Optical and electrochemical properties of ethynylaniline derivatives of phenothiazine, phenothiazine-5-oxide and phenothiazine-5,5-dioxide

Article abstract of DOI:10.1039/c4cp00678j

Three phenothiazine (PTZ) derivatives with varying degrees of sulfur oxidation states were synthesized as strong electron donors. The thioether, sulfoxide and sulfone PTZ-derivatives exhibited irreversible oxidation at 0.19 V, 0.29 V and 0.31 V versus ferrocene, respectively. Each PTZ derivative was emissive with lifetimes of 1.7 ns, 0.5 ns, and 0.5 ns and absolute quantum yields of 0.32, 0.23 and 0.23 for the thioether, sulfoxide and sulfone derivatives, respectively. Furthermore, these PTZ derivatives showed very large Stokes shifts ranging from 5600 cm^-1 to 2800 cm^-1. Calculations using DFT and TD-DFT methods resulted in an optimized ground state and the excited state geometries of the PTZ derivatives that compared favourably to experimental optical and electrochemical data. DFT calculations revealed that these butterfly shaped derivatives flatten upon excitation and this effect is greatest for the thioether PTZ derivative, resulting in the large Stokes shift. These potent electron donor systems also displayed electrochromic behaviour upon oxidation, which was attributed to a delocalized cation over the phenothiazine core and the appended ethynyl anilines. The electrochemically oxidized species had a wide absorption profile spanning from 300 nm to past 800 nm.

Full text of DOI:10.1039/c4cp00678j

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Optical and electrochemical properties of
ethynylaniline derivatives of phenothiazine,
phenothiazine-5-oxide and phenothiazine-5,5-
dioxide†
Cite this: Phys.Chem.Chem.Phys.,
2014, 16, 12266
Kim D. Theriault and Todd C. Sutherland*
´
Three phenothiazine (PTZ) derivatives with varying degrees of sulfur oxidation states were synthesized as strong
electron donors. The thioether, sulfoxide and sulfone PTZ-derivatives exhibited irreversible oxidation at 0.19 V,
0.29 V and 0.31 V versus ferrocene, respectively. Each PTZ derivative was emissive with lifetimes of 1.7 ns,
0.5 ns, and 0.5 ns and absolute quantum yields of 0.32, 0.23 and 0.23 for the thioether, sulfoxide and sulfone
derivatives, respectively. Furthermore, these PTZ derivatives showed very large Stokes shifts ranging from
5600 cmꢀ1 to 2800 cmꢀ1. Calculations using DFT and TD-DFT methods resulted in an optimized ground state
and the excited state geometries of the PTZ derivatives that compared favourably to experimental optical and
electrochemical data. DFT calculations revealed that these butterfly shaped derivatives flatten upon excitation
and this effect is greatest for the thioether PTZ derivative, resulting in the large Stokes shift. These potent
electron donor systems also displayed electrochromic behaviour upon oxidation, which was attributed to a
delocalized cation over the phenothiazine core and the appended ethynyl anilines. The electrochemically
oxidized species had a wide absorption profile spanning from 300 nm to past 800 nm.
Received 14th February 2014,
Accepted 25th April 2014
DOI: 10.1039/c4cp00678j
www.rsc.org/pccp
Our approach was to install electron rich functionality, via
dialkylanilines, that are bridged through a conjugated spacer to
Introduction
Phenothiazine (PTZ) has a long and rich history, beginning enhance the donor capability of PTZ. The alkyne spacer was deemed
in the late 19th century of its use as a dye molecule,1 such as as important to permit co-planarity between the aniline and the PTZ
Lauth’s violet and methylene blue. PTZ derivatives regained for more effective p-donation. The alkyne spacer should impart
popularity in pharmacology due to the reversal of multidrug desirable optical effects due to the extended conjugation and may
resistance.2,3 More recently, PTZ was explored as an organic alter the electrochemical oxidation properties. The goal of this work
semiconductor because it possesses a high lying HOMO energy is to explore these PTZ derivatives as candidate electrons donors for
and was considered as an electron-donating (p-type) building organic electronic applications. In addition, we investigated the
block.4 Owing to its strong electron donating character, several effect of oxidizing the sulfur in the thiazine ring to potentially access
synthetic derivatives of PTZ explored the electronic tunability intramolecular donor–acceptor electronic interactions, as observed
by electron-donating and electron-withdrawing substituents for in phenoxazine19 and dibenzoazaborine20,21 systems.
semiconductor applications.5–8
Structurally, the thiazine heterocycle of PTZ is non-planar
The PTZ core and its atom numbering are shown at the top and several researchers have solved single-crystal X-ray struc-
of Scheme 1. Regioselective derivatization of PTZ has been tures showing that the angle between planes of the annulated
extensively explored in the literature and the most common benzo groups range from 138 to 156 degrees.22–28 The angle
substituents are at the nitrogen and the 3,7-positions. Of the between planes of the annulated benzo groups of the congeners
over one thousand 3,7-PTZ derivatives reported, there are only typically widens with increasing oxidation of the sulphur:
ten reports of PTZ derivatized with an alkyne functionality.9–18 145 to 162 degrees for the sulfoxide22,26,29–34 and 134–163
degrees for the sulfone.23,32,33,35–37 However, there is significant
Department of Chemistry, University of Calgary, 2500 University Drive NW,
Calgary Alberta, Canada. E-mail: todd.sutherland@ucalgary.ca;
Fax: +1 403 289 9488; Tel: +1 403 220 7559
overlap between angle ranges and the different sulfur oxidation
states, implying that the thiazine ring is rather flexible and its
structure is determined by both synthetic derivatization and
crystal packing. Interestingly, the non-planar thiazine ring in
PTZ is speculated to be responsible for the large Stokes shifts
observed in the fluorescence spectra.
