Synthesis , Characterization , Electrochemistry , and Spectroscopic Properties of Some Anthracenyl Functionalized Phthalocyanine Complexes of Ruthenium ( II )

The synthesis of singleand double-decked anthracenyl functionalized ruthenium(II) phthalocyanine complexes has been achieved through a controlled electrophilic aromatic substitution reaction of the free unsubstituted ruthenium(II) phthalocyanine with preformed 9-bromo-10-(2,3-dimethylacrylic acid)-anthracene and/or 9-bromo-10-(2,3-dimethylacrylic acid)-dianthracene using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalyst.The complexes were characterized by IR, UV-Vis, fluorescence, H, CNMR, and elemental analyses. A dimeric complex (C3R󸀠󸀠RuPc, where R is 9-dianthracenyl-10-(2,3-dimethylacrylic acid), obtained as the major product of the dianthracenyl-substituted ruthenium phthalocyanine complex displays a strong near-infrared visible absorption band wavelength maxima at 1027 nm (ε = 5.47×10M cm), with an interesting photoluminescent and electroredox active properties.


Introduction
Phthalocyanines (Pcs) are a widely studied class of organic chromophores [1].They have proved useful for a variety of applications ranging from molecular electronic to medicine [2].Their utility derives, in part, from the ease with which their properties can be modified through synthetic manipulation.Syntheses of new Pcs typically concentrate on a combination of modifications of the benzenoid substituents and variation of the central metal ion.With regard to metal ion insertion, attention has focused most extensively on metal(II) and metal(III) derivatives, the latter providing a further site for incorporation of a substituent as an axial ligand [1].
In general, metallated phthalocyanines are prepared by two methods: (i) cyclotetramerisation of a phthalic acid derivative (such as a phthalonitrile or diiminoisoindoline) in the presence of a metal salt and (ii) insertion of the desired metal ion into the preformed phthalocyanine ring either as its metal-free or dilithiated derivative [3][4][5][6].The more commonly used method for the preparation of ruthenium phthalocyanine derivatives has tended to be the former and the two ruthenium reagents frequently used for the synthesis of ruthenium phthalocyanines are RuCl 3 and [Ru 3 (CO) 12 ] [7,8].Introduction of substituents into the precursors such as phthalonitriles and final condensation to Pcs are common synthetic routes of which MPc with interesting photochemical and photophysical characteristics being made.Despite this, a precursor with specified substituents is not always readily available or, in other instances, hard to condense to Pc [9,10].In this situation, introducing substituents to Pc directly instead of introducing them to the precursor is needed.However, direct substitution of the Pc ring often results in mixtures [11].One method to reduce position indeterminacy is displacement of a group readily introduced to a precursor which is easy to condense to Pc.

Experimental
2.1.Material.All chemical and reagents were analytically pure and used without further purification.9-Anthracenyl-10-(2,3-dimethylacrylic acid) and 9-dianthracenyl-10-(2,3dimethylacrylic acid) were synthesized as described in the literature [14].The ruthenium(II) phthalocyanine complexes were synthesized as reported in the literature with slight modifications [16].All thin layer chromatography (tlc) analyses were done with aluminum sheet precoated with normal phase silica gel 60 F 254 (Merck, 0.20 mm thickness), except otherwise stated.The tlc plates were developed using any of the following solvent systems.

Equipment.
Melting points were determined using Gallenkamp electrothermal melting point apparatus.Microanalyses (C, H, N) were carried out with a Fisons elemental analyser and infrared spectra were obtained with KBr discs or nujol on a Perkin Elmer System 2000 FT-IR spectrophotometer.UV-Vis and fluorescence spectra were recorded in 1 cm path length quartz cell on a Perkin Elmer Lambda 35 spectrophotometer and Perkin Elmer Lambda 45 spectrofluorometer, respectively. 1H and 13 C Nuclear Magnetic Resonance spectra were run on a Bruker EMX 400 MHz spectrometer for 1 H and 100 MHz for 13 C.The chemical shift values were reported in parts per million (ppm) relative to TMS as internal standard.Chemical shifts were also reported with respect to CDCl 3 at  c 77.00 and  H CDCl 3 at 7.25 and DMSO d 6 at  c 40.98 and DMSO d 6 at  H 2.50 for synthesized ligands and complexes.All electrochemical experiments were performed using Autolab potentiostat PGSTAT 302 (Eco-Chemie, Utrecht, The Netherlands) driven by the general purpose Electrochemical System data processing software (GPES, software version 4.9).A conventional three-electrode system was used.The working electrode was a bare glassy carbon electrode (GCE), and Ag|AgCl wire and platinum wire were used as the pseudoreference and auxiliary electrodes, respectively.The potential response of the Ag|AgCl pseudoreference electrode was less than the Ag|AgCl (3M KCl) by 0.015 ± 0.003 V. Prior to use, the electrode surface was polished with alumina on a Buehler felt pad and rinsed with excess millipore water.All electrochemical experiments were performed in freshly distilled dry DMF containing TBABF 4 as supporting electrolyte.

