng. 2001; 32: 1–40.
14. Tsuda A and Osuka A. Science 2001; 293: 79–82.
15. Kiyose K, Kojima H and Nagano T. Chem. Asian J.
2008; 3: 506–515.
16. Escobedo JO, Rusin O, Lim S and Strongin RM.
Curr. Opin. Chem. Biol. 2010; 14: 64–70.
17. Qian G and Wang ZY. Chem. Asian J. 2010; 5:
1006–1029.
18. Luo S, Zhang E, Su Y, Cheng T and Shi C.
Biomaterials 2011; 32: 7127–7138.
19. Mori H, Tanaka T and Osuka A. J. Mater. Chem. C
2013; 1: 2500–2519.
20. Zhao W and Carreira EM. Angew. Chem. Int. Ed.
2005; 44: 1677–1679.
21. Umezawa K, Nakamura Y, Makino H, Citterio
D and Suzuki K. J. Am. Chem. Soc. 2008; 130:
1550–1551.
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 12–14

DESIGN OF DIETHYNYL PORPHYRIN DERIVATIVES WITH HIGH NEAR INFRARED FLUORESCENCE QUANTUM YIELDS
13
22. Strickler SJ and Berg RA. J. Chem. Phys. 1962; 37:
814–822.
23. Englman R and Jortner J. Mol. Phys. 1970; 18:
145–164.
24. Gouterman M. J. Mol. Spectrosc. 1961; 6: 138–163.
25. Finikova OS, Cheprakov AV and Vinogradov SA.
J. Org. Chem. 2005; 70: 9562–9572.
47. Angiolillo PJ, Susumu K, Uyeda HT, Lin VS-Y,
Shediac R and Therien MJ. Synth. Met. 2001; 116:
247–253.
48. Fletcher JT and Therien MJ. Inorg. Chem. 2002; 41:
331–341.
49. Fletcher JT and Therien MJ. J. Am. Chem. Soc.
2002; 124: 4298–4311.
26. Nakamura J, Okujima T, TomimoriY, Komobuchi N,
Yamada H, Uno H and Ono N. Heterocycles 2010;
80: 1165–1175.
27. Davis NKS, Thompson AL and Anderson HL. Org.
Lett. 2010; 12: 2124–2127.
28. Davis NKS, Thompson AL and Anderson HL.
J. Am. Chem. Soc. 2011; 133: 30–31.
29. Diev VV, Schlenker CW, Hanson K, Zhong Q,
Zimmerman JD, Forrest SR and Thompson ME.
J. Org. Chem. 2012; 77: 143–159.
50. Susumu K and Therien MJ. J. Am. Chem. Soc. 2002;
124: 8550–8552.
51. Rubtsov IV, Susumu K, Rubtsov GI and Therien
MJ. J. Am. Chem. Soc. 2003; 125: 2687–2696.
52. Redmore NP, Rubtsov IV and Therien MJ. J. Am.
Chem. Soc. 2003; 125: 8769–8778.
53. Rubtsov IV, Redmore NP, Hochstrasser RM and
TherienMJ. J.Am. Chem. Soc. 2004;126:2684–2685.
54. Angiolillo PJ, Uyeda HT, Duncan TV and Therien
MJ. J. Phys. Chem. B 2004; 108: 11893–11903.
55. Susumu K, Duncan TV and Therien MJ. J. Am.
Chem. Soc. 2005; 127: 5186–5195.
30. Sauer K, Smith JRL and Schultz AJ. J. Am. Chem.
Soc. 1966; 88: 2681–2688.
31. Connolly JS, Samuel EB and Janzen AF. Photo-
chem. Photobiol. 1982; 36: 565–574.
32. Forster LS and Livingston R. J. Chem. Phys. 1952;
20: 1315–1320.
33. Kee HL, Kirmaier C, Tang Q, Diers JR, Muthiah
C, Taniguchi M, Laha JK, Ptaszek M, Lindsey JS,
Bocian DF and Holten D. Photochem. Photobiol.
2007; 83: 1110–1124.
34. Taniguchi M, Cramer DL, Bhise AD, Kee HL,
Bocian DF, Holten D and Lindsey JS. New J. Chem.
2008; 32: 947–958.
35. KozyrevA, EthirajanM, ChenP, OhkuboK, Robinson
BC, Barkigia KM, Fukuzumi S, Kadish KM and
Pandey RK. J. Org. Chem. 2012; 77: 10260–10271.
36. Seybold PG and Gouterman M. J. Mol. Spectrosc.
1969; 31: 1–13.
37. Kobayashi N, Ogata H, Nonaka N and Luk’yanets
EA. Chem. Eur. J. 2003; 9: 5123–5134.
38. Susumu K, Maruyama H, Kobayashi H and
Tanaka K. J. Mater. Chem. 2001; 11: 2262–2270.