† Electronic supplementary information (ESI) available: Calculated geometries of
ground and excited states; cyclic voltammograms; differential pulse voltammo-
grams; FTIR spectra; 1H and 13C NMR spectra; fluorescence lifetime measure-
ments. See DOI: 10.1039/c4cp00678j
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Optical properties
The absorption and fluorescence spectra of 3a to 3c in CH2Cl2 are
shown in Fig. 1 and relevant optical data are summarized in Table 1.
All three PTZ derivatives show intense optical transition from
400 nm and below. Both PTZ sulfoxide and sulfone (3b and 3c)
show near superimposable absorption spectra, whereas compound
3a has a different absorption profile. Clearly, the sulfur oxida-
tion state has an effect on the intensity of the optical transi-
tions. PTZ 3a has the lowest energy absorption onset, calculated
by the intersection between absorption and fluorescence, at
2.8 eV compared to both sulfoxide 3b and sulfone 3c at 3.0 eV.
Each PTZ derivative is moderately fluorescent in solution with
quantum yields of 0.32 for 3a and 0.23 for both 3b and 3c. The
fluorescence lifetime of 3a is the longest at 1.7 ns, while 3b and
3c have similar lifetimes of 0.5 ns.
Most notable in the emission of 3a is the large Stokes shift
of 5600 cmꢀ1 as compared to 3b and 3c with Stokes shifts of
2800 cmꢀ1 and 2900 cmꢀ1, respectively. Such a large Stokes shift
for PTZ derivatives has been reported previously43,44 and is
attributed to a significant structural change occurring in the S1
energy surface. The large change in structure is presumably the
result of the bent ground-state structure becoming more planar
in the excited state. Here, we postulate that the oxidation of the
sulfur hinders the PTZ excited states from adopting the more
planar structure, which results in a smaller Stokes shift for 3b
and 3c, and these optical and structural properties are discussed
further in the computational section.
Scheme 1 Synthesis of ethynylaniline PTZ oxides 3a–3c.
A closer examination of the fluorescence spectrum of 3a
shows a distinct peak and a lower energy shoulder, which are
Here we present the synthesis of three bis-alkynylaniline
PTZ derivatives, shown in Scheme 1, with the sulfur of the
thiazine ring in the S(II), S(IV) and S(VI) oxidation states. The
effects of the different sulfur oxidation states are explored using
optical absorption spectroscopy, fluorescence spectroscopy,
electrochemistry and spectroelectrochemistry and the results
are interpreted by comparison to DFT-calculations. Appending
dialkyl ethynylanilines to the PTZ core gives organic soluble
building blocks that could lead to uniform thin films.
Results and discussion
Synthesis
The synthesis of the ethynylaniline-PTZs, shown in Scheme 1,
begins with N-alkylating PTZ under the typical conditions
reported by Sailer.38 We elected to install decyl chains early
in the synthesis to aid in organic solubility for subsequent
purification steps. Regioselective electrophilic bromination also
followed methods in the literature39,40 to give 3,7-dibrominated
precursor 2a in modest yields. The PTZ core building block 2a
was subjected to either mild (Cu2+) or strong (mCPBA) oxidizing
Fig. 1 Absorption and fluorescence spectra of 3a (blue), 3b (green) and 3c
(black) in CH2Cl2. Excitation for the fluorescence spectra was set at the
lowest energy absorption band.
conditions, which resulted in sulfur oxidation to PTZ-5- Table 1 Optical properties of 3a–3c
oxide 2b41 or PTZ-5,5-dioxide 2c.42 The three different sulfur
lmax
/
lem
/
Stokes shift/
cmꢀ1
oxidation states of PTZ (2a–2c) were finally reacted under
Sonogashira conditions with N,N-didecyl-4-ethynylaniline to give
PTZ derivatives 3a to 3c, which are highly soluble in common
organic solvents.
Entry nm (eV)
nm (eV)
t/ns
f
3a
3b
3c
377 (3.2)/337 (3.7) 477 (2.6)/504 (sh) 5600
388 (3.2)/348 (sh) 435 (2.9)
388 (3.2)/348 (sh) 438 (2.9)
1.7 0.32
0.5 0.23
0.5 0.23
2800
2900
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resulted in poor linearity for both the absorption and emission
peaks. The ESI† contains the absorption and emission spectral
data for all the solvents and plots of two solvent scale approaches
to demonstrate the limitations of the single-parameter solvent
models in this PTZ system.
45
´
Instead, using Catalan’s approach, which combines two
specific scales (SA and SB) and two general scales (SP and SdP) a
multi-parameter, general approach was achieved to describe the
solvent interactions for both the absorption and emission peaks.
The detailed results of the fitting using the multi-parameter
approach is found in the ESI,† but the highlights are described
herein. All of the absorption peak data could be fitted with non-
specific scales, solvent polarizability (SP) and solvent dipolarizability
(SdP), with R2 values of 0.94 or greater. Interestingly, the emission
data required the inclusion of a solvent specific scale, solvent basicity
(SB), in addition to the non-specific SP and SdP terms to induce
reasonable fits to the emission data with R2 values of 0.98 or greater.
