Optical gating with organic building blocks : A quantitative model for the fluorescence modulation of photochromic perylene bisimide dithienylcyclopentene triads

We investigated the capability of molecular triads, consisting of two strong fluorophores that were covalently linked to a photochromic molecule, for optical gating. Therefore we monitored the fluorescence intensity of the fluorophores as a function of the isomeric state of the photoswitch. From the analysis of our data we develop a kinetic model that allows us to predict quantitatively the degree of the fluorescence modulation as a function of the mutual intensities of the lasers that are used to induce the fluorescence and the switching of the photochromic unit. We find that the achievable contrast for the modulation of the fluorescence depends mainly on the intensity ratio of the two light beams and appears to be very robust against absolute changes of these intensities. The latter result provides valuable information for the development of all-optical circuits which would require to handle different signal strengths for the input and output levels

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Storage and Processing of Information Using Molecules: The All-Photonic Approach with Simple and Multi-Photochromic Switches

The use of photochromes for the implementation of molecular logic operations is a very promising approach toward molecular computing. This statement is based on a) the possibility of operating such molecular devices exclusively with photonic signals and b) spatiotemporally and remotely controlled switching, which is characteristic for photochromes. Herein, a brief overview of the application of simple photochromes and multi-photochromic conjugates for the small-scale functional integration of complicated logic circuits is given. This complements and extends efforts to design molecular photochromic memories for data storage described by many research groