Photochemical “Triode” Molecular Signal Transducer

Abstract

A molecular "hexad" in which five bis(phenylethynyl)anthracene (BPEA) fluorophores and a dithienylethene photochrome are organized by a central hexaphenylbenzene unit has been prepared. Singlet-singlet energy transfer among the BPEA units occurs on the 0.4 and 60 ps time scales, and when the dithienylethene is in the open form, the BPEA units fluoresce in the 515 nm region with a quantum yield near unity. When the dithienylethene is photoisomerized by UV light to the closed form, which absorbs in the 500-700 nm region, the closed isomer strongly quenches all of the excited singlet states of BPEA via energy transfer, causing the fluorescence quantum yield to drop to near zero. This photochemical behavior permits the hexad to function in a manner analogous to a triode vacuum tube or transistor. When a solution of the hexad is irradiated with steady-state light at 350 nm and with red light (>610 nm) of modulated intensity, the BPEA fluorescence excited by the 350 nm light is modulated accordingly. The fluorescence corresponds to the output of a triode tube or transistor and the modulated red light to the grid signal of the tube or gate voltage of the transistor. Frequency modulation, amplitude modulation, and phase modulation are all observed. The unusual ability to modulate intense, shorter-wavelength fluorescence with longer-wavelength light could be useful for the detection of fluorescence from probe molecules without interference from other emitters in biomolecular or nanotechnological applications.

Charge‐Transfer Interactions in Tris‐Donor–Tris‐Acceptor Hexaarylbenzene Redox Chromophores

“…Because these functional units are linked in this HAB framework through a central benzene ring, their molecular axes form an angle of 608 relative to each other. [5] Furthermore, we have used a pyrenesubstituted HAB to investigate exciton-coupling effects. The twist angle depends on the steric hindrance of the p systems.…”

Information gathering and processing with fluorescent molecules

“…This control feature is exploited in both digital and analog electronics. 24 Moore, Moore and Gust's 1, 25,26 consisting of a central hexaphenylbenzene surrounded by five bisphenylethynylanthracene fluorophores and a single dithienylethene photochrome, 27 is shown to have triodelike behaviour. As is well-known, 27 dithienylethene can be switched cleanly between open and closed forms.…”

Analog Applications of Photochemical Switches

“…Molecular hexad 1 ( Figure ) successfully mimics, on the molecular level, a transistor amplifier or triode vacuum tube 10. To understand this behaviour, it is essential to first understand the fundamental photophysical properties of the hexad.…”