The SB term increased in significance in concert with the sulfur
oxidation state in the thiazine ring, suggesting specific solvent
to sulfur interactions in the excited state structure that are not
present in the ground-state.
Fig. 2 Solvatochromic properties of lowest energy absorption (hollow
points) and emission (solid points) bands for PTZs 3a (squares), 3b (circles)
and 3c (triangles) using the dipolarity index.
attributed to a vibronic side band with 1100 cmꢀ1 energy spacing.
The presence of vibronic bands in the fluorescence spectrum of 3a
Electrochemical properties
supports the notion of a more planar or rigid structure. The All three PTZ derivatives show irreversible oxidation reactions
absorption spectra of both 3b and 3c also show vibronic shoulders in DMF using cyclic voltammetry, as shown in the ESI† and no
and peaks in the lowest energy region with an energy spacing reduction reactions were observed within the solvent stability
of 2800 cmꢀ1
.
potential window. Oxidation potentials are reported versus an
Both the lowest energy absorption and emission peaks of internal ferrocene/ferricenium redox reaction using differential
PTZs 3a to 3c show solvatochromic effects, as depicted in Fig. 2. pulse voltammetry (DPV). PTZ derivatives 3a to 3c show increasing
The absorption energy is highest in low polarity solvents, such oxidation potentials of 190 mV, 285 mV and 310 mV, respectively.
as hexanes, and lowest in a moderate polarity CH2Cl2 solvent The stepwise increment in the oxidation potential is consistent
and again increases absorption energy in the polar acetonitrile. with the change in the oxidation state of sulfur and stabilization
The absorption bands shift by approximately 1000 cmꢀ1 over of the HOMO with electron withdrawing groups. For comparison,
the range of solvents examined. The emission profiles of 3a to the TMS-protected ethynyl aniline precursor shows an oxidation
3c show different solvatochromic behaviours. PTZ 3a displays potential of 400 mV under the same electrochemical conditions.
small perturbations over the solvent range (Dnem = 630 cmꢀ1), PTZ, under the same conditions, gives an oxidation potential of
whereas sulfone PTZ, 3c, exhibits a large spectral response to 150 mV, which is even lower than 3a suggesting that the ethynyl
different solvents that span approximately 3700 cmꢀ1. PTZ 3b anilines act as electron withdrawing groups in these compounds.
shows intermediary solvatochromic emission relative to 3a and That no reduction peaks were observed within the solvent stability
3c. We have elected to use the solvent dipolarity (SdP) empirical window suggests that the change in sulfur oxidation state on the
45
´
scale, as described by Catalan, to plot the absorption and thiazine ring has minimal effect on lowering the LUMO energy.
emission peaks, as shown in Fig. 2. The SdP scale gave the most
linear correlation to the absorption and emission peak data.
Computations
Clearly, the single-parameter SdP scale does not adequately Truncated models of the three final PTZ derivatives (Me groups
describe the complexities of the solvent interactions. Solvent replaced alkyl chains) were investigated using Density Func-
effects can be divided into two interactions – specific and non- tional Theory (DFT) and time-dependent (TD)-DFT calculations
specific. Several solvent scales have been parameterized to describe including solvent effects of the polarisable continuum model
46
´
the specific donor–acceptor interactions, such as Catalan’s SA
(PCM) at the B3LYP/6-31G+(d) level. Computational results using
and SB47 scales, Kamlet and Taft’s a and b,48,49 Gutman’s AN Gaussian0958 with dichloromethane as the solvent provide insight
and DN scales50 and Drago’s EB and CB51 scales to name a few. into the absorption and emission energies and provide key insight
Non-specific interactions where the solvent is treated as a into the structural changes following excitation.
dielectric continuum were originally modelled by Kirkwood52
All of the optimized ground state structures are butterfly-shaped
and Onsager,53 and have been empirically parameterized by the about the thiazine ring, as shown in Fig. 3. Note the sulfoxide
Dong and Winnik’s Py scale,54 Kamlet, Abboud and Taft’s p* derivative has two possible thiazine ring conformations: S–O
scales,55 Drago’s S0 scale and Catalan’s SPP scale. Many of bond boat-axial (3bax) and S–O bond boat-equatorial (3beq).29
56
57
´
the single parameter solvent scales were attempted here and Calculations show a small energetic preference of 8.3 kJ molꢀ1
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Fig. 3 (a) DFT optimized ground state structures of 3a, 3beq and 3c, their FMOs and orbital energies using the B3LYP/6-31G+(d,p) basis set. (b) TD-DFT,
using the same functional and basis set, calculations of S0 and S1 structures of 3a, 3bax and 3c and their associated calculated absorption and emission
peak energies.
for the axial S–O isomer and FT-IR results, included in the ESI,† were PTZ derivatives. The energies of the absorption transitions
inconclusive as to the isomer formed upon oxidation. The optimized (S0 to S1) were approximately 420 nm (3.0 eV) for all of the
ground-state structure exhibited angles between planes (calculated PTZ derivatives, which is slightly lower in energy than
by the intersection of the two imaginary planes extending from the the experimental values for 3a–3c at 3.2 eV, determined by
annulated benzo groups) of 1451, 1411, 1491 and 1481 for 3a, 3beq, the lmax value. The first excited state structure, S1, was then
3bax and 3c, respectively, as depicted in Fig. 3b. In addition, the optimized in the presence of DCM and additional TD-DFT
optimized ground-state geometry resulted in dipole moments of calculations were carried out to assess the emission energy.
