Sensors and Actuators B 150 (2010) 655–666 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Novel PAMAM light-harvesting antennae based on 1,8-naphthalimide: Synthesis, energy transfer, photophysical and pH sensing properties Nikolai I. Georgiev, Vladimir B. Bojinov ∗ , Nevena Marinova Department of Organic Synthesis, University of Chemical Technology and Metallurgy, 8 Kliment Ohridsky Str., 1756 Sofia, Bulgaria article info Article history: Received 11 October 2009 Received in revised form 9 July 2010 Accepted 18 August 2010 Available online 26 August 2010 Keywords: 1,8-Naphthalimide Polyamidoamine (PAMAM) Fluorescence Light-harvesting antennae Energy transfer pH sensing Photoinduced electron transfer (PET) abstract This work presents the design, convergent synthesis and spectral characteristics of novel PAMAM den- drons, core and peripherally functionalized with 1,8-naphthalimide fluorophores. The novel compounds were configured as light-harvesting antennae where the system surface is labeled with a different num- ber of blue-emitting 4-allyloxy-1,8-naphthalimide “donor” fluorophores capable of absorbing light and efficiently transferring the energy to a single yellow-green emitting 4-alkylamino-1,8-naphthalimide “acceptor” dye. The overlap between the blue emission of the donor periphery and the absorption of the acceptor (focal dye) was more than 95%. Novel light-harvesting systems showed highly efficient energy transfer (91–94%). Nevertheless fluorescence quenching of the core chromophore was observed, which is related to a possible photoinduced electron transfer (PET) from the 4-alkoxy-1,8-naphthalimide periph- ery towards the focal 4-alkylamino-1,8-naphthalimide. Novel PAMAM light-harvesting systems were also configured in a “fluorophore–spacer–receptor” format, and as such, displayed sensitive fluorescence signaling over a wide pH scale, which is attributed to a PET process from the tertiary amines in the den- dron bone to the fluorophores. This assigns the synthesized light-harvesting antennae to potential use as highly efficient pH chemosensing materials. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Because of their strong fluorescence and good photostability, the 1,8-naphthalimide derivatives have found application in a number of areas. They have been used as fluorescent dyes for polymer mate- rials [1,2], laser active media [3,4], fluorescent markers in biology [5], anticancer agents [6] and analgesics [7] in medicine, fluores- cence switchers and sensors [8,9], light emitting diodes [10,11], electroluminescent materials [12,13], liquid crystal displays [14,15] and ion probes [16]. Considering the need for effectively using renewable energy sources, molecular systems capable of light-harvesting and energy transfer are currently of great interest [17,18]. Nature has already evolved an effective pathway for harvesting sunlight into useful chemical energy. The remarkable character of the photosynthetic system is that the energy of any photon absorbed by antenna com- plexes is transferred with greater than 90% efficiency. Progress in the study of natural photosynthetic systems has provided the impetus to design artificial light-harvesting assemblies based on a variety of architectures [19–31]. Dendritic light-harvesting assem- blies have also attracted much attention because of their structures, ∗ Corresponding author. Tel.: +359 2 8163206. E-mail address: vlbojin@uctm.edu (V.B. Bojinov). reminiscent of the architecture of natural light-harvesting com- plexes [32–41]. Non-conjugated poly(benzyl ether) dendron-based light- harvesting systems have been explored intensely; however, up to now, reports about flexible aliphatic-scaffold light-harvesting dendritic systems, such as polyamidoamine (PAMAM) dendron- based light-harvesting systems, are still very scarce [42–46]. It is well known that poly(amidoamine)s form a novel class of indus- trial dendrimers which possess a definite molecular composition with different functional groups. Our first investigations on the synthesis and photophysical properties of some new PAMAM light-harvesting antennae, core and periphery functionalized with three 1,8-naphthalimide units (one acceptor and two donors), were published previously [44,45]. Studying their fluorescence properties at different pH values a photoinduced electron transfer (PET) from PAMAM backbone to the 1,8-naphthalimide fluo- rophores has been observed, making them of potential use as chemosensing materials. The basic goal in the design of light-harvesting antennae is assembling a number of donor units around a single accep- tor core. Increasing the number of donor fluorophores leads to higher extinction coefficient of the systems that improves their ability to harvesting photons. In this paper, we report on the design, synthesis and photophysical properties of fluorescence light-harvesting antennae based on core and peripherally 1,8- 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.08.023