Synthesis, characterization, photophysical and photovoltaic properties of new donor–acceptor platinum(II) acetylide complexes

doi:10.1016/j.jorganchem.2015.06.017

Journal of Organometallic Chemistry

Volume 812, 15 June 2016, Pages 2-12

https://doi.org/10.1016/j.jorganchem.2015.06.017 Get rights and content

Highlights

•
New platinum(II) acetylide donor-acceptor (D–A) triads were prepared.
•
Spectroscopic, redox and structural characterization were carried out.
•
Bulk heterojunction solar cells using these platinum complexes were fabricated.

Abstract

Six new solution processable platinum(II) acetylide donor-acceptor (D-A) triads end-capped by 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) have been synthesized and characterized by photophysical and electrochemical methods. All these materials possess low bandgaps and strong UV/Vis absorption between 400 and 700 nm. Bulk heterojunction (BHJ) solar cells based on these molecules as donor materials were fabricated. The best power conversion efficiency (PCE) of 1.46% with the open-circuit voltage (V_oc) of 0.70 V, short-circuit current density (J_sc) of 6.17 mA cm⁻² and fill factor (FF) of 0.33 was achieved under illumination of an AM 1.5 solar cell simulator. These results suggest the potential use of solution-processable small molecular platinum(II)-acetylides for efficient generation in organic photovoltaic implementation.

Graphical abstract

Six new solution-processable platinum(II) acetylide donor-acceptor (D-A) triads end-capped y 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) were synthesized and characterized by photophysical and electrochemical methods. These compounds were also used as active layers in the fabrication of organic solar cells.

Introduction

Recently, more attention has been paid to the energy crisis and environmental protection. Renewable energy sources have become a hot topic in the research community [1], [2]. Among these organic solar cells (OSCs) have attracted much interest owing to their advantages over traditional silicon based solar cells, including solution processability, flexibility, lightweight and large-area fabrication at low cost [3]. Therefore, many related research activities are now focusing on developing new photovoltaic materials and optimizing these device architectures [4], [5], [6]. Great progress has been made in the field of organic bulk heterojunction (BHJ) solar cells since its inception in 1995 [7]. BHJ solar cells comprise of donor-acceptor (D-A) systems which typically contain electron-donating materials and electron-withdrawing fullerene derivatives. Since then, significant improvements on power conversion efficiencies (PCEs) were achieved by alternating the device structures and modifying the structures of donor materials. The PCEs of single BHJ solar cells near 10% have been achieved for polymer-based solar cells (PSCs) [8], [9] and small molecule-based solar cells (SMSCs) [10], [11], [12], respectively. In contrast to the polymeric system, small molecules employed for SMSCs are easier to be synthesized and purified as they possess well-defined structures. Although the PCEs of SMSCs are still slightly behind those of PSCs, the large structural variations in the molecular weight, polydispersity, and regioregularity in polymeric systems result in poor reproducibility of PCEs [13], [14], [15], [16].

Platinum(II)-containing polyynes and their oligomers have been demonstrated to be useful in photovoltaic applications [17], [18], [19], [20], [21], [22], [23]. Solution-processable polymeric semiconductors with Pt(II) centers possessing D-A architecture in the backbone were shown to exhibit broad absorption bands due to the intramolecular charge transfer (ICT) between the donor and acceptor units and small bandgaps which are suitable for photovoltaic devices [24]. The complexation of an electron-rich platinum(II) ion with the conjugated chain was reported to enhance the intrachain charge transport of π-conjugated polymers [25]. To get rid of the uncertainty in PCE induced by polymeric materials, here we report the utility of molecular Pt(II) complexes with different electron-donating groups and electron-accepting di-2-thienyl-2,1,3-benzothiadiazole (DTBT) unit that can modify the ICT strength of the D-A component for BHJ solar cell applications. Oligothiophene component was employed to fine-tune the ICT strength of the D-A component within the system. These complexes can be synthesized easily in high purity. Their optical, electronic and photovoltaic properties have been studied and their structure-photovoltaic property relationships with different spacers will be presented.

Section snippets

Synthesis and characterization

Compounds L1-2Br–L6-2Br were prepared according to the procedures reported in the literature [26], [27], [28], [29], [30], [31]. The synthetic routes for the preparation of the diethynyl ligands L1–L6 and a new series of bi(thienyl)benzothiadiazole end-capped platinum(II)-acetylide compounds PT1–PT6 are illustrated in Scheme 1. The trimethylsilylacetylenic compounds L1-2TMS–L4-2TMS were synthesized by the Sonogashira reaction between L1-2Br–L6-2Br and trimethylsilylacetylene under Pd(OAc)₂, CuI

Conclusions

A new series of platinum(II) acetylide donor-acceptor triads PT1–PT6 which were end-capped by 4,7-di-2-thienyl-2,1,3-benzothiadiazole have been successfully designed and prepared by convenient synthetic processes with reasonably good yields. These platinum(II) containing complexes were characterized by photophysical and electrochemical methods. The absorption profile of these metal complexes is significantly broadened by the D−A motif, which leads to the enhancement of the overlap for the

Materials and reagents

All manipulations were performed by using Schlenk techniques under dry nitrogen atmosphere. Solvents were dried by the standard methods and distilled prior to use except for those of spectroscopic grade for photophysical and electrochemical measurements.

