The excitonic circuitry found in photosynthetic organisms suggests an alternative to electronic circuits, but the assembly of optically active molecules to fabricate even simple excitonic devices has been hampered by the limited availability of suitable molecular scale assembly technologies. Here we have designed and operated a hybrid all-optical excitonic switch comprised of donor/acceptor chromophores and photochromic nucleotide modulators assembled with nanometer scale precision using DNA nanotechnology. The all-optical excitonic switch was operated successfully in both liquid and solid phases, exhibiting high ON/OFF switching contrast with no apparent cyclic fatigue through nearly 200 cycles. These findings, combined with the switch’s small footprint and volume, estimated low energy requirement, and potential ability to switch at speeds in the 10s of picoseconds, establish a prospective pathway forward for all-optical excitonic circuits.

Nucleosidic and oligonucleotidic diarylethenes (DAEs) are an emerging class of photochromes with high application potential. However, their further development is hampered by the poor understanding of how the chemical structure modulates the photochromic properties. Here we synthesized 26 systematically varied deoxyuridine-and deoxycytidine-derived DAEs and analyzed reaction quantum yields, composition of the photostationary states, thermal and photochemical stability, and reversibility. This analysis identified two high-performance photoswitches with near-quantitative, fully reversible back-and-forth switching and no detectable thermal or photochemical deterioration. When incorporated into an oligonucleotide with the sequence of a promotor, the nucleotides maintained their photochromism and allowed the modulation of the transcription activity of T7 RNA polymerase with an up to 2.4-fold turnoff factor, demonstrating the potential for optochemical control of biological processes.

Photoswitches based on the diarylethene architecture have been attracting considerable attention for the investigation and control of a variety of biological processes. The reversible photoisomerization reaction between their open- and closed-ring forms can be selectively addressed by irradiation with light of two markedly different wavelengths. In this work, the dynamics of the photochromic ring-opening reaction of four novel diarylethene-based photoswitchable deoxyuridine nucleosides is investigated by femtosecond transient absorption. Upon photoexcitation with sub-20 fs pulses in the first absorption band (500 nm), all four photoswitches showed a fast ballistic excited-state deactivation within less than 500 fs toward the S1/S0 conical intersection. Transient data was globally analyzed, and a relaxation kinetic model with a branching between open and closed ring forms without any loss channels was derived. Ring-opening quantum yields, Φr-o, were found to strongly depend on the substituents (R), ranging from 0.64 (dU(PSI): R = 2-naphthyl) to 0.30 (dU(PSIV): R = 2-pyridyl).

SummaryDiarylethenes are an important class of reversible photoswitches and often claimed to require two alkyl substituents at the carbon atoms between which the bond is formed or broken in the electrocyclic rearrangement. Here we probe this claim by the synthesis and characterization of four pairs of deazaadenine-based diarylethene photoswitches with either one or two methyl groups at these positions. Depending on the substitution pattern, diarylethenes with one alkyl group can exhibit significant photochromism, but they generally show poor stability towards extended UV irradiation, low thermal stability, and decreased fatigue resistance. The results obtained provide an important direction for the design of new efficient DNA photoswitches for the application in bionanotechnology and synthetic biology.

Nucleosidic and oligonucleotidic diarylethenes (DAEs) are an emerging class of photochromes with high application potential. However,t heir further development is hampered by the poor understanding of how the chemical structure modulates the photochromic properties.H ere we synthesized 26 systematically varied deoxyuridine-and deoxycytidine-derived DAEs and analyzed reaction quantum yields, composition of the photostationary states,t hermal and photochemical stability,and reversibility.This analysis identified two high-performance photoswitches with near-quantitative,f ully reversible back-and-forth switching and no detectable thermal or photochemical deterioration. When incorporated into an oligonucleotide with the sequence of ap romotor,t he nucleotides maintained their photochromism and allowed the modulation of the transcription activity of T7 RNAp olymerase with an up to 2.4-fold turn-off factor,d emonstrating the potential for optochemical control of biological processes.