Photoinduced intramolecular reactions in triphenylamine–corrole dyads Lingamallu Giribabu *, Kolanu Sudhakar Inorganic & Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad, 500007 (Telangana), India A R T I C L E I N F O Article history: Received 10 July 2014 Received in revised form 26 August 2014 Accepted 16 September 2014 Available online 22 September 2014 Keywords: Corrole Triphenylamine Intramolecular Energy transfer Electron transfer Time-resolved A B S T R A C T Donor–Acceptor systems, in which a donor triphenylamine (TPA) directly connected to a corrole (Cor) acceptor (TPA-Cor) and separated by an ethynylphenyl bridge between TPA and Cor (TPA-E-Cor) have been designed, synthesized and fully characterized by elemental analysis, MALDI-MS, UV–Visible and 1 H NMR spectroscopic methods. A comparison of the UV–Visible and 1 H NMR features of these D–A systems with those of the corresponding individual model compounds (i.e., TPA and Cor) reveal that there exist minimum p–p interactions between triphenylamine and corrole p-planes. Quenched emission of triphenylamine (but not corrole) part of both the dyads have been observed in three different solvents. Excitation spectral data provides evidence for an intramolecular excitation energy transfer (EET) from the singlet triphenylamine to the corrole. Detailed analysis of the data suggests that Forster’s dipole–dipole mechanism does not adequately explain this energy transfer but, an electron exchange mediated mechanism can, in principle, contribute to the intramolecular EET. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction The conversion of solar light into valuable energy by natural or artificial photosynthesis is an appealing and intriguing process, making it an interesting topic for researchers in biology, physics and chemistry [1–4]. In natural photosynthesis, the initial charge separation reaction in the heart of the reaction center, the photogenerated positive and negative charges are moved apart to suppress the recombination reaction. The energy of the resulting long-lived charges is subsequently used to drive biochemical processes [5,6]. Photosynthesis represents a noteworthy and ubiquitous model that has motivated design of many elaborate assemblies to convert light energy into chemical potential. A great variety of donor–acceptor (D–A) systems have been reported in the literature in order to understand initial events of photosynthetic process [7–9]. Porphyrins almost monopolize the study of photoactive arrays, due to their easy availability and large body of information on their synthetic manipulations, electrochemical and photophysical pro- cesses [10–15]. In contrast, investigation of corroles, contracted porphyrin analogs lacking one meso-carbon atom has been over- shadowed by porphyrin science, partly due to the challenging corrole synthesis. Recent increased interest in corrole-based materials and their applications is in great part due to the impressive synthetic progress that has been made in the field over the last one and half decade, as catalysts for organic transformation, sensors and as sensitizers for photodynamic therapy as well as dye-sensitized solar cells applications [16–22]. We are particularly interested in the design of corrole based D–A systems. A few corrole based D–A systems have been reported in order to understand the initial events of natural photosynthesis [23–29]. For example, Nao et al. have constructed mixed corrole–porphyrin multi chromophoric systems and studied singlet–singlet energy transfer process by using transient absorption spectroscopy [25]. D’souza and co-workers have reported corrole–fullerene D–A system and studied the excited state dynamics [28]. It was found that the rate of charge separated state 10 10  10 11 s 1 . Recently, Brizet et al. have explained the modulation of singlet energy transfer in gallium corrole-BODIPY dyad systems in which the direction of energy transfer depends upon the type of substituents present on BODIPY [23] . As part of our continuing interest in studying the photoinduced processes of corrole based D–A systems, hereby, we report design, synthesis, spectral (UV–Visible, ESI-MS and 1 H NMR) and electrochemical characterization of molecular dyads in which a donor triphenylamine has directly connected to a corrole (TPA-Cor) and an ethynylphenyl spacer in between (TPA-E-Cor). In addition, more emphasis focused on photophysical properties of a novel triphenylamine and corrole dyads (Scheme 1). * Corresponding author. Tel.: +91 40 27191724; fax: +91 40 27160921. E-mail address: giribabu@iict.res.in (L. Giribabu). http://dx.doi.org/10.1016/j.jphotochem.2014.09.008 1010-6030/ ã 2014 Elsevier B.V. All rights reserved. Journal of Photochemistry and Photobiology A: Chemistry 296 (2014) 11–18 Contents lists available at ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journal homepa ge: www.elsev ier.com/locate/jphotochem