Physical measurements

NMR spectra were measured in deuterated solvents as the lock and reference on a Bruker AV 400 instrument. Chemical shifts are given relative to tetramethylsilane for ¹H and ¹³C NMR data and 85% H₃PO₄ (external standard) for ³¹P NMR data.

Acknowledgments

We thank the National Natural Science Foundation of China (project number 51373145), Areas of Excellence Scheme, University Grants Committee of HKSAR (project No. AoE/P-03/08), Hong Kong Baptist University (FRG2/13-14/083), Hong Kong Research Grants Council (HKBU203312) and the Science, Technology and Innovation Committee of Shenzhen Municipality (JCYJ20140419130507116) for financial support. The work was also supported by Partner State Key Laboratory of Environmental and Biological Analysis (

References (39)

S.C. Roy et al.
ACS Nano
(2010)
J.A. Turner
Science
(1999)
A. Mishra et al.
Angew. Chem. Int. Ed.
(2011)
C.E. Small et al.
Nat. Photonics
(2012)
X.H. Li et al.
Adv. Mater.
(2012)
J. Warnan et al.
Adv. Mater.
(2014)
G. Yu et al.
Science
(1995)
C. Liu et al.
ACS Appl. Mater. Interfaces
(2015)
L. Huo et al.
Adv. Mater.
(2015)
B. Kan et al.
J. Am. Chem. Soc.
(2014)

J. Zhou et al.

J. Am. Chem. Soc.

(2013)

Y. Chen et al.

Acc. Chem. Res.

(2013)

Z.B. Henson et al.

Nat. Chem.

(2012)

J.A. Bartelt et al.

Adv. Energy Mater.

(2014)

Y.Z. Lin et al.

Chem. Soc. Rev.

(2012)

L.S. Li et al.

J. Mater. Chem. C

(2014)

W.-Y. Wong et al.

Nat. Mater.

(2007)

L. Liu et al.

Adv. Funct. Mater.

(2008)

A. Ng et al.

Macromol. Chem. Phys.

(2012)

Cited by (14)

