Block modification of rod-shaped π conjugated carbon frameworks with donor and acceptor groups toward highly fluorescent molecules: synthesis and emission characteristics

Abstract

To create organic molecules that are highly fluorescent at a longer wavelength region, we investigated the synthesis (using Pd-catalyzed cross-coupling) and photophysical properties (Φ_f, λ_em, τ, λ_abs, and ε) of the following π conjugated molecular rods consisting of p-phenyleneethynylene units modified by donor (OMe) and/or acceptor (CN) groups: (1) side-donor modification systems (SD systems), (2) side-acceptor modification systems (SA systems), and (3) systems consisting of a donor block and an acceptor block (BL systems). As a consequence, very high Φ_f values (>0.95) were obtained for BL systems. Bathochromic shifts of λ_em for the same π conjugation length were largest for BL systems. Thus we succeeded in creating highly efficient light emitters at a longer wavelength region by block modification (e.g., Φ_f = 0.97, λ_em = 464 nm for BL-9). Considerably intense solid emission (Φ_f ∼ 0.5) at a longer wavelength region (500–560 nm) was also found for BL systems. It has been found that BL-6 and BL-8 exhibit interesting two photon absorption characteristics.