Results and Discussion
3.1.Synthesis.The preparation of phthalocyanines relies on the availability of the precursor phthalonitriles which undergo cyclotetramerization to form the macrocycles [17,18].It is to be noted that a direct palladium catalyzed cross-coupling reaction of functionalized bromoanthracenyl derivatives with bromophthalonitrile to form anthracenyl phthalonitrile prior to condensation to phthalocyanine was not successful.However, Lin Mei-jin and coworkers [16] reported a convenient synthesis of a substituted phthalocyanine compounds using bromosubstituted phthalonitrile as precursor followed by a nucleophilic substitution reaction of the bromogroup.A reverse synthetic procedure in which bromofunctionalized anthracene derivatives were reacted directly in an electrophilic aromatic substitution of the protons of the free ruthenium phthalocyanine afforded the desired products (Scheme 1).The reaction of ruthenium phthalocyanine (RuPc) with either 9-bromo-10-(2,3dimethylacrylic acid)-anthracene and/or 9-bromo-10-(2,3dimethylacrylic acid)-dianthracene gave two products each after column chromatography.On the other hand, no Q-band absorption value was obtained for the product with singlelinked anthracenyl RuPc.

Infrared Spectra.
The infrared spectra of the two functionalized anthracenyl ruthenium(II) phthalocyanines were carefully compared with the unsubstituted ruthenium(II) phthalocyanine precursor and bands were assigned accordingly.A strong OH vibrational stretch characteristic of , unsaturated carboxylic acid was found as a broad band at 3413 cm −1 for both mono-and dianthracenyl derivatives.This band was shifted to lower frequency (ca.195 cm −1 , 21 cm −1 , and 96 cm −1 ), respectively, for (C 1 R  RuPc, C 2 R  RuPc, and C 3 R  RuPc).Common to the anthracenyl ligands and the complexes were two stretching vibrational bands between 3081 and 2857 cm −1 that were assigned to the methyl groups in the molecules.The infrared spectra of complexes with axial carbonyl ligands have characteristic bands in the region 1922-1965 cm −1 assigned to ](C-O) [19][20][21].Bands at 1688, 1642, and 1321 cm −1 were unambiguously assigned to the ](C=O) and ](C-O) stretching of carboxylic acid groups in the complexes.The bands in the regions 1642 and 1441 cm −1 contain contributions mostly from the atoms in the pc rings near to the metal; these peaks have been found to be sensitive to the central metal atom [22].It is well known that different polymorphic organizations of phthalocyanines also show different IR absorbance patterns which can be useful in identifying and characterizing a particular form or dimorphic transition.In particular, in the range between 800 and 700 cm −1 , the out-of-plane C-H bending vibrations are expected.In fact, due to the sensitivity of these vibrations to the molecular packing, the major differences reported so far for both metallated phthalocyanines and the free ligand of different polymorphic structures were discovered in this range [23].As can be seen, the spectra are very similar in the shown range, but, in the above-mentioned region, some differences can be noticed: the three-band system is constituted in (C 1 R  RuPc) by well-defined bands at 732, 741, and 744 cm −1 , while, in (C 2 R  RuPc), the first one is centered at 728 cm −1 with a pronounced shoulder at 754 cm −1 and, in the third, (C 3 R  RuPc) is found at 742, 723, and 758 cm −1 with a shoulder at 719 cm −1 .In the neighborhood of 900-960 cm −1 , a strong sharp peak was observed in (C 3 R  RuPc) which was conspicuously absent in (C 1 R  RuPc) and (C 2 R  RuPc).At this region, one can notice the disappearance and/or a low absorbance in the latter complexes, which can be attributed to different molecular packing in the molecules.These small differences in the IR spectra could well support the differences attributed to the complexes in the optical spectra reported below.