2.12 D, 7.69 D and 7.40 D, for 3a, 3bax and 3c, respectively.
Fig. 3b summarizes the results of the TD-DFT calculations and
The FMOs and orbital energies are shown in Fig. 3a. The highlights the structural changes that occur in the first excited
thiazine derivative, 3a, has the highest HOMO energy of the states following literature calculation methods.60,61
series, as expected for such an electron-rich species. There is a
All three PTZ derivatives exhibit significantly red-shifted
decrease in the HOMO energy when oxidizing to the sulfoxide emission energies compared to the absorption energies, which
and a further HOMO stabilization upon sulfone generation, supports the results of the experimentally observed Stokes shifts.
leading to an overall HOMO tunability range of 0.16 eV. The Although, the absolute energy values are not directly comparable
limited range of HOMO energy tunability over the series of to the experimental values, the same trend is apparent and the
PTZs likely reflects the delocalized contributions from the computations provide insight into the associated structural
ethynyl-anilines. The HOMO coefficients of PTZs 3a to 3c are changes in the excited states. The first singlet excited state (S1)
representative of a delocalized p-system over the entire con- structure of PTZ 3a is significantly more planar compared to its
jugated system. Of notable difference is the coefficient on the ground-state, S0, structure, which is consistent with the largest
sulfur atom in PTZ 3a, whereas both 3b and 3c have nodes on Stokes shift in the series and appearance of vibronic bands in
sulfur. A similar decreasing energy trend in LUMO energies is the fluorescence spectrum. The boat geometry of the thiazine
found through the series of 3a to 3c. The LUMO shapes of 3a–3c ring changes from 1451 to 1621 in 3a. For PTZ 3b, both boat S–O
are nearly identical showing p-delocalized systems with nodes axial and equatorial structures were computed in S0 and S1
at both the nitrogen and sulfur atoms of the thiazine ring. The states. Interestingly, only the axial structure 3bax, mirrored both
HOMO energy levels for 3a, 3beq, 3bax and 3c using DFT the absorption and emission experimental data, supporting
methods are ꢀ4.97 eV, ꢀ5.07 eV, ꢀ5.08 eV and ꢀ5.13 eV versus the notion that the Cu-mediated oxidation mechanism yields
vacuum, respectively, compare favourably to the electrochemically- exclusively the axial product. The boat geometry of the 3bax
determined HOMO energy levels at ꢀ5.0 eV, ꢀ5.1 eV and ꢀ5.1 eV thiazine oxide ring changes from 1491 to 1521. The S0 and S1
(using Fc/Fc+ redox standard at ꢀ4.8 eV),59 for 3a to 3c.
structures of the S–O boat equatorial derivative, 3beq, as calcu-
TD-DFT calculations using DCM as a solvent resulted in lated by DFT methods showed absorption and emission peaks
strong and exclusive HOMO to LUMO transitions in all three at 418 nm and 497 nm, respectively. The ground state geometry
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Each PTZ derivative shows the growth of an intense, red-shifted
absorption profile that spans from 300 nm to over 800 nm,
which is consistent with a highly delocalized cation charge.
PTZ 3a shows the most intense absorption with a broad peak
centred at 680 nm. Compounds 3b and 3c share a similar
absorption profile with peaks at 670 nm and 680 nm, respec-
tively. Each absorption spectrum shown in Fig. 4 was recorded
at 1 minute intervals for approximately 20 minutes. Clear
isosbestic points are observed in each set of spectra at approxi-
mately 412 nm, which suggests either a stable radical cation
that is electrochemically irreversible, or a chemical reaction
following the electrochemical oxidation to form a new optically-
active compound.
Most importantly, because these alkyne anilines are able to
stabilize the oxidized PTZ to such a great extent these oxidized
species could find applications into potent low energy photon
absorbing materials, electrochromics or as p-type molecular
candidates in organic electronic applications.
Conclusions
We have successfully synthesized an alkynyl aniline-PTZ adduct by
exploiting Sonogashira reaction conditions to produce a set of
potent electron donating, p-type, organic semi-conductor candi-
dates. Optically, the neutral PTZ derivatives show modest absorption
properties (o450 nm), but all derivatives are strongly emissive with
large Stokes shifts of up to 5600 cmꢀ1 and both absorption and
emission peaks are solvatochromic. All three donors exhibited
irreversible oxidation potentials as low as 0.19 V vs. Fc/Fc+ and
none of the PTZ derivatives displayed reductions within the solvent
window, despite chemical oxidation to the thiazine-dioxide. TD-DFT
calculations and optimizations show a reasonable correlation with
experimental data and indicate that the PTZ derivatives become
more planar in the excited state, rationalizing the large Stokes shift.
Furthermore, the computationally-derived optical spectra support
the S–O boat axial isomer over the equatorial S–O isomer. Upon
electrochemical oxidation, all PTZ-derivatives exhibited a dramatic
colour change owing to the delocalized cation through the PTZ core
and appended ethynyl anilines that resulted in its absorption profile
spanning from 300 nm to over 800 nm.
