N,N-Dimethylaniline and 1-(trifluoromethyl)benzene-functionalized tetrakis(ethynyl)pyrenes: synthesis, photophysical, electrochemical and computational studies Yeon Ok Lee a, y , Tuhin Pradhan a, y , Kwanghyun No b, * , Jong Seung Kim a, * a Department of Chemistry, Korea University, Seoul 136-701, Republic of Korea b Department of Chemistry, Sookmyung Women’s University, Seoul 140-742, Republic of Korea article info Article history: Received 16 November 2011 Received in revised form 21 December 2011 Accepted 21 December 2011 Available online 27 December 2011 Keywords: Tetrakis(phenylethynyl)pyrene Substitution pattern Radical stability DFT calculation abstract We have synthesized a series of tetrakis(ethynyl)pyrenes functionalized with N,N-dimethyaniline and 1- (trifluoromethyl)benzene as a peripheral electron-donor and electron-acceptor moiety, respectively. In solvatochromic studies, compounds with one peripheral donor and three peripheral acceptors (2), with two donors and two acceptors (3 and 4), with three donors and one acceptor (5) show enhanced charge transfer compared with tetra-donor (6) and tetra-acceptor (1) compounds. The redox peak reversibility depends on the number of peripheral donors and acceptors appended to tetrakis(ethynyl)pyrenes as well as on their substitution pattern as revealed by cyclic voltammetric studies. The photophysical and electrochemical properties of compounds 1e5 have been compared with compound (6) reported re- cently by J.-W. Oh et al. [Angew. Chem., Int. Ed. 2009, 48, 2522e2524]. The density functional theory (DFT) based calculations such as spin density distribution (SDD) of cation/anion radicals, electrostatic potential (ESP) density distribution, non-adiabatic reduction potentials (NRP) for cation radicals, and vertical detachment energy (VDE) for anion radicals supported the experimental observations. The differences in oxidation peak reversibility for different substitution pattern have been rationalized by calculated static first hyperpolarizability (b). Our observations would be helpful in designing new ECL-active materials, where ECL (electrogenerated chemiluminescence) efficiency can be improved through improving radical stability. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Pyrene is a polycyclic aromatic hydrocarbon (PAH). 1 Pyrene- based organic materials have been used for many purposes, espe- cially for molecular electronic devices such as organic light emitting diodes (OLEDs), 2 electronic skin, etc. The fluorescence properties of pyrene have made its derivatives suitable to be used as biological probes for the investigation of structural properties of proteins and peptides, 3 DNA recognition, 4 surfactant micelles and vesicles properties. 5 Both photophysical and electronic properties of pyr- enes have been exploited in optoelectronic devices such as organic photovoltaic cells (OPV), 6 organic field-effect transistors (OFETs), 7 organic lasers, solar cells, etc. More recently, authors have used the cruciform-type 8 structure of alkynylpyrene with peripheral multidonors substitution to prepare very efficient electrogenerated chemiluminescence (ECL) materials. 9a The key of these versatile applications of pyrene derivatives is based on the way of multifold tuning of structureeproperty relationships. Subtle changes in structure can greatly alter not only the physical properties like solubility and stability in ambient air, but also the optical and electronic properties such as energy gap, electron affinity and electron transfer efficiency; even stability of cation or anion pro- duced after electron donation or acceptance depends on structural changes at the molecular level. 10 The electrochemically generated cation and anion radical stabilities at the vicinity of electrode are very important criteria for showing ECL, which is a light emission from the excited-state molecules during electrochemical reac- tions. 9e11 There are very few examples 9a,10 of improving radical stability for improving ECL efficiency. Bard et al. 10a have improved the stability of oxidized fluorene compound for ECL by modifying the fluorene ring to 9,9 0 -spirobifluorene derivatives. Although pyrene derivatives are well known for their poor ECL properties because of the instability of cations produced electrochemically, we observed, in our previous work, 9a that ECL efficiencies of the pyrene derivatives increase proportionally with the number of peripheral donors, which correspond to their improved cation radical stability. There is no report of using peripheral acceptors appended to * Corresponding authors. E-mail addresses: hyun@sookmyung.ac.kr (K. No), jongskim@korea.ac.kr (J.S. Kim). y Equally contributed to this work. Contents lists available at SciVerse ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2011.12.066 Tetrahedron 68 (2012) 1704e1711