Charge-Transfer and Energy-Transfer Processes in π-Conjugated Oligomers and Polymers: A Molecular Picture

Light-Emitting Self-Assembled Materials Based on d(8) and d(10) Transition Metal Complexes.

The synthesis and structural, photophysical, electrochemical, and electroluminescent properties of a class of platinum(II) complexes bearing σ-alkynyl ancillary ligands, namely [(C∧N∧N)Pt(C⋮C)nR] [H(C∧N∧N) = 6-aryl-2,2‘-bipyridine; n = 1−4; R = aryl, alkyl, or trimethylsilyl], have been studied. Substituents with different steric and electronic properties were introduced into the tridentate cyclometalating and arylacetylide ligands, and the π-conjugation length of the oligoynyl moiety was homologously extended from ethynyl to octatetraynyl. The X-ray crystal structures of several derivatives confirm the Pt−(C⋮C) ligation and reveal various intermolecular interactions, such as π−π, Pt···Pt, and C−H···F−C. The complexes display good thermal stability and intense phosphorescence in fluid and glassy solutions with high quantum yields and microsecond lifetimes. Their emission energies are sensitive to solvent polarity, the electronic affinities of the substituents on both the cyclometalating and arylacetylide ...

Light-Emitting Tridentate Cyclometalated Platinum(II) Complexes Containing σ-Alkynyl Auxiliaries: Tuning of Photo- and Electrophosphorescence

Bulk heterojunction solar cells have been extensively studied owing to their great potential for cost-effective photovoltaic devices. Although recent advances resulted in the fabrication of poly(3-hexylthiophene) (P3HT)/fullerene derivative based solar cells with efficiencies in the range 4.4-5.0%, theoretical calculations predict that the development of novel donor materials with a lower bandgap is required to exceed the power-conversion efficiency of 10%. However, all of the lower bandgap polymers developed so far have failed to reach the efficiency of P3HT-based cells. To address this issue, we synthesized a soluble, intensely coloured platinum metallopolyyne with a low bandgap of 1.85 eV. The solar cells, containing metallopolyyne/fullerene derivative blends as the photoactive material, showed a power-conversion efficiency with an average of 4.1%, without annealing or the use of spacer layers needed to achieve comparable efficiency with P3HT. This clearly demonstrates the potential of metallated conjugated polymers for efficient photovoltaic devices.

Metallated conjugated polymers as a new avenue towards high-efficiency polymer solar cells

Today's technology is not possible without optoelectronic devices such as light-emitting diodes, transistors and solar cells. These basic units of modern electronic appliances may be made not only from traditional inorganic semiconductors, but also from organic semiconductors, i.e. hydrocarbon molecules that combine semiconducting properties with some mechanical properties such as easy processability and flexibility. The weak van der Waals forces that bind the molecules to a solid imply a low dielectric constant, so that coulomb and exchange interactions between electrons are significant. As a result, photoexcitation or electrical excitation results in strongly bound electron–hole pairs, so-called excitons. Depending on the relative orientation of the electron and hole spin, the exciton may be of a overall singlet or triplet spin state. While the fluorescent singlet state has been investigated intensively since the first reports of organic electroluminescence, research into the properties of the phosphorescent triplet state has intensified mainly during the last decade. In this review we give an overview on the photophysical processes associated with the formation of triplet states and their decay, as well as the energy levels and energy transfer processes of triplet states. We aim to give a careful introduction for those new to this particular research area as well as to highlight some of the current research issues and intriguing questions for those familiar with the field. The main focus of this review is on molecular assemblies and polymer films, though relevant work on molecular crystals is also included where it assists in forming a larger picture.

Triplet states in organic semiconductors

Soluble, rigid-rod organometallic polymers trans-[-Pt(PBu3n)2–C≡C–R–C≡C–]∞ (R=bithienyl 2, terthienyl 3) have been synthesized in good yields by the CuI-catalyzed dehydrohalogenation reaction of trans-[Pt(PBu3n)2Cl2] with one equivalent of the diterminal alkynyl oligothiophenes H–C≡C–R–C≡C–H in CH2Cl2/iPr2NH at room temperature. We report the thermal properties, and the optical absorption, photoluminescence, and photocurrent action spectra of 1 (trans-[–Pt(PBu3n)2–C≡C–R–C≡C–]∞, R=thienyl), 2 and 3 as a function of the number of thiophene rings within the bridging ligand. With increasing thiophene content, the optical gap is reduced and the vibronic structure of the singlet emission changes toward that typical for oligothiophenes. We also find the intersystem crossing from the singlet excited state to the triplet excited state to become reduced, while the singlet–triplet energy gap remains unaltered. The latter implies that, in these systems, the T1 triplet excited state is extended over several thiophene ...

Evolution of lowest singlet and triplet excited states with number of thienyl rings in platinum poly-ynes

A series of 1,4-diethynylbenzene (1) derivatives, H–CC–R–CC–H with R=C6H3NH2
(2), C6H3F (3), C6H2F2-2,5 (4), C6F4
(5), C6H2(OCH3)2-2,5 (6) and C6H2(OnC8H17)2-2,5 (7) has been synthesised and their crystal structures determined by single crystal (2–5) or powder (6, 7) X-ray diffraction. The CCH⋯πCC hydrogen bonds dominating structure 1 are gradually replaced by CC–H⋯F ones with the increase of fluorination (3→5), or completely replaced by CCH⋯N and NH⋯πCC bonds in 2, and CCH⋯O in 6 and 7. The related platinum-based polymers, trans-[–Pt(PnBu3)2–CC–R–CC–]n
(R=as above and C6H4,) have been prepared and characterised by spectroscopic methods and thermogravimetry, which show that the amino- and methoxy-derivatives have lowest thermal stability while the fluorinated ones exhibit increasing thermal stability with increasing fluorination. Optical spectroscopic measurements reveal that substituents on the aromatic spacer group do not create strong donor–acceptor interactions along the rigid backbone of the organometallic polymers.

Synthesis and optical characterisation of platinum(II) poly-yne polymers incorporating substituted 1,4-diethynylbenzene derivatives and an investigation of the intermolecular interactions in the diethynylbenzene molecular precursors

Timothy C. Corcoran

Papers

Evolution of lowest singlet and triplet excited states with number of thienyl rings in platinum poly-ynes

Synthesis and optical characterisation of platinum(II) poly-yne polymers incorporating substituted 1,4-diethynylbenzene derivatives and an investigation of the intermolecular interactions in the diethynylbenzene molecular precursors

Properties of Omani artificial pozzolana (sarooj)