Fig. 4 Spectroelectrochemical evolution of the 3a–3c (ca. 10ꢀ5 M in
DMF) upon application of an oxidizing potential at the onset of oxidation
determined from CV experiments. Each spectrum is taken at 1 minute
intervals and the initial spectrum is a grey line that evolves to a black line
over the time course of the experiment.
of 3beq is very similar to the 3bax derivative; however, the S1
optimized structure of 3beq is more planar than the S–O axial
structure leading to a significant red-shift in emission, which
the experimental data do not support. Clearly, the boat axial
S–O of 3bax inhibits the planarization of the PTZ leading to a
smaller Stokes shift compared to that of 3a. The optimized S0
and S1 structures of PTZ dioxide, 3c, behaves very similarly to
3bax with a change in the boat thiazine dioxide ring geometry of
1481 to 1531 upon excitation. The excited-state dipole moments
of 3a, 3bax and 3c are expectedly lower due to planarization
than the S0 structures at 0.87 D, 7.34 D and 6.79 D, respectively.
Upon generation of the S1 state, there is a contraction of the
thiazine of both the N–C and S–C bonds, which we speculate
helps in planarization, as has been described previously in the
radical cation structure of PTZ.62
Experimental section
Materials
All chemicals were purchased from Aldrich and used as received
without further purification, aside from the following: aniline was
purchased from BHD, K2CO3 was purchased from EMD and
Pd(PPh3)2Cl2 was purchased from Strem. Solvents were used as
received or dried using an MBraun solvent purification system.
THF, DMF and DCM were stored over sieves before use and
triethylamine was distilled in the presence of CaH and stored over
Spectroelectrochemistry
All three final PTZ derivatives are electron donors in addition to sieves. Column chromatography was performed on a SiliCycle
being highly conjugated; consequently, their absorption profile SilicaFlash P60 silica gel (230–400 mesh). Thin-layer chromato-
changes during the oxidation reaction were investigated. The evolu- graphy was carried out on Merck silica gel F254 aluminium-
tions of the absorption spectra for 3a to 3c are shown in Fig. 4. backed TLC plates.
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General
6: N,N-Didecyl-4-((trimethylsilyl)ethynyl)aniline. A yellow mixture
of 5 (9.2376 g, 18.5 mmol), bis(triphenylphosphine)palladium(II)
dichloride (0.6343 g, 0.90 mmol), triphenyl phosphine (0.7295 g,
2.78 mmol) and copper(I) iodide (0.3893 g, 2.04 mmol) in dry
triethylamine (50 mL) was purged with N2. Trimethylsilyl-
acetylene (5.3 mL, 37.2 mmol) was added by syringe over 20 minutes.
The reaction mixture was stirred at room temperature and
under N2 overnight. The solvent was removed from the brown
mixture in vacuo and the crude product was purified using
silica gel chromatography hexanes : DCM (1 : 1) to give 6 as an
NMR spectra were recorded on a Bruker 400 MHz spectrometer
and referenced to residual CHCl3 in CDCl3 (1H 7.26 ppm, 13C
77.00) or residual (CH3)2CO in (CD3)2CO (1H 2.05 ppm). Mass
spectra were recorded with an Agilent 6520 LC Q-TOF spectro-
meter run in ESI mode by direct infusion with the column
bypassed. All samples were dissolved in DCM and run with an
eluent flow rate of 0.2 mL minꢀ1 MeOH, source temperature of
200 1C, fragmenter voltage of 120 V, Nebulizer pressure of 12 psi
and a drying gas flow rate of 7 L minꢀ1. FTIR spectra were
recorded in diffuse reflectance mode with drop-cast films on
ground KBr on a Varian FTS-7000 spectrometer. UV/Vis spectra
were recorded using a Cary 5000 spectrophotometer in dual
beam mode. Emission spectra were recorded using a Photon
Technology International (PTI) Quanta Master spectrofluorimeter
operated in CW mode, with samples in a quartz Suprasil cell
(1 cm width and path length, Hellma, Canada). Lifetime measure-
ments were obtained at room temperature using an Edinburgh
Instruments FLS920 spectrometer equipped with Fianium SC400
Super Continuum White Light Source, Hamamatsu R3809U-50
Multi Channel Plate detector and data were analyzed using
Edinburgh Instruments F900 software. Curve fitting of the data
was performed using a non-linear least squares procedure in the
F900 software. Absolute fluorescence quantum yield values were
measured using an Edinburgh Instruments FLS92 calibrated
integrating sphere S 3 system.
4: N,N-Didecylaniline. Potassium carbonate (3.0640 g, 32.9 mmol)
and 1-bromodecane (25 mL, 120.8 mmol) were added to a
solution of aniline (3 mL, 32.9 mmol) in DMF (100 mL) and
refluxed overnight. A blue colour appeared during the reaction but
disappeared after completion. The solid residues were removed by
filtration followed by removal of solvent in vacuo. The crude
product was then reconstituted in diethyl ether, washed with
water and the organic fraction was dried with magnesium sulfate.
Removal of solvent in vacuo afforded a golden oil, which was
purified by silica gel column chromatography (DCM) and resulted
in a light yellow oil (11.7821 g, 95.8%).
