Design and synthesis of functionalized alkynylplatinum (II) polypyridyl complexes and oligothienylenevinylene derivatives : from dye-sensitized solar cells to bilayer heterojunction photovoltaics

Abstract

A series of alkynylplatinum(II) polypyridine complexes with

4,4′,4′′-tricarboxy-2,2′:6′,2′′-terpyridine and 4,4′-dicarboxy-2,2′-bipyridine as TiO2

anchoring functionalities, has been successfully synthesized. Their photophysical,

electrochemical and luminescence properties have been extensively studied. The

excited state properties were probed using nanosecond transient absorption

spectroscopy. [Pt(tctpy)(C≡C-Th-BTD-Th)][NnBu4]2 displayed a long-lived transient

signal which was tentatively assigned to result from the formation of a

charge-separated state, which could be alternatively described as a

[Pt(tctpy)???(C≡C-Th-BTD-Th)+?] state, with the charge recombination rate constant

determined to be 2.9 × 105 s?1. The excited state redox potentials for the oxidation

process were determined and the data confirmed the ability of the complexes to inject

an electron into the conduction band of TiO2. The majority of the complexes were

found to sensitize the nanocrystalline TiO2 and exhibit photovoltaic properties, which

have been characterized by current-voltage measurements under illumination of air

mass (AM) 1.5G sunlight (100 mW cm–2).

A new class of molecular dyads comprising metalloporphyrin-linked

alkynylplatinum(II) polypyridine complexes was synthesized and characterized. Their

photophysical, electrochemical and luminescence properties have been studied in

detail. The excited state properties were probed using nanosecond transient absorption

spectroscopy which indicated the formation of a charge-separated state involving the

porphyrin radical anion, [Por??－(C≡C)Pt+?]. The excited state redox potentials for the

oxidation process were also determined with the data supporting the capability of the

complexes to inject an electron into the conduction band of TiO2. The majority of the

complexes were found to sensitize the nanocrystalline TiO2 and exhibit photovoltaic

properties, as characterized by current-voltage measurements under illumination of air

mass (AM) 1.5G sunlight (100 mW cm–2).

A series of organic materials consisting of a triphenylamine-based donor with

oligothiophene or oligothienylenevinylene based-conjugated linker and dicyanovinyl,

tricyanovinyl or cyanacrylic acid groups as acceptor, was synthesized and

characterized. Their photophysical, electrochemical, thermal and luminescence

properties were studied. Transient absorption spectra of TPA-OTV-DCN in

dichloromethane solution on the pico- to nanosecond timescale were recorded after

femtosecond laser excitation at 400 nm. A transient signal at ca. 700 nm was

tentatively assigned to result from the formation of a charge-separated

[(TPA-OTV)+??DCN??] state with the charge recombination rate constant determined

to be 5.3 × 109 s?1. The energy levels of the LUMOs of TPA-OTV1-DCN,

TPA-OTV2-DCN, TPA-OTV3-DCN TPA-TAZ1-DCN, TPA-TAZ2-DCN and

TPA-o-4Th-DCN were calculated to be of ca. ?3.9 eV, establishing the formation of a

downhill driving force for the energetically favorable electron transfer process

involving the injection of an electron into the LUMO of the C60 acceptor. The

majority of the compounds were found to exhibit photovoltaic properties. The

photovoltaic responses were characterized by current-voltage measurements under

illumination of air mass (AM) 1.5G sunlight (100 mW cm–2).