Triplet Energy Migration in Layer-by-Layer Deposited Ultrathin Polymer Films Bearing Tris(2,2‘-bipyridine)ruthenium(II) Moieties

Abstract

Ultrathin polymer films bearing tris(2,2‘-bipyridine)ruthenium(II) (Ru) moieties were fabricated by the layer-by-layer deposition technique. The triplet energy migration among the Ru moieties was investigated by emission spectroscopy for quenching of the phosphorescence of the Ru moiety by a ferrocene moiety in heterostructured layer-by-layer films. The absorbance of the Ru moiety in the films increased linearly as the number of bilayers increased, showing a linear growth of the thickness in a scale of nanometers. The quenching efficiency increased as the concentration of the Ru moiety increased. This increase in the efficiency showed that the triplet excitation energy migrates in the Ru layers. The diffusion of the excitation energy was analyzed quantitatively on the basis of one-dimensional diffusion in a finite thickness. A diffusion coefficient of 2 × 10-5 cm2 s-1 was observed in the layer-by-layer films made of a polycation with 18 mol % of Ru moiety. The root mean square of the migration distance was calculated to be 36 nm, which is much longer than a Perrin radius of 1.5 nm for the direct quenching of the Ru moiety by the ferrocene moiety and comparable to that in singlet energy migration. This efficient triplet energy migration shows that the layer-by-layer films serve as a light-harvesting system.

Triplet transport in thin films: fundamentals and applications

“…52,67,68 For example, triplet diffusion lengths of 18.0 AE 0.6 nm and 5.7 AE 0.5 nm have been measured for amorphous films of platinum(II) octaethylporphyrin (PtOEP) (phosphorescence QY = 0.45) and platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP) (phosphorescence QY = 0.51), respectively. 52 In this method, the strongly phosphorescent material is cast as a film and then a thin quenching layer (usually composed of fullerene or TiO 2 ) is brought into contact with it ( Fig.…”

Tunable Phosphorescent Emission through Energy Transfer within Multilayer Thin Films Based on a Carbazole‐Based Host and Ir(III)‐Complex Guest System

“…The substitution ratio of [Ir(C-N) 2 Cl] 2 to PEI was determined by 1 H NMR spectroscopy and their mole fractions were determined to be 18, 32, and 17 mol-% for Ir(dfppy) 2 -PEI, Ir(ppy) 2 -PEI, and Ir(piq) 2 -PEI, respectively. CBZ-PAA was prepared by the partial esterification between poly(acrylic acid) (PAA) and 9H-carbazole-9-ethanol (CBZ-EtOH) using the well-known N,N 0 -carbonyldiimidazole (CDI) chemistry with 1,8-diazabicyclo [5,4,0]undec-7-ene (DBU) as a catalyst. [25] Determination of the substitution ratio of carboxylic acid groups in PAA to carbazole-linked ester functional groups was quantified by 1 H NMR spectroscopy and its value was determined to be 50 mol-%.…”

“…[1] Because of the ability to control the film thickness on a nanometer scale, as well as to incorporate various functional materials within the multilayers, LbL deposition methods are well suited for the control of energy transfer efficiency within multilayers, [2][3][4][5][6][7][8][9][10][11][12][13] which has been known to be extremely sensitive to the distance between donor and acceptor chromophores. [14] Several research groups have already employed various donor and acceptor chromophores such as water-soluble dyes, [2] dye-labeled polyelectrolytes, [3,4] quantum dots, [5][6][7][8] and conjugated polymers [9,10] A new method to tune both phosphorescence emission intensity and spectroscopic colors based on the alternatively structured host/guest multilayer thin films prepared by the spinassisted LbL deposition is presented. Their emission characteristics are demonstrated with pairs of positively charged Ir-PEI complexes as guests and negatively charged CBZ-PAA as hosts.…”

“…They controlled the energy transfer efficiency by varying the distance between the donor and acceptor layer to investigate the internal structure of the multilayer films, [9][10][11] or to monitor the fluorescence signal based on the fluorescence quenching by varying the distance between the quencher and fluorophore layers. [12,13] The emission color has been controlled by changing the coating sequence and the adsorbed amount of two quantum dots with different colors. [5] Phosphors with high photoluminescent efficiency are important for efficient light emitting layers [8,[15][16][17] and also for better spectroscopic resolution in bioanalysis.…”

Surface Layer‐by‐Layer Chemical Deposition Reaction for Nanosized Thin‐Film Formation of Metal Complexes of 2‐Mercaptonicotinic Acid

“…The formation of various materials such as polymers, lipids, proteins, nanoparticles, and optically and electrically active materials through direct assembly on various substrates were reported. [8][9][10][11] LBL chemical deposition was recently used as a simple, direct, and efficient method for thin-film assembly of nanosized metal-8-hydroxyquinolate complexes. [12] The controlling factors affecting thin-film formation of the cobalt(II)-8-hydroxyquinolate complex by LBL chemical deposition were studied, explored, and optimized.…”