5: N,N-Didecyl-4-iodoaniline. A solution of 4 (11.6409 g,
31.2 mmol) in dioxane : pyridine (1 : 1, 280 mL) was cooled
in an ice bath. Iodine (19.1842 g, 75.6 mmol) was then added
and the reaction mixture was stirred for 1 hour. Unreacted
iodine was removed with saturated aqueous sodium thiosulfate
(250 mL). Water (250 mL) was added to the organic fraction, then
the product was extracted with DCM, dried with magnesium
sulfate and the solvent was removed in vacuo to afford a blue oil
as the crude product. Further purification with silica gel
column chromatography hexanes : DCM (4 : 1) yielded 5 as a
light yellow oil (12.1775 g, 78.2%). 1H NMR (400 MHz, CDCl3) d
7.46 (d, J = 9.1 Hz, 2H), 6.46 (d, J = 9.1 Hz, 2H), 3.30–3.23
(m, 4H), 1.66–1.55 (m, 4H), 1.43–1.29 (m, 28H), 0.97 (t, J =
6.9 Hz, 6H). 13C NMR (101 MHz, CDCl3) d 147.70, 137.72,
114.13, 75.53, 51.12, 32.04, 29.80, 29.78, 29.75, 29.73, 29.72,
29.70, 29.68, 29.66, 29.49, 29.48, 29.47, 29.45, 29.45, 27.29,
27.27, 27.21, 22.83, 14.26, 14.24. MS (ESI HRMS) m/z calcd for
1
orange oil (8.4001 g, 96.7%). H NMR (400 MHz, CDCl3) d 7.35
(d, J = 9.0 Hz, 2H), 6.56 (d, J = 9.0 Hz, 2H), 3.34–3.24 (m, 4H),
1.68–1.55 (m, 4H), 1.47–1.29 (m, 28H), 0.98 (t, J = 6.9 Hz, 6H),
0.31 (s, 9H). 13C NMR (101 MHz, CDCl3) d 148.07, 133.32,
111.10, 108.96, 107.03, 90.61, 51.00, 32.05, 29.79, 29.72, 29.65,
29.48, 27.33, 27.24, 22.82, 14.22, 0.37. MS (ESI HRMS) m/z calcd
for C31H56NSi + H: 470.4177; found 470.4162.
7: N,N-Didecyl-4-ethynylaniline. A solution of TBAF (21 ml,
1 M in THF) was added to a solution of 6 (8.4001 g, 16.8 mmol) in
DCM (25 mL) and the mixture was stirred at room temperature
for 1 hour. The mixture was then washed with brine and H2O,
dried with magnesium sulfate and reduced in vacuo to obtain the
crude product as a brown oil. The product was purified with
silica gel column chromatography hexanes : DCM (1 : 1) to afford
7 as an orange oil (6.0262 g, 90.1%). 1H NMR (400 MHz, CDCl3)
d 7.35 (d, J = 8.9 Hz, 2H), 6.55 (d, J = 9.0 Hz, 2H), 3.31–3.24
(m, 4H), 2.97 (s, 1H), 1.64–1.54 (m, 4H), 1.40–1.25 (m, 28H), 0.92
(t, J = 6.8 Hz, 6H). 13C NMR (101 MHz, CDCl3) d 148.34, 133.47,
111.19, 107.67, 85.21, 74.49, 51.08, 32.04, 29.80, 29.71, 29.66,
29.47, 27.34, 27.27, 22.82, 14.24. MS (ESI HRMS) m/z calcd for
C28H48N + H: 398.3781; found 398.3770.
1: 10-Decyl-10H-phenothiazine. A mixture of phenothiazine
(5.1028 g, 25.6 mmol) and potassium tert-butoxide (3.1200 g,
mmol) in dry THF (50 mL) was purged with N2 before adding
1-bromodecane (10.4 mL, 50.3 mmol). The mixture was refluxed
under N2 overnight. Removal of the solids residues by filtration and
the solvent in vacuo gave a brown oil. The crude product was
purified by silica gel chromatography (hexanes - hexanes : DCM
1
(9 : 1)) to afford 1 as a light yellow oil (5.6460 g, 64.9%). H NMR
(400 MHz, acetone) d 7.17 (t, J = 7.7 Hz, 2H), 7.12 (d, J = 7.6 Hz, 2H),
6.98 (d, J = 8.1 Hz, 2H), 6.92 (t, J = 7.5 Hz, 2H), 3.90 (t, J = 6.7 Hz,
2H), 1.83–1.71 (m, 2H), 1.50–1.38 (m, 2H), 1.35–1.18 (m, 12H), 0.87
(t, J = 6.7 Hz, 3H). 13C NMR (101 MHz, CDCl3) d 145.31, 127.37,
127.12, 124.97, 122.27, 115.37, 47.38, 31.96, 29.61, 29.55, 29.36,
29.30, 26.97, 26.91, 22.76, 14.22. MS (ESI HRMS) m/z calcd for
C22H29NS + H: 340.2099; found 340.2071.
2a: 3,7-Dibromo-10-decyl-10H-phenothiazine. A solution of 1
(3.8843 g, 11.4 mmol) in CHCl3 : AcOH (1 : 1, 750 mL) was
cooled in an ice bath and shielded from direct light. NBS
(5.4973 g, 30.9 mmol) was then added in three equal portions with
an hour between each addition. One hour after the last addition of
NBS, water was added when the reaction mixture was still cold. The
organic layer was removed, washed with H2O until the washes were
neutral and dried with magnesium sulfate to give a red oil once the
solvent was removed in vacuo. Further purification with silica gel
chromatography hexanes : DCM (9 : 1) gave 2a as a light yellow
C
26H47IN + H: 500.2748; found 500.2734.
