N,N-Dimethylaniline and 1-(trifluoromethyl)benzene-functionalized tetrakis(ethynyl)pyrenes: Synthesis, photophysical, electrochemical and computational studies

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 1-5 have been compared with compound (6) reported recently by J.-W. Oh et al. [Angew. Chem., Int. Ed. 2009, 48, 2522-2524]. 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 (β). Our observations would be helpful in designing new ECL-active materials, where ECL (electrogenerated chemiluminescence) efficiency can be improved through improving radical stability.