Photonic modulation of electron transfer with switchable phase inversion.

Photochromes may be reversibly photoisomerized between two metastable states and their properties can influence, and be influenced by, other chromophores in the same molecule through energy or electron transfer. In the photochemically active molecular tetrad described here, a porphyrin has been covalently linked to a fullerene electron acceptor, a quinoline-derived dihydroindolizine photochrome, and a dithienylethene photochrome. The porphyrin first excited singlet state undergoes photoinduced electron transfer to the fullerene to generate a charge-separated state.

A systematic method for the targeted discovery of chemical attribution signatures: application to isopropyl bicyclophosphate production.

Potential attribution signatures for the synthesis of a highly toxic bicyclophosphate, 4-isopropyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane 1-oxide (Isopropyl Bicyclophosphate or IPBCP) were discovered using a trilateral synthetic, analytical, and statistical approach.

All-photonic multifunctional molecular logic device.

Photochromes are photoswitchable, bistable chromophores which, like transistors, can implement binary logic operations. When several photochromes are combined in one molecule, interactions between them such as energy and electron transfer allow design of simple Boolean logic gates and more complex logic devices with all-photonic inputs and outputs. Selective isomerization of individual photochromes can be achieved using light of different wavelengths, and logic outputs can employ absorption and emission properties at different wavelengths, thus allowing a single molecular species to perform several different functions, even simultaneously.

An all-photonic molecular keypad lock.

Off and on: A molecular triad, consisting of a porphyrin linked to two different, independently addressable photochromic moieties, functions as a molecular keypad lock with all-photonic inputs and output. The porphyrin correlates the responses of the two inputs to light of different wavelengths and provides an appropriate output as fluorescence, which results only when one of eight possible input combinations has been applied (see figure).

Molecular all-photonic encoder-decoder.

In data processing, an encoder can compress digital information for transmission or storage, whereas a decoder recovers the information in its original form. We report a molecular triad consisting of a dithienylethene covalently linked to two fulgimide photochromes that performs as an all-photonic single-bit 4-to-2 encoder and 2-to-4 decoder. The encoder compresses the information contained in the four inputs into two outputs.

Self-regulation of photoinduced electron transfer by a molecular nonlinear transducer.

Organisms must adapt to survive, necessitating regulation of molecular and subcellular processes. Green plant photosynthesis responds to potentially damaging light levels by downregulating the fraction of excitation energy that drives electron transfer. Achieving adaptive, self-regulating behaviour in synthetic molecules is a critical challenge that must be met if the promises of nanotechnology are to be realized.

All-photonic molecular half-adder.

One molecule acts as both an AND and an XOR Boolean logic gate that share the same two photonic inputs. The molecule comprises a half-adder, adding two binary digits with only light as inputs and outputs, and consists of three covalently linked photochromic moieties, a spiropyran and two quinoline-derived dihydroindolizines. The AND function is based on the absorption properties of the molecule, whereas the XOR function is based on an off-on-off response of the fluorescence to the inputs that results from interchromophore excited-state quenching interactions.

Molecular AND and INHIBIT gates based on control of porphyrin fluorescence by photochromes.

A molecular triad consisting of a porphyrin (P) covalently linked to two photochromes-one from the dihydroindolizine family (DHI) and one from the dihydropyrene family (DHP)-has been synthesized and found to act as either a molecular AND logic gate or an INHIBIT gate, depending on the inputs and initial state of the photochromes. The basis of these functions is quenching of porphyrin fluorescence (output of the gates) by the photochromes. The spiro form of DHI does not quench porphyrin fluorescence, whereas its betaine isomer strongly quenches by photoinduced electron transfer.

Photochromic control of photoinduced electron transfer. Molecular double-throw switch.

A molecular double-throw switch that employs a photochromic moiety to direct photoinduced electron transfer from an excited state donor down either of two pathways has been prepared. The molecular triad consists of a free base porphyrin (P) linked to both a C(60) electron acceptor and a dihydroindolizine (DHI) photochrome. Excitation of the porphyrin moiety of DHI-P-C(60) results in photoinduced electron transfer with a time constant of 2.