39. Lin VS-Y, DiMagno SG and Therien MJ. Science
1994; 264: 1105–1111.
56. Susumu K, Frail PR, Angiolillo PJ and Therien MJ.
J. Am. Chem. Soc. 2006; 128: 8380–8381.
57. Duncan TV, Susumu K, Sinks LE and Therien MJ.
J. Am. Chem. Soc. 2006; 128: 9000–9001.
58. Duncan TV, Wu SP and Therien MJ. J. Am. Chem.
Soc. 2006; 128: 10423–10435.
59. Frail PR, Susumu K, Huynh M, Fong J, Kikkawa JM
and Therien MJ. Chem. Mater. 2007; 19: 6062–6064.
60. Duncan TV, Ishizuka T and Therien MJ. J. Am.
Chem. Soc. 2007; 129: 9691–9703.
61. Duncan TV, Frail PR, Miloradovic IR and Therien
MJ. J. Phys. Chem. B 2010; 114: 14696–14702.
62. Angiolillo PJ, Rawson J, Frail PR and Therien MJ.
Chem. Commun. 2013; 49: 9722–9724.
63. LeCours SM, Guan H-W, DiMagno SG, Wang CH
and Therien MJ. J. Am. Chem. Soc. 1996; 118:
1497–1503.
64. Priyadarshy S, Therien MJ and Beratan DN. J. Am.
Chem. Soc. 1996; 118: 1504–1510.
65. Karki L, Vance FW, Hupp JT, LeCours SM
and Therien MJ. J. Am. Chem. Soc. 1998; 120:
2606–2611.
40. Lin VS-Y and Therien MJ. Chem. Eur. J. 1995; 1:
645–651.
41. Angiolillo PJ, LinVS-Y,Vanderkooi JM andTherien
MJ. J. Am. Chem. Soc. 1995; 117: 12514–12527.
42. LeCours SM, DiMagno SG and Therien MJ. J. Am.
Chem. Soc. 1996; 118: 11854–11864.
43. LeCours SM, Philips CM, de Paula JC and Therien
MJ. J. Am. Chem. Soc. 1997; 119: 12578–12589.
44. Kumble R, Palese S, Lin VS-Y, Therien MJ and
Hochstrasser RM. J. Am. Chem. Soc. 1998; 120:
11489–11498.
66. Uyeda HT, Zhao Y, Wostyn K, Asselberghs I, Clays
K, Persoons A and Therien MJ. J. Am. Chem. Soc.
2002; 124: 13806–13813.
67. Duncan TV, Rubtsov IV, Uyeda HT and Therien
MJ. J. Am. Chem. Soc. 2004; 126: 9474–9475.
68. Zhang T-G, Zhao Y, Asselberghs I, Persoons A,
Clays K and Therien MJ. J. Am. Chem. Soc. 2005;
127: 9710–9720.
69. Zhang T-G, ZhaoY, Song K,Asselberghs I, Persoons
A, Clays K and Therien MJ. Inorg. Chem. 2006; 45:
9703–9712.
45. Shediac R, Gray MHB, Uyeda HT, Johnson RC,
Hupp JT, Angiolillo PJ and Therien MJ. J. Am.
Chem. Soc. 2000; 122: 7017–7033.
46. Fletcher JT and Therien MJ. J. Am. Chem. Soc.
2000; 122: 12393–12394.
70. Xu T, Wu SP, Miloradovic I, Therien MJ and Blasie
JK. Nano Lett. 2006; 6: 2387–2394.
71. DuncanTV, SongK, HungS-T, MiloradovicI, Nayak
A, Persoons A, Verbiest T, Therien MJ and Clays K.
Angew. Chem. Int. Ed. 2008; 47: 2978–2981.
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 13–14

14
K. SUSUMU AND M. J. THERIEN
72. Keinan S, Therien MJ, Beratan DN and Yang W.
J. Phys. Chem. A 2008; 112: 12203–12207.
73. Therien MJ. Nature 2009; 458: 716–717.
74. Hu X, Xiao D, Keinan S, Asselberghs I, Therien
MJ, Clays K, Yang W and Beratan DN. J. Phys.
Chem. C 2010; 114: 2349–2359.
75. Gonella G, Dai H-L, Fry HC, Therien MJ, Krishnan
V, Tronin A and Blasie JK. J. Am. Chem. Soc. 2010;
132: 9693–9700.
76. Krishnan V, Tronin A, Strzalka J, Fry HC, Therien
MJ and Blasie JK. J. Am. Chem. Soc. 2010; 132:
11083–11092.
77. Singh-Rachford TN, Nayak A, Muro-Small ML,
Goeb S, Therien MJ and Castellano FN. J. Am.
Chem. Soc. 2010; 132: 14203–14211.
and Therien MJ. Proc. Natl. Acad. Sci. USA 2005;
102: 2922–2927.
