Full-Color Fluorescence Solvatochromism of Push-Pull Type Indenoindene Derivatives

Full-color fluorescence solvatochromism was demonstrated using two carbon-bridged oligo(phenylenevinylene) (COPV) derivatives Ph2N-COPV1(Bu)-COCH3 and [Ph2N-COPV1(Bu)]2CO with a push-pull system, where the donor and acceptor moieties are diphenylamino and a carbonyl group, respectively. In non-polar cyclohexane, the molecules exhibited blue photoluminescence (lambda PL=443 and 464 nm) with a locally excited character, while in polar solvents, a charge-transfer character emerged. In methanol, red emission was observed (lambda PL=602 and 572 nm). The difference in luminescence maxima between cyclohexane and methanol corresponds to 0.74 and 0.59 eV for Ph2N-COPV1(Bu)-COCH3 and [Ph2N-COPV1(Bu)]2CO, respectively, which are larger than those of previously reported push-pull systems. The photoluminescence quantum yields of Ph2N-COPV1(Bu)-COCH3 in aprotic solvents were 0.90 and higher regardless of solvent polarity, while they decreased in protic solvents. The molecules also display high extinction coefficients of up to 2.8x104 and 6.4x104 M-1 cm-1. These data demonstrate the effectiveness of the use of structurally rigid planar COPV framework. Furthermore, [Ph2N-COPV1(Bu)]2CO showed significant responses to water content in tetrahydrofuran-water mixed solvents, which highlights its potential for sensing applications.