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oil (2.7872 g, 49.0%). 1H NMR (400 MHz, CDCl3) d 7.21 (dd, d 147.82, 143.95, 132.71, 130.30, 129.81, 124.09, 118.36, 114.98,
J = 8.6, 2.3 Hz, 2H), 7.18 (d, J = 2.2 Hz, 2H), 6.65 (d, J = 8.6 Hz, 111.21, 108.86, 90.64, 86.26, 50.97, 47.62, 31.89, 29.65, 29.56,
2H), 3.79–3.66 (m, 2H), 1.79–1.68 (m, 2H), 1.45–1.35 (m, 2H), 29.51, 29.31, 29.20, 27.22, 27.14, 26.82, 22.67, 14.10. MS (ESI
1.35–1.22 (m, 12H), 0.92 (t, J = 6.9 Hz, 3H). 13C NMR (101 MHz, HRMS) m/z calcd for C78H119N3S + H: 1130.9197; found
CDCl3) d 143.79, 129.89, 129.40, 126.16, 116.39, 114.54, 47.40, 1130.9192.
31.78, 29.41, 29.36, 29.18, 29.05, 26.66, 26.47, 22.60, 14.10. MS
(ESI HRMS) m/z calcd for C22H27Br2NS + H: 496.0304; found 2,1-diyl)bis(N,N-didecylaniline). A yellow mixture of 2b (0.3904 g,
496.0308. 0.76 mmol), bis(triphenylphosphine)palladium(II) dichloride
3b: 4,40-(10-Decyl-5-oxide-10H-phenothiazine-3,7-diyl)bis(ethyne-
2b: 3,7-Dibromo-10-decyl-5-oxide-10H-phenothiazine. A solution (0.0535 g, 0.076 mmol), triphenyl phosphine (0.0600 g,
of 2a (1.0751 g, 2.16 mmol) and Cu(NO3)2ꢁ2.5H2O (1.4297 g, 0.23 mmol) and copper(I) iodide (0.0310 g, 0.16 mmol) in dry
6.15 mmol) in DCM (40 mL) was sonicated under ambient condi- triethylamine (24 mL) was purged with N2. A sparged solution
tions for 1 hour. The solid residue was removed by filtration and the of 7 (0.9960 g, 2.3 mmol) in triethylamine (22 mL) was added by
solvent was removed in vacuo to afford a yellow mixture. The crude syringe at a rate of 0.02 mL minꢀ1 while the mixture was stirred
product was purified by silica gel column chromatography DCM : under N2. The solvent was removed from the brown mixture
EtOAc (9 : 1) to give 2b as a light beige oil that solidifies upon in vacuo and the crude oil was purified using silica gel chro-
standing (0.6849 g, 61.5%). 1H NMR (400 MHz, CDCl3) d 8.01 matography DCM : EtOAc (99 : 1) to give 3b as a golden oil
(d, J = 2.4 Hz, 2H), 7.68 (dd, J = 9.0, 2.4 Hz, 2H), 7.27 (d, J = 9.1 Hz, (0.2941 g, 33.7%). 3b is fairly stable in air but when exposed
2H), 4.16–4.09 (m, 2H), 1.94–1.83 (m, 2H), 1.53–1.44 (m, 2H), 1.44– to light while in solution, it decomposes to a deep green
1.22 (m, 12H), 0.89 (t, J = 6.9 Hz, 3H). 13C NMR (101 MHz, CDCl3) d substance. 1H NMR (400 MHz, CDCl3) d 8.06 (d, J = 2.0 Hz,
137.03, 135.82, 133.67, 125.83, 117.70, 114.01, 48.50, 31.96, 29.65, 2H), 7.69 (dd, J = 8.8, 2.0 Hz, 2H), 7.39 (d, J = 8.8 Hz, 4H), 7.32
29.59, 29.37, 29.33, 26.84, 26.33, 22.77, 14.23. MS (ESI HRMS) m/z (d, J = 9.0 Hz, 2H), 6.59 (d, J = 9.0 Hz, 4H), 4.22–4.10 (m, 2H),
calcd for C22H27Br2NOS + H: 512.0258; found 512.0249.
3.35–3.22 (m, 8H), 2.00–1.86 (m, 2H), 1.66–1.55 (m, 8H), 1.55–
2c: 3,7-Dibromo-10-decyl-5,5-dioxide-10H-phenothiazine. A 1.47 (m, 2H), 1.47–1.39 (m, 2H), 1.39–1.23 (m, 66H), 0.96–0.87
solution of 2a (0.5040 g, 1.01 mmol) in DCM (10 mL) was (m, 15H). 13C NMR (101 MHz, CDCl3) d 147.93, 136.58, 135.25,
cooled in an ice bath before addition of mCPBA (75%, 0.7944 g, 134.35, 132.79, 124.11, 118.14, 115.60, 111.15, 108.33, 91.79,
3.45 mmol). The reaction mixture was stirred overnight as the 85.55, 50.90, 31.83, 29.60, 29.51, 29.46, 29.25, 29.21, 27.16,
temperature was allowed to slowly rise to room temperature. 27.07, 26.73, 22.63, 14.06. MS (ESI HRMS) m/z calcd for
The crude product was purified by silica gel column chromato-
graphy (DCM) to give 2c as a light brown oil (0.4317 g, 80.5%).
