Supramolecular assembly of dipeptide functionalized benzo[ghi]perylene monoimide directs white light emission via donor–acceptor interactions

Abstract

An aromatic dipeptide Phe-Phe (FF) functionalized benzo[ghi]perylene monoimide (BPI) is synthesized and its optical behaviour and self-assembly nature in different organic solvents are studied. Diels–Alder reaction of perylene and N,N′-maleoyl-Phe-Phe-OMe produces a new fluorophores (BPI-FF-OMe) which is highly soluble in a wide range of organic solvents without any swallow alkyl chain. The dipeptide appended benzo[ghi]perylene monoimide (BPI-FF-OMe) self-assembles into nanospheres both in methanol and toluene solvents. The nanospherical structures are driven by hydrogen bonding and π–π stacking interactions among aromatic dipeptide appended benzo[ghi]perylene monoimide. The self-assembled nano-architecture of BPI-FF-OMe is studied by a number of microscopic techniques. Tunable solvent dependent photophysical behavior of BPI-FF-OMe is also studied. The synthesized BPI-FF-OMe exhibits positive solvatochromic emission (λ_em (toluene) = 508 nm; λ_em (methanol) = 566 nm) as a function of solvent polarity with higher lifetimes (τ_toluene = 8.4 ns; τ_methanol = 5.7 ns) and quantum yields (ϕ_f = 0.55 (toluene); ϕ_f = 0.39 (methanol)). The BPI-FF-OMe shows white light emission upon energy transfer between donor pyrenebutyric acid (PyBA) to acceptor BPI-FF-OMe molecule. In order to study the role of peptide sequence Phe-Phe attached with perylene moiety of BPI-FF-OMe molecule, an amino acid leucine (L) functionalized BPI-L-OMe molecule is also synthesized. BPI-L-OMe also shows white light emission upon energy transfer from donor pyrenebutyric acid (PyBA) molecules to acceptor BPI-L-OMe molecules. Benzo[ghi]perylene moiety plays an important role for energy transfer from donor pyrene moiety to acceptor benzo[ghi]perylene moiety that exhibits white light emission.