Fluorescent Red-Emitting BODIPY Oligofl uorene Star-Shaped Molecules as a Color Converter Material for Visible Light Communications

© 2014 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim at high effi ciency and brightness, but the long excited state lifetime of the phosphors restricts modulation frequency and hence the transmission rate. [ 2 ] The photoluminescence (PL) lifetime typical of the phosphor materials used is on the microsecond timescale, which limits the system bandwidth to a few megahertz (MHz). [ 5,6 ] There is currently a strong need for alternative materials for fast color converters, which can combine high illumination performance with short PL lifetimes. This combination of properties implies that the key fi gure of merit for color converter materials is a short natural radiative lifetime. Organic semiconductors offer many potential advantages as a novel color converter for VLC due to their visible band gaps, short radiative lifetime, and high photoluminescence quantum yield (PLQY). They have been applied as a color converter in vacuum-evaporated OLEDs [ 7 ] and we recently demonstrated the use of a yellow emitting conjugated polymer as a fast additive color converter for VLC. [ 8 ] To achieve high-quality sources for good color rendering, suitable materials with green or red PL are also needed to mix with the blue emission from the LED. In this paper, we explore the potential of star-shaped organic semiconductors based on boron dipyrromethene (BODIPY) cores as red-conversion material for LEDs in VLC applications. We selected BODIPY as the core of the molecules because it is a red emitter of known stability. [ 10 ] We investigate the infl uence of different substitution patterns of the BODIPY core with oligofl uorene arms, leading to different shapes of the molecules (Tand Y-shaped). In particular, we study the photophysical properties of these materials, measure their modulation bandwidth, and demonstrate their potential for VLC by achieving a data rate ten times higher than measured with a conventional phosphor color converter. BODIPY (4,4-difuoro4-bora-3a,4a-diaza-s-indacene)-based organic semiconductors have attracted signifi cant attention due to their electronic and optical properties with narrow absorption and emission bands, high PLQY, and good thermal stability. [ 9 ] Furthermore, they are solution-processable unlike previous red organic color converter materials. [ 7 ] They have been applied in many fi elds such as biology, [ 11 ] medicine, [ 12 ] solar energy, [ 13 ] and lasers [ 10 ] . BODIPYs can have red emission with lifetimes in the range of a few nanoseconds and can strongly absorb in the range of the GaN LEDs electroluminescence (≈450 nm) making them suitable candidates to be used in three-component additive coloration for VLC. Fluorescent Red-Emitting BODIPY Oligofl uorene Star-Shaped Molecules as a Color Converter Material for Visible Light Communications