Abstract
Organic luminescent materials have a wide range of practical applications, but the understanding of the relationship between molecular structure and luminescent behavior is lacking. Herein, we synthesized fluorinated bistolanes with an electron-donating alkoxy substituent at one terminal and an electron-withdrawing substituent at the other to realize systematic control of the electron-density distribution. Evaluation of the phase transition behavior revealed that most of the fluorinated bistolanes showed liquid-crystalline (LC) behavior, with the phase transition temperature depending on the terminal substituents. Additionally, the fluorinated luminophores displayed intense photoluminescence (PL) in solution and in their crystal phases. Remarkably, the PL color shifted dramatically depending on the dipole moment (μ||) along the long molecular axis; thus, PL tuning can be achieved through electronic modulation by precise control of the μ|| of the luminophore. Interestingly, in the LC phases under thermal conditions, the maximum PL band shifted by 0.210 eV upon phase transition from the crystal to smectic A LC phases, indicating that PL tuning can also be achieved by controlling the aggregated structure. These results offer a new molecular design for easily tunable PL materials using the molecular properties or external stimuli for promising applications, including light-emitting displays and PL sensing materials.
Highlights
Organic luminescent materials can be broadly classified into two groups: solution-state and solid-state luminophores
Methods demonstrated that the PL behavior depends on the electron-density distribution or aggregated structure
The PL behavior in solution clearly revealed that both λPL and the PL color changed dramatically depending on the μ|| value
Summary
Organic luminescent materials can be broadly classified into two groups: solution-state and solid-state luminophores. Significant efforts have been devoted to the discovery of novel luminescent materials, and as a result, various kinds of luminescent molecules have been developed [10,11]. There have been few systematic studies on the relationship between molecular structure and luminescent behavior, even though luminescence tuning is a key feature for practical light-emitting applications. We have developed a significant interest in functional materials, e.g., liquid-crystalline (LC) and photoluminescence (PL) materials, based fluorinated π-conjugated molecules such as pentafluorophenyl-containing tolane [18]2 of and. Bistolanes 1aA and 1bA (Figure 1a) exhibited blue-light PL in solution as well as in crystalline (Cr) phases [23].
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