Inorganica Chimica Acta
Nanosecond transient absorption spectroscopy of a Ru polypyridine
phenothiazine dyad
Gilbert K. Kosgei a,b, , Maksim Y. Livshits , Theodore R. Canterbury , Jeffery J. Rack , Karen J. Brewer a
⇑
b
a
b,
⇑
a
Department of Chemistry, Virginia Tech, Blacksburg, VA 24061-0212, United States
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131-0001, United States
b
a r t i c l e i n f o
a b s t r a c t
2
+
Article history:
A
bipyridine phenothiazine ligand [(PTZEtv bpy) and metal complexes [Ru(Ph phen) ]
(1),
2
2
3
Received 14 January 2016
Received in revised form 25 March 2016
Accepted 30 March 2016
Available online xxxx
2+
2+
[(Ph
2
phen)
2
Ru(PTZEtv
2
bpy)] (2), and [(PTZEtv
2
bpy)(Ph
2
phen)Ru(dpp)] (3) were synthesized and char-
phen is 4,7-diphenyl-1,10-phenanthroline, dpp is 2,3-bis(2-pyridyl)pyrazine and
bpy is 4,4 ethylene bridged phenothiazine 2,2 bipyridine. The reduction potentials of
bpy, 1, 2, and 3 were determined by cyclic and square wave voltammetric methods. The absor-
acterized, where Ph
PTZEtv
PTZEtv
2
0
0
2
2
bance and emission spectra of complexes 2 and 3 yield intense, visible Metal-to-Ligand Charge
Keywords:
Ruthenium
Polypyridene
Phenothiazine
Transient absorption
Transfer (MLCT) transitions. The nanosecond transient absorption data indicate formation of both the
3
3
MLCT state and a ligand localized PTZ state.
Ó 2016 Published by Elsevier B.V.
0
0
1
. Introduction
Phenothiazine moieties have previously been attached to ancil-
bromination of 4,4 -dimethyl-2,2 -bipyridine with N-bromo suc-
cinimide (NBS) [20]. The aldehyde PTZEt-CHO was prepared by
the Vilsmeier–Haack reaction with N-ethyl phenothiazine (PTZEt)
[4]. Similarly, the ruthenium complexes were prepared according
to published literature methods [14]. Complex 2 was synthesized
lary ligands of bipyridines, terpyridine and phenanthroline via a
non-conjugated or a pi-conjugated spacer/bridge [1–4]. The ruthe-
nium complexes of such ligands formed Donor–Chromophore–
Acceptor assemblies that create separated electron hole pairs for
subsequent chemistry [1,5–11]. Such assemblies, either as dyads
or triads, have been employed for photoinduced electron/energy
transfer [2–6] complexes for solar fuel generation [12–18]. One
advantage of phenothiazine is the variable attachment sites to
the assembly that may occur through one of the peripheral aro-
matic rings, the N-atom, or the S-atom [1–4,19]. Herein, we report
the spectral, electrochemical, and nanosecond transient absorption
data of a ruthenium polypyridine dyad comprising phenothiazine
with a conjugated linker.
in a one-pot reaction with [Ru(benzene)Cl
rial followed by sequential addition of PTZEtv
ligands, respectively [5]. In contrast, complex 3 was prepared in
2
]
2
as the starting mate-
2
bpy and Ph phen
2
a
multi-step reaction of [Ru(benzene)Cl
phen and dpp, in which the intermediates, [Ru(benzene)
bpy)Cl]Cl, and [Ru(PTZEtv bpy)(Ph phen)Cl ], were
2 2 2
] and PTZEtv bpy,
Ph
2
(PTZEtv
2
2
2
2
isolated and purified prior to subsequent reaction to produce
complex 3. Complexes 1, 2, and 3 were purified by column
chromatography. Additional synthetic details are found in the
Supporting information.
3
. Electrochemical properties
2
. Results and discussion
2
The reduction potentials of PTZEtv bpy, 1, 2, and 3 were deter-
mined by cyclic and square wave voltammetric methods and are
summarized in Table 1. The voltammograms of uncoordinated
The bipyridine phenothiazine ligand and metal complexes
employed in this work are shown in Fig. 1. The PTZEtv bpy ligand
2
was prepared via Wittig-Horner coupling of bipyridine di-phos-
phonate with the aldehyde, PTZEt-CHO [4]. The phosphonate was
prepared by the Michaelis–Arbuzov reaction with 4,4’-bis(bro-
PTZEtv bpy, 2, and 3 reveal a reversible couple at ꢀ+0.75 V versus
2
Ag/AgCl, which is accordingly assigned to oxidation of phenoth-
iazine. This assignment is consistent with literature values of phe-
nothiazine ruthenium polypyridine conjugates [1,2]. These data
indicate that the ethyl linkage bridging phenothiazine to
ruthenium does not alter the electronic properties of phenoth-
0
momethyl)-2,2 -bipyridine, which was previously formed by
⇑
Corresponding authors at: Department of Chemistry and Chemical Biology,
University of New Mexico, Albuquerque, NM 87131-0001, United States.
3
+/2+
iazine. We observe the Ru
reduction potential near +1.25 V
0
020-1693/Ó 2016 Published by Elsevier B.V.