C
78H119N3SO + H: 1146.9147; found 1146.9120.
3c: 4,40-(10-Decyl-5,5-dioxide-10H-phenothiazine-3,7-diyl)bis-
1H NMR (400 MHz, CDCl3) d 8.16 (d, J = 2.4 Hz, 2H), 7.67 (dd, (ethyne-2,1-diyl)bis(N,N-didecylaniline). A yellow mixture of 2c
J = 9.1, 2.4 Hz, 2H), 7.20 (d, J = 9.1 Hz, 2H), 4.11–4.02 (m, 2H), (0.3039 g, 0.57 mmol), bis(triphenylphosphine)palladium(II)
1.89–1.78 (m, 2H), 1.47–1.37 (m, 2H), 1.37–1.19 (m, 12H), 0.87 dichloride (0.0445 g, 0.063 mmol), triphenyl phosphine (0.0472 g,
(t, J = 6.8 Hz, 3H). 13C NMR (101 MHz, CDCl3) d 139.64, 136.27, 0.18 mmol) and copper(I) iodide (0.0193 g, 0.10 mmol) in dry
126.23, 125.51, 118.15, 114.46, 48.75, 31.94, 29.57, 29.53, 29.33, triethylamine (25 mL) was purged with N2. A sparged solution
29.22, 26.79, 26.63, 22.75, 14.22. MS (ESI HRMS) m/z calcd for of 7 (0.7010 g, 1.76 mmol) in triethylamine (22 mL) was added
C
22H27Br2NO2S + Na: 550.0021; found 550.0020.
3a: 4,40-(10-Decyl-10H-phenothiazine-3,7-diyl)bis(ethyne-2,1- was stirred under N2. The solvent was removed from the brown
using a syringe at the rate of 0.02 mL minꢀ1 while the mixture
diyl)bis(N,N-didecylaniline). A yellow mixture of 2a (0.5104 g, mixture in vacuo and the crude product was purified using
1.03 mmol), bis(triphenylphosphine)palladium(II) dichloride silica column chromatography hexanes : DCM (2 : 3) to give a
(0.1539 g, 0.22 mmol), triphenyl phosphine (0.1714 g, 0.65 mmol) yellow oil that solidifies upon standing (0.4242 g, 63.6%).
and copper(I) iodide (0.0713 g, 0.37 mmol) in dry triethylamine 1H NMR (400 MHz, CDCl3) d 8.24 (d, J = 2.0 Hz, 2H), 7.65
(25 mL) was purged with N2. A sparged solution of 7 (1.2258 g, (dd, J = 8.9, 1.2 Hz, 2H), 7.37 (d, J = 8.9 Hz, 4H), 7.23 (d, J =
3.08 mmol) in triethylamine (22 mL) was added using a syringe 9.0 Hz, 2H), 6.58 (d, J = 9.0 Hz, 4H), 4.15–4.03 (m, 2H), 3.35–3.22
at the rate of 0.02 mL minꢀ1 and left to stir for 2 weeks. (m, 8H), 1.98–1.80 (m, 2H), 1.67–1.52 (m, 8H), 1.51–1.42
Additional sparged dry triethylamine (25 ml) was added to (m, 2H), 1.42–1.22 (m, 68H), 0.90 (t, J = 6.8 Hz, 15H). 13C
reconstitute the solvent volume, then a second portion of a NMR (101 MHz, CDCl3) d 148.09, 138.90, 135.38, 132.89, 126.27,
sparged solution of 7 (1.4430 g, 3.62 mmol) in dry triethylamine 124.19, 118.46, 115.95, 111.19, 108.14, 92.44, 85.32, 50.94,
(22 mL) was added by syringe at a rate of 0.02 mL minꢀ1 and 31.87, 31.84, 29.63, 29.54, 29.49, 29.45, 29.29, 29.25, 29.15,
stirred for 2 days. The solvent was removed in vacuo and the 27.20, 27.11, 26.73, 26.60, 22.65, 14.08. MS (ESI HRMS) m/z
crude product was purified using silica gel chromatography calcd for C78H119N3SO2 + H: 1162.9096; found 1162.9092.
hexanes : DCM (9 : 1 - 3 : 1) to yield a viscous yellow oil (0.6493 g,
1
Electrochemistry
55.7%). H NMR (400 MHz, CDCl3) d 7.34 (d, J = 8.9 Hz, 4H),
7.30–7.24 (m, 2H), 7.23 (d, J = 1.9 Hz, 2H), 6.75 (d, J = 8.5 Hz, 2H), Cyclic voltammetry (CV) experiments were carried out on an
6.57 (d, J = 9.0 Hz, 4H), 3.81 (t, J = 7.1 Hz, 2H), 3.36–3.20 (m, 8H), Autolab PGSTAT302 potentiostat that was controlled by a PC
1.86–1.73 (m, 2H), 1.64–1.53 (m, 8H), 1.48–1.38 (m, 2H), 1.38– running Autolab’s GPES v 4.9 software in a temperature- controlled,
1.21 (m, 68H), 0.95–0.86 (m, 15H). 13C NMR (101 MHz, CDCl3) three-electrode cell (15 mL). The working electrode was a Pt button,
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was a Pt wire. All potentials were referenced to the ferrocene/
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