UV-Vis Absorption and Emission Spectra.
The electronic spectra of ruthenium phthalocyanines (C 1 R  RuPc), (C 2 R  RuPc), and (C 3 R  RuPc) show the Q bands of a typical macrocycle substituted Pc [24][25][26].The energy level location corresponding to this band is illustrated in (Figure 1).In the UV-region, anthracene displays strong absorptions between 300 and 400 nm in the solution, with pronounced vibronic peaks at 331, 350, 369, and 388 nm characteristic of anthracene derivatives and with highest molar absorptivity coefficient recorded for C 1 R  RuPc [27].The presence of these bands is thought to have overlapped the weak Soret band which normally appears in the region 340-385 nm and attributed to a charge transfer (CT) transition [4,25,26].
In the visible region, (C 1 R  RuPc) and (C 2 R  RuPc) showed single-broad Q-bands (633, 618 nm) with accompanied weak shoulder bands at 573 and 566 nm, respectively.The Q-band splitted into two (620 and 631 nm) in (C 3 R  RuPc) with corresponding weak shoulder band at 561 nm.These absorptions were assigned to  →  * transition within the macrocycle [7].
Coordination of a carbonyl ligand induces a bathochromic shift of 300-500 cm −1 and a significant increase in  the molar absorptivity [20].The splitting of Q-band as found in (C 3 R  RuPc) may be adduced to the new steric and symmetrical properties imposed on the complex by solvation of the phthalocyanine and axial ligands and the polar electronic influence of the solvents on the ligands.Peripheral substitution of the macrocycle has only a weak influence on the position of the Q-band.Hanack group reported that peripheral substitution with an electron-donating group causes a weak bathochromic shift of the Q-band [28].The near-infrared absorption band in (C 3 R  RuPc) was attributed to a better -bond conjugation indicative of the synergy effect of the Ru-Ru metal bond linkage of the dimeric complex.The (C 1 R  RuPc), (C 2 R  RuPc), and (C 3 R  RuPc) complexes exhibit intense and long-lived orange-red lumine-FH RuPc 100, CDCl 3 , zg30:    anthracene units in the aromatic region are well resolved and appear as doublet of doublet peaks at chemical shift values at  7.47, 7.50, and 8.09 ppm, respectively.In addition, the macrocyclic Pc ring protons were found as doublet at  8.01 ppm and a singlet at  8.43 ppm for (C 1 R  RuPc) typical of AAAA-type coupling pattern, while an ABBB-type in (C 3 R  RuPc) could be ascribed to the proton singlet peaks at 9.12, 8.55, 8.33, and 7.96 ppm [31].The aliphatic region of the complexes (C 1 R  RuPc) and (C 3 R  RuPc) rather presents unstructured signals between 2.93 and 2.17 ppm.However, the methyl groups of the 2,3-dimethylacrylic acid moiety are strong and well resolved.The methyl groups increase the solubility and stability properties of the complexes.
In the 13 C-NMR spectra of (C 1 R  RuPc) and (C 3 R  RuPc) (Figures 5 and 6), there are characteristic signals for the axial coordinated carbonyl groups which appear at 166.04 ppm for (C 1 R  RuPc) and 175.43 ppm for (C 3 R  RuPc).The downfield shift may be ascribed to the steric hindrance in the dimer molecule.The extension of the -conjugated bond as a result of the doubly linked anthracene and the dimeric nature of (C 3 R  RuPc) complex appeared to have synergistic effects when compared to a monomeric anthracenyl substitution in   2+ species [32,33].Oneelectron reduction process was observed in the two complexes at −0.71 V and was assigned to reduction of the macrocycle and/or the anthracene unit [34].The difference of ∼2 V between the first reduction and oxidation processes appears typical for this type of complex [20,34].When compared to complexes of the type [Pc 0 Ru II L 2 ] 2+ (where L is N-donor ligands), the presence of CO always shows only one oxidation process at more positive potentials which may be expected due to greater -back bonding of the ligated CO complexes [33]  the electron-donor nature of the anthracene molecular unit is not excluded [34].

Conclusion
In summary, 9-bromo-10-(2,3-dimethylacrylic acid) anthracene and 9-bromo-10-(2,3-dimethylacrylic acid) dianthracene reacted conveniently with a nonsubstituted ruthenium phthalocyanine in an electrophilic aromatic substitution reaction.This route may be useful in some syntheses of substituted MPc, where the condensation reaction by the precursor bearing the target substitution group is difficult.The photophysical and electrochemical properties exhibited by (C 1 R  RuPc), (C 2 R  RuPc), and (C 3 R  RuPc) complexes make them suitable as potential materials for molecular electronic devices, most especially their use as sensitizers for dye-sensitized solar cells (DSSCs).The (C 3 R  RuPc) complex due to its near-infrared absorption property could also serve as carrier generation material.

Figure 5 :
Figure 5: (a) 13 C NMR spectrum of C 3 R  RuPc.(b) Aromatic region of 13 C NMR spectrum of C 3 R  RuPc.

Figure 6 :
Figure 6: Aromatic region of 13 C NMR spectrum of C 1 R  RuPc.

Plate 1 :Plate 2 :
. The dimeric complex (C 3 R  RuPc) (Plate 2) displays somewhat different redox behaviour to monomeric complexes (C 1 R  RuPc) and (C 2 R  RuPc).(C 3 R  RuPc) undergoes centered oxidation, although the possibility of ringbased oxidation is also possible.The reduction process is attributed to either the addition of electrons into metal d( * ) orbitals giving Ru 1 -Ru 1 species or the electron reduction of the phthalocyanine macrocycle.The possibility of this to Potential (V) versus Ag|AgCl (a) C 1 R  RuPc (b) C 2 R  RuPc CVs of C 1 R  RuPc and C 2 R  RuPc CV of C 3 R  RuPc