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Page 1 of 15 Physical Chemistry Chemical Physics
DOI: 10.1039/C6CP01926A
Journal Name
ARTICLE
Synthesis,
photophysical,
electrochemical
and
electrochemiluminescent properties of A2B2 zinc porphyrins:
Received 00th January 20xx,
Accepted 00th January 20xx
effect of π–extended conjugation.
Elizabeth K. Galván-Miranda,a Hiram M. Castro-Cruz,a J. Arturo Arias-Orea,a Matteo Iurlo,b
DOI: 10.1039/x0xx00000x
Giovanni Valenti,b Massimo Marcaccio,b and Norma A. Macías-Ruvalcaba†a
Synthesis of two A2B2 porphyrins, {5,15-bis-[4-(octyloxy)phenyl]-porphyrinato}zinc (II) (4) and {5,15-bis-(carbazol-3-yl-
ethynyl)-10,20-bis-[4-(octyloxy)phenyl]-porphinato}-zinc (II) (9), is reported. The photophysical properties were studied by
steady-state absorption and emission. Substituting the carbazolylethynyl moieties at two of the meso positions results in a
large bathochromic shift of all the absorption bands, a notable increase on the absorption coefficient of the Q (0,0) band,
and higher fluorescence quantum yield compared to porphyrin 4, with two unsubstituted meso positions. Cyclic
voltammetry and digital simulation show that electrogenerated radical ions of 9 are more stable than those of 4. The lack
of substituents at the meso positions of 4 leads to dimerization reactions of the radical cation. Despite this, annihilation
reaction of 4 and 9 produces very similar electrogenerated chemiluminescence (ECL) intensity. Spectroelectrochemical
experiments demonstrate that the electroreduction of 9 leads to a strong absorption band that might quench the ECL.
properties, the incorporation of ethyne- or butadiyne- linkers
has proved very successful. This strategy has been used in the
synthesis of porphyrin-yne-porphyrin dimers, trimers or
Introduction
The potential applications of porphyrins have made them
attractive molecules in a wide range of research areas. They
have been used for the development of a broad variety of
sensors,1 as catalysts,2 in organic electronic devices,3 in dye
sensitized solar cells 4 and in bulk heterojunction cells,5 where
porphyrins are used for light harvesting as well as in energy
and electron transfer.
Most of these applications rely on their rich photophysical and
electrochemical properties, which can be fine-tuned by
different substitution patterns on the ring periphery,
incorporation of different metal ions in the core, or by axial
ligand coordination to the incorporated metal.6,7 It is known
that aromatic substituents directly appended on the meso-
positions of the porphyrin have little effect on the electronic
properties of the molecule because the steric interactions
oligomers,7,9,10
tetrakis(arylethynil)porphyrins,11
and
bis(arylethynyl)porphyrins (A2B2 and A2BC types).12–15
Bis(arylethynyl)porphyrins are particularly interesting for
organic photovoltaics, OLED’s development, and, in general,
the organic electronics field.14–17 As these applications usually
involve electron transfer reactions, the study of porphyrins
radical ion species is of major importance for this area.
Electrochemical techniques are powerful and versatile tools to
investigate the formation and stability of radical cations and
anions. The electrochemistry of porphyrins has been
extensively studied, they usually show two one-electron
oxidation and two one-electron reduction processes
corresponding to the formation of radical cation, dication,
radical anion, and dianion.18 These radical ion species are fairly
stable, especially in metallated porphyrins.9,10,19 Such stability,
along with their known emission properties, makes the
between the porphyrin
not allow for an efficient
achieve the extended conjugation of porphyrin molecules,
which translates into modification of their electronic
β
-hydrogens and the aromatic unit do
π
overlap between the two.8 To
porphyrins
ideal
candidates
for
electrogenerated
chemiluminescence (also called electrochemiluminescence,
ECL) studies.
Electrochemiluminescence arises from electron-transfer
reactions of radical ion or ionic species generated at electrode
surfaces; such reactions produce excited state molecules that
emit light.20 In the past few years, ECL applications and
processes, including the mechanisms through which it takes
place, have been reviewed;21–23 yet, the investigation of some
fundamental aspects, such as the correlation between
structure and ECL properties, are still an active issue.24
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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