Water-Soluble Perylene Diimides:  Solution Photophysics and Layer-by-Layer Incorporation into Polyelectrolyte Films

Abstract

Recently the synthesis of water-soluble and fluorescent perylene diimides has been reported (Müllen, K.; et al. Angew. Chem., Int. Ed. 2004, 43, 1528; Chem.-Eur. J. 2004, 10, 5297). We have characterized the photophysics of two of these compounds (anionic n-PDI, CAS Reg. No. 694438-88-5. and cationic p-PDI, CAS Reg. No. 817207-4-7) in pure water, dimethyl sulfoxide (DMSO), and aqueous NaCl. These studies, supported by molecular dynamics simulations, have led to the conclusion that these compounds form weakly interacting aggregated species in pure water. n-PDI and p-PDI have been incorporated in polyelectrolyte films of poly(styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDAC) following the layer-by-layer (LBL) methodology. The optical density and fluorescence intensity of the PDI-LBL films grew linearly with the number of layers, and the PDI was not extracted by subsequent polyelectrolyte deposition. The PDI fluorescence quantum yield was substantially diminished in these films, which we interpret as a self-quenching effect, enhanced by inter- and intralayer energy transfer. Energy-transfer studies to the incorporated cationic dye Brilliant Green (BG) has demonstrated that the BG resides in the same PSS-rich region as p-PDI and is largely excluded from the region that contains n-PDI (PDAC-rich).

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

“…Cyclometalated Ir(III)-m-chloro-bridged dimers, [Ir(C-N) 2 Cl] 2 , have proven to be useful starting materials for emissive Ir(III)-complexes since iridium-chlorine bonds are easily cleaved by Lewis basic groups such as pyridine [23] or phosphine. [24] In the present work, polyethyleneimine (PEI) was employed as ancillary ligands to yield water-soluble and positively charged Ir(C-N) 2 -PEI complexes (denoted as Ir-PEI complexes): Ir(dfppy) 2 -PEI, Ir(ppy) 2 -PEI, and Ir(piq) 2 -PEI, which emit three different basic colors (sky blue, green, and red, respectively). The abbreviations dfppy, ppy, and piq denote 4,6-difluoro (2-phenylpyridine), 2-phenylpyridine, and 1-phenylisoquinoline, respectively.…”

“…The abbreviations dfppy, ppy, and piq denote 4,6-difluoro (2-phenylpyridine), 2-phenylpyridine, and 1-phenylisoquinoline, respectively. 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.…”

“…[28] Because of the effective suppression of the excimer formation in CBZ-PAA, its host emission spectrum has a good spectroscopic overlap with the MLCT absorption band of the Ir-PEI complexes. It is also known that the triplet level of the host is higher than the triplet level of the blue phosphorescent dye [Ir(dfppy) 2 -PEI], which allows the efficient energy transfer from the host to guest molecules. [27] The suppression of such excimers in the current case with the CBZ-PAA is believed to originate from its molecular structure as well as the electrostatic repulsion between carboxylic acid groups in solution.…”

“…[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.…”

Controlled Fluorescence Resonance Energy Transfer from Multiple Fluorophores in Layer‐by‐Layer Assemblies

“…In particular, LbL assemblies have been employed as model structures to investigate fluorescence resonance energy transfer (FRET) that involves non‐radiative energy transfer from excited‐state donors to ground‐state acceptors 13, 21–27. A variety of donor/acceptor pairs of fluorescent dyes and semiconductor nanoparticles that are either multiply charged by themselves13, 21, 22 or covalently attached to polyelectrolytes23–27 have been incorporated into the layers of LbL assemblies to control the energy transfer process. Since FRET strongly depends on the donor‐to‐acceptor distance,28, 29 the emissions from the thin film can be tuned by adjusting the deposition sequence of neat polyelectrolytes and fluorophores.…”