Platinum(II)-containing donor-acceptor dimesitylborane-based complexes: Synthesis, characterization, photophysical and photovoltaic properties
2022, Journal of Organometallic Chemistry
Citation Excerpt :
Generally, the methods for preparing the new platinum(II) acetylide complexes PT1−PT4 and their corresponding ligands L1−L4 are outlined in Schemes 1. The key compounds L1−2Br and Pt-1 were prepared according to the literature methods [30,31]. In the synthesis of dimesitylborane-based conjugated oligothiophene-bridged compounds PT1−PT4, the dibromo precursors (L2−2Br, L3−2Br, and L4−2Br) can be obtained from L1−2Br by successive coupling of 2-thienylboronic acid bromide with the corresponding dibromide of the lower generation.
A new series of platinum(II)-containing donor-acceptor (D-A) dimesitylborane-based complexes PT1−PT4 have been successfully synthesized in reasonable yields. The photophysical and electrochemical properties have also been investigated. Complexes PT1−PT4 have narrow energy bandgaps within 1.69−1.74 eV and broad absorption bands within 240−700 nm, which would be suitable candidates for the fabrication of devices in bulk heterojunction (BHJ) solar cells. The devices based on PT4, which has the longest π-conjugated framework, showed the highest PCE of 3.07% among all the devices with high open-circuit voltage (V_oc) of 0.92 V, short-circuit photocurrent density (J_sc) of 7.95 mA cm⁻² and fill factor (FF) of 0.42 at the optimized active layer thickness of 85 nm. These complexes illustrate the potential of solution-processible metallo-organic D-A complexes for efficient power generation in photovoltaic implementation.
Binuclear organometallic Pt(II) complexes as stabilizing ligands for gold and silver metal nanoparticles
2021, Inorganica Chimica Acta
Citation Excerpt :
The trans-stilbene organic bridge allows for an extension of the conjugated carbon chain with respect to its biphenyl analog, while the alkyl chains in the 9-position of the fluorene system are expected to bring improved solubility of both complex and MNPs in organic solvents, thus extending the array of tunable properties of such systems. These ligands are characterized by an extended π-system that can enhance the plasmon resonance effect of the linked nanoparticles and introduce specific absorption and emission optical features in the MNPs [30–32]. Furthermore, their bifunctional structure allows the formation of an interconnected system of nanoparticles with extensive delocalization of the electrical charge.
The bifunctional hybrid thioester ligands containing square planar Pt(II) centers 2,7-bis[2-(trans-acetylthio-bis-(tributylphosphine)platinum^II)ethynyl]-9,9-didodecyl-9H-fluorene (1) and trans-4,4′-bis[2-(trans-acetylthio-bis-(tributylphosphine)platinum^II)ethynyl]stilbene (2) have been prepared in a four-step procedure and used as stabilizing and interconnecting ligands for gold and silver nanoparticles (MNPs), formed in-situ upon deacylation of the MeCOS-Pt(II)-terminal groups. The metallic surface is linked to the Pt(II) centers of the ligands via M-S-Pt(II) bridges. The size of the AuNPs and AgNPs which aggregate into a bi-dimensional network through hybrid metal-organic bridges was controlled by careful choice of synthetic parameters. The morpho-structural features of the nanoparticles, investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS), highlighted the linkage between the nanoparticles, featuring diameters below 10 nm.
Platinum emitters with dye-based σ-aryl ligands
2019, Coordination Chemistry Reviews
Citation Excerpt :
Combinations of an ethynylated naphthalimide and a coumarin [138] or a pyrene [155], a bodipy and a naphthalene diimide [156,157] or a rhodamine [158], a naphthalimide and a phenothiazine, or a tetracene and a pentacene [159] were realized and scrutinized for their photophysical properties [160]. This concept was also extended to di- or triplatinum complexes with terminal and bridging ethynylbodipys [161,162], benzothiadiazoles and diketopyrrolopyrroles, benzotriazoles, 4,8-dialkoxy-benzo[1,2-b:4,5-b’]dithiophenes, carbazoles or isoindigo [163], or complexes with one bridging diethynyl and two terminal ethynylated acenes with different degrees of anellation [164], as well as to tetraplatinum complexes with a central tetrakis(4-ethynylphenyl) or N,N,N’,N’-diboraazophenine and four peripheral ethynyltruxenes [165,166]. These complexes are, however, outside the focus of the present review and are therefore not further discussed here.
Attachment of a dye to a platinum-coligand entity via a direct Pt-C(aryl) σ-bond has a great impact on its photophysical properties. Apart from the trivial effect of altering the associated absorption and emission wavelengths, the close proximity to the heavy platinum ion with its large intrinsic spin-orbit coupling constant accelerates intersystem crossing (ISC). For many complexes, this effect is further augmented by charge-transfer contributions to certain absorption bands, which provides another, even more efficient pathway for promoting ISC according to the rule of El-Sayed. As an immediate consequence, the fluorescence emission of the free dye is often quenched. On the other hand, the same mechanisms also accelerate ISC from an excited triplet state to the ground state S₀. This switches on phosphorescence from the dye ligand, which is either absent in the free dye or can only be observed at low T, usually at 77 K. Depending on the balancing of the associated rate constants for the fluorescence emission, ISC from excited S_n states to the T manifold, as well as ISC from the T₁ state to the S₀ ground state, the complexes are either weakly fluorescent, or weak to very powerful phosphorescence, or dual fluorescence and phosphorescence emitters. In this review, we discuss the photophysical properties of complexes with mono-, bi-, or polydentate ligands, which contain at least one dye, which attaches to the platinum(II) ion via a direct platinum-aryl bond. We also discuss relevant work on bichromophoric complexes with two dye ligands and the additional prospects of energy transfer from one dye ligand to the other, or of separate emissions from the different dyes.
Near-infrared absorbing metal functionalized diketopyrrolopyrroles
2017, Journal of Organometallic Chemistry
A symmetrical cobalt-dithiolene functionalized diketopyrrolopyrrole (DPP) Co-DPP-Co was designed and synthesized. Its photophysical, thermal, electrochemical and computational studies were compared with symmetrical ferrocenyl Fc-DPP-Fc. The electronic absorption spectrum of Co-DPP-Co exhibited absorption in Vis-NIR region with shoulder band in longer wavelength region. The thermogravimetric analysis shows good thermal stability of Co-DPP-Co. The density functional theory (DFT) investigation exhibited the cis geometry of cobalt-dithiolene ring with respect to DPP in Co-DPP-Co whereas trans geometry was observed for ferrocenyl unit in Fc-DPP-Fc.
Recent progress in organic-metal complexes for organic photovoltaic applications
2023, Materials Chemistry Frontiers
Charge Transfer Chromophores Derived from 3d-Row Transition Metal Complexes
2022, Molecules

View all citing articles on Scopus

View full text

Synthesis, characterization, photophysical and photovoltaic properties of new donor–acceptor platinum(II) acetylide complexes

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis and characterization

Conclusions

Materials and reagents

Physical measurements

Acknowledgments

ACS Nano

Science

Angew. Chem. Int. Ed.

Nat. Photonics

Adv. Mater.

Adv. Mater.

Science

ACS Appl. Mater. Interfaces

Adv. Mater.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

Acc. Chem. Res.

Nat. Chem.

Adv. Energy Mater.

Chem. Soc. Rev.

J. Mater. Chem. C

Nat. Mater.

Adv. Funct. Mater.

Macromol. Chem. Phys.