89. Ghoroghchian PP, Frail PR, Susumu K, Park T-H,
Wu SP, Uyeda HT, Hammer DA and Therien MJ.
J. Am. Chem. Soc. 2005; 127: 15388–15390.
90. Wu SP, Lee I, Ghoroghchian PP, Frail PR, Zheng G,
Glickson JD and Therien MJ. Bioconjugate Chem.
2005; 16: 542–550.
91. Ghoroghchian PP, Lin JJ, Brannan AK, Frail PR,
Bates FS, Therien MJ and Hammer DA. Soft Matter
2006; 2: 973–980.
92. Ghoroghchian PP, Frail PR, Li G, Zupancich JA,
Bates FS, Hammer DA and Therien MJ. Chem.
Mater. 2007; 19: 1309–1318.
93. Christian NA, Milone MC, Ranka SS, Li G, Frail
PR, Davis KP, Bates FS, Therien MJ, Ghorogh-
chian PP, June CH and Hammer DA. Bioconjugate
Chem. 2007; 18: 31–40.
78. Ishizuka T, Sinks LE, Song K, Hung S-T, Nayak A,
Clays K and Therien MJ. J. Am. Chem. Soc. 2011;
133: 2884–2896.
79. Jiang N, Zuber G, Keinan S, Nayak A, Yang W,
Therien MJ and Beratan DN. J. Phys. Chem. C
2012; 116: 9724–9733.
94. Duncan TV, Ghoroghchian PP, Rubtsov IV, Hammer
DA and Therien MJ. J. Am. Chem. Soc. 2008; 130:
9773–9784.
80. Fry HC, Lehmann A, Sinks LE, Asselberghs I, Tro-
nin A, Krishnan V, Blasie JK, Clays K, DeGrado
WF, Saven JG and Therien MJ. J. Am. Chem. Soc.
2013; 135: 13914–13926.
81. Deria P, Bargen CDV, Olivier J-H, Kumbhar AS,
Saven JG and Therien MJ. J. Am. Chem. Soc. 2013;
135: 16220–16234.
82. OstrowskiJC, SusumuK, RobinsonMR,TherienMJ
and Bazan GC. Adv. Mater. 2003; 15: 1296–1300.
83. Banerjee P, Conklin D, Nanayakkara S, Park T-H,
Therien MJ and Bonnell DA. ACS Nano 2010; 4:
1019–1025.
84. Conklin D, Park T-H, Nanayakkara S, Therien MJ
and Bonnell DA. Adv. Funct. Mater. 2011; 21:
4712–4718.
95. Ghoroghchian PP, Therien MJ and Hammer DA.
Wiley Interdiscip. Rev.: Nanomed. Nanobiotechnol.
2009; 1: 156–167.
96. Christian NA, Benencia F, Milone MC, Li G, Frail
PR, Therien MJ, Coukos G and Hammer DA. Mol.
Imaging Biol. 2009; 11: 167–177.
97. Kamat NP, Liao Z, Moses LE, Rawson J, Therien
MJ, Dmochowski IJ and Hammer DA. Proc. Natl.
Acad. Sci. U.S.A. 2011; 108: 13984–13989.
98. Pilgram K, Zupan M and Skiles R. J. Heterocycl.
Chem. 1970; 7: 629–633.
99. Susumu K, Fisher JAN, Zheng J, Beratan DN,Yodh
AG and Therien MJ. J. Phys. Chem. A 2011; 115:
5525–5539.
100. Quimby DJ and Longo FR. J. Am. Chem. Soc. 1975;
97: 5111–5117.
101. Velusamy M, Justin Thomas KR, Lin JT, Hsu Y-C
and Ho K-C. Org. Lett. 2005; 7: 1899–1902.
102. Bundgaard E and Krebs FC. Sol. Energy Mater. Sol.
Cells 2007; 91: 954–985.
85. Conklin D, Nanayakkara S, Park T-H, Lagadec MF,
Stecher JT, Therien MJ and Bonnell DA. Nano Lett.
2012; 12: 2414–2419.
86. Li Z, Park T-H, Rawson J, Therien MJ and Borguet
E. Nano Lett. 2012; 12: 2722–2727.
87. Conklin D, Nanayakkara S, Park T-H, Lagadec MF,
Stecher JT, Chen X, Therien MJ and Bonnell DA.
ACS Nano 2013; 7: 4479–4486.
88. Ghoroghchian PP, Frail PR, Susumu K, Blessington
D, Brannan AK, Bates FS, Chance B, Hammer DA
103. Linnanto J and Korppi-Tommola J. J. Phys. Chem.
A 2001; 105: 3855–3866.
104. Neto BAD, Lapis AAM, Júnior ENdS and Dupont J.
Eur. J. Org. Chem. 2013: 228–255.
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 14–14