A R T I C L E S
Harriman et al.
[M + H]+, 100. Anal. Calcd for C62H47BN2‚1/2CH2Cl2 (Mr ) 830.86
+ 42.46): C, 85.96; H, 5.54; N, 3.21. Found: C, 85.42; H, 5.51; N,
3.21.
beam was combined with the excitation pulse and used as the diagnostic
beam. The two beams were directed to different parts of the entrance
slit of a cooled charge-coupled device (CCD) detector and used to
calculate differential absorbance values. The CCD shutter was kept open
for 1 s, and the accumulated spectra were averaged. This procedure
was repeated until about 100 individual spectra had been averaged.
Time-resolved spectra were recorded with a delay line stepped in
increments of 100 fs. The sample, possessing an absorbance of ca. 1 at
420 nm, was flowed through a quartz cuvette (optical path length ) 2
mm) and maintained under an atmosphere of N2.
Electrochemical studies employed cyclic voltammetry with a con-
ventional three-electrode system using a BAS CV-50W voltammetric
analyzer equipped with a Pt microdisk (2 mm2) working electrode and
a platinum wire counter electrode. Ferrocene was used as an internal
standard and was calibrated against a saturated calomel reference
electrode (SCE) separated from the electrolysis cell by a glass frit
presoaked with electrolyte solution. Solutions contained the electrode-
active substrate (ca. 1.5 × 10-3 M) in solvent previously deoxygenated
with anhydrous nitrogen and with tetra-n-butylammonium hexafluo-
rophosphate (0.1 M) as supporting electrolyte. The quoted half-wave
potentials were reproducible to within (15 mV.
4-(Pyrenyl-1-ethynyl)-4′-(perylen-3-ethynyl)-1,3,5,7,8-pentamethyl-
2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3). Isolated yield: 28%,
1
3
0.149 g. H NMR (CDCl3): δ ) 8.64 (d, 1H, J ) 9.0 Hz), 8.34 (d,
1H, 3J ) 8.0 Hz), 8.24 (t, 1H, 3J ) 8.0 Hz), 8.20-8.02 (m, 10H), 7.85
(d, 1H, J ) 9.0 Hz), 7.62 (t, 1H, J ) 8.0 Hz), 7.55-7.48 (m, 5H),
3.05 (s, 3H), 3.01 (s, 3H), 2.80 (s, 3H), 2.60 (q, 2H, 3J ) 7.4 Hz), 2.57
3
3
3
3
(q, 2H, J ) 7.4 Hz), 2.51 (s, 3H), 2.49 (s, 3H), 1.19 (t, 3H, J ) 7.4
Hz), 1.16 (t, 3H, J ) 7.4 Hz). 13C{1H} NMR (CDCl3): δ ) 152.2,
3
140.1, 137.9, 135.5, 134.7, 134.6, 132.9, 132.3, 131.5, 131.4, 131.3,
130.6, 130.5, 130.4, 129.7, 128.8, 127.8, 127.6, 127.4, 127.3, 126.7,
126.4, 126.1, 125.3, 125.2, 125.0, 124.6, 124.5, 124.3, 124.2, 124.1,
119.8, 94.5, 17.7, 17.6, 17.4, 17.3, 15.3, 15.2, 14.8, 14.7, 14.5. IR
(KBr): ν ) 3043 (m), 2960 (m), 2926 (m), 2868 (m), 2161 (m), 1597
(m), 1555 (s), 1479 (s), 1386 (m), 1360 (m), 1323 (m), 1184 (s), 1122
(m), 1062 (m), 977 (s), 846 (m). FAB+ (m/z, nature of peak, relative
intensity): 781.2, [M + H]+, 100. Anal. Calcd for C58H45BN2 (Mr )
780.80): C, 89.22; H, 5.81; N, 3.59. Found: C, 88.94; H, 5.67; N,
3.41.
Molecular orbital calculations were made on energy-minimized
conformations calculated by Gaussian 03 using the parametrized
semiempirical AM1 method and checking for imaginary frequencies.26
Several different starting geometries were sampled. Such AM1 calcula-
tions are far from definitive for boron-containing compounds but have
been found to adequately model cyclic boron ethers.27 Parameters for
boron were taken from the literature.28 These calculations were used
to generate energy-minimized geometries and transition dipole moments
for the dyes in vacuo. Molecular dynamics simulations (MDS) were
performed with INSIGHT-II29 running on a Silicon Graphics O2
workstation. Structures were drawn in the Builder module, and partial
charges were assigned using the ESFF force field.30 Energy minimiza-
tion was carried out with the Discover-3 module using the conjugate
gradient method with a cutoff of 9.5 Å until the maximum derivative
was less than 0.0005 kcal/Å. The energy-minimized geometries were
used as the starting points for the MDS studies. Each MDS run consisted
of an initial 10 ps of equilibration using the velocity scaling method,
followed by 100 ps of production dynamics. During the latter stage,
the temperature averaged 300 K, with a standard deviation of 4.8 K.
Data points were sampled each 10 fs of simulation time.
Spectroscopic Studies. Spectrophotometric grade solvents were
purchased from Aldrich Chemical Co. and used as received. Absorption
and fluorescence spectra were recorded using a Hitachi U3300
spectrophotometer and a fully corrected Yvon-Jobin Fluorolog Tau-3
spectrofluorimeter, respectively. Low-temperature emission spectra were
taken using an immersion-well liquid N2 Dewar. Emission quantum
yields were measured in N2-purged 2-methyltetrahydrofuran (MeTHF)
relative to Rhodamine 6G (in methanol)22 or Coumarin 153 (in
cyclohexane or ethanol/water 1:1).23 Corrections were made for changes
in refractive index24 or density as required. Fluorescence lifetimes were
recorded using the phase modulation method on an Yvon-Jobin
Fluorolog Tau-3 Lifetime System, with the instrumental response
function being measured against a solution of Ludox in distilled water.
Additional lifetime measurements were made with a PTI XenoFlash
system. All solutions used for fluorescence spectral measurements were
optically dilute and were used in conjunction with nonemissive glass
cutoff filters.
Flash photolysis studies were made with an Applied Photophysics
Ltd. LKS60 instrument. Excitation was made with 4-ns pulses at 532
nm, delivered with a frequency-doubled, Q-switched Nd:YAG laser,
while detection was made at 90° using a pulsed, high-intensity Xe arc
lamp. The signal was detected with a fast-response photomultiplier tube
after passage through a high-radiance monochromator. Transient
differential absorption spectra were recorded point-by-point, with five
individual records being averaged at each wavelength. Kinetic measure-
ments were made after averaging 50 individual records using global
analysis methods. The sample was purged with N2 before use. For some
studies, iodomethane (10% v/v) was added before photolysis. The laser
intensity was calibrated by reference to the triplet state of zinc meso-
tetraphenylporphyrin in deoxygenated toluene.25
Results and Discussion
Synthesis and Characterization. The three target compounds
were prepared in a single reaction using the difluoro derivative
(F-Bodipy) and half an equivalent each of 1-lithioethynylpyrene
and 1-lithioethynylperylene. Due to comparable reactivity, it
was anticipated that a statistical ratio of the dyes would be
formed. Separation of the three compounds was successfully
realized on several flash chromatography columns using ad-
equate mobile phases, followed by multiple recrystallizations.
The fingerprint of these molecules is given by the proton NMR
spectra. In particular, compound 1 exhibits a characteristic
doublet at 8.75 ppm, whereas for 2 a doublet is found at 8.37
ppm. In both cases, the integrations of these peaks correspond
Fast transient spectroscopy was made by pump-probe techniques
using femtosecond pulses delivered from a Ti:sapphire generator
amplified with a multipass amplifier pumped via the second harmonic
of a Q-switched Nd:YAG laser. The amplified pulse energies varied
from 0.3 to 0.5 mJ, and the repetition rate was kept at 10 Hz. Part of
the beam (ca. 20%) was focused onto a second harmonic generator in
order to produce the excitation pulse. The residual output was directed
onto a 4-mm sapphire plate so as to create a white light continuum for
detection purposes. The continuum was collimated and split into two
equal beams. The first beam was used as reference, while the second
(26) Frisch, M. J.; et al. Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford,
CT, 2004.
(27) Kuznetsov, V. V. J. Struct. Chem. 2001, 42, 494.
(28) (a) Dewar, M. J. S.; Reynolds, C. H. J. Comput. Chem. 1986, 2, 140. (b)
Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. P. J. Am. Chem.
Soc. 1985, 107, 3902. (c) Dewar, M. J. S.; McKee, M. L.; Rzepa, H. S. J.
Am. Chem. Soc. 1978, 100, 3607. (d) Dewar, M. J. S.; Thiel, W. J. Am.
Chem. Soc. 1977, 99, 4899. (e) Dewar, M. J. S.; Jie, C.; Zoebisch, E. G.
Organometallics 1988, 7, 513.
(22) Olmsted, J., III. J. Phys. Chem. 1979, 83, 2581.
(23) Jones, G., II; Rahman, M. A. J. Phys. Chem. 1994, 98, 13028.
(24) Eaton, D. F. Pure Appl. Chem. 1988, 60, 1107.
(25) (a) Hurley, J. K.; Sinai, N.; Linschitz, H. Photochem. Photobiol. 1983, 38,
9. (b) Carmichael, I.; Hug, G. L. J. Phys. Chem. Ref. Data 1986, 15, 1.
(29) INSIGHT-II; Accelrys Software Inc.: Cambridge, UK, 2001-2006.
(30) Shi, S.; Yan, L.; Yang, Y.; Fisher-Shaulsky, J.; Thacher, T. J. Comput.
Chem. 2003, 24, 1059.
9
10870 J. AM. CHEM. SOC. VOL. 128, NO. 33, 2006