Synthesis and characterization of a J-aggregating TDBC derivative in solution and in Langmuir–Blodgett films Hagit Aviv a,b , Yaakov R. Tischler a,b,n a Department of Chemistry, Bar-Ilan University, Israel b Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Israel article info Article history: Received 20 June 2014 Received in revised form 29 September 2014 Accepted 10 October 2014 Available online 18 October 2014 Keywords: J-aggregate Monolayer Langmuir–Blodgett Dye Absorbance Photoluminescence abstract Here we present the synthesis and optical characterization of a new amphiphilic cyanine dye, 1,1 0 - dioctadecane-3,3 0 -di(4-sulfobutyl)-5,5 0 ,6,6 0 -tetrachloro-benzimidazolocarbo-cyanine (C18S4). C18S4 is a derivative of the heavily studied J-aggregating cyanine dye TDBC that was designed specifically for creating stable amphiphilic monolayers when spread at an air–water interface. Unlike TDBC, which readily J-aggregates in water, we show that C18S4 introduced into water tends to produce micelles with monomeric spectral properties and only exhibits strong J-aggregation after an emulsification procedure and a week of dye reorganization. When deposited on a Langmuir Blodgett (LB) trough, C18S4 forms a stable monolayer with a repeatable isotherm. Layers transferred via LB deposition to a functionalized glass substrate show pronounced J-aggregation, depending on the surface transfer pressure. Layers transferred at 35 mN/m present an intense narrow absorption spectrum peaked at λ ¼589 nm with FWHM¼523 cm À1 (18 nm). The accompanying fluorescence shows a narrow spectrum with FWHM¼332 cm À1 (11.5 nm) and a Stokes shift less than 1 nm. The ability to create J-aggregates of C18S4 via LB deposition provides control over the J-aggregation process of TDBC-like molecules and can ultimately lead to tuning the J-aggregate coupling for specific experiments and applications. & 2014 Elsevier B.V. All rights reserved. 1. Introduction The arrangement of molecules within a monolayer can have a pronounced effect upon the photo-physical and photochemical behavior of the molecular assembly [1,2]. Langmuir–Blodgett (LB) deposition is an important method among different thin film preparation techniques to arrange various kinds of molecules into different forms of ordered monolayer assemblies. It is particularly suitable for assembling crystalline monolayers and monolayers of nano-scale aggregates with various functionalities [3–6]. In the LB technique, amphiphilic molecules spread at the air–water inter- face of an LB trough are compressed into a monolayer. These monolayers can consist of amorphous or crystalline domains of monomeric dye or different types of aggregate architectures, such as J-aggregates and H-aggregates [7–10]. With LB, high degrees of crystallinity and molecular orientation are achievable by control- ling the compression rate of the dye molecules and the surface pressure during the dipping phase of deposition. When amphi- philic molecules are transferred from the LB trough via LB deposition, they are oriented perpendicular to the LB film-plane, and the thickness of the LB films is an integer multiple of units of molecular length. Thus, it can be relatively straightforward to form a periodic crystalline system of LB films composed of the amphi- philic molecules [3]. J-aggregates of organic dyes are molecular arrangements of molecules whereby strong dipole–dipole coupling between mono- mers results in a new collective excitonic state possessing unique physical and spectral properties [11–15]. A salient feature of J-aggregation is a new optical transition that is red-shifted from the monomer absorption band and considerably narrower in spectral bandwidth. This new transition, referred to as a J-band, is also accompanied by a nearly resonant spectrally narrow fluorescence spectrum that has a minimal Stokes shift relative to the absorption spectrum. The collective nature of J-aggregate excitons is characterized by N c , the number of molecules that are coherently coupled together and over which the exciton coher- ently delocalizes. This coupling leads to ultra-fast super-radiant relaxation [16,17], boosted almost N c times faster than the uncoupled spontaneous emission rate, significant enhancement in spontaneous Raman scattering [18], and pronounced non- linearities in the absorption and emission characteristics of J- aggregates due to higher degrees of exciton diffusion and exciton– exciton annihilation [19,20]. J-aggregates of organic dyes continue to attract considerable interest as materials for optical storage [21,22], ultrafast optical Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2014.10.019 0022-2313/& 2014 Elsevier B.V. All rights reserved. n Corresponding author at: Department of Chemistry, Bar-Ilan University, Israel. Tel.: þ972 50 4168008. E-mail address: yrt@biu.ac.il (Y.R. Tischler). Journal of Luminescence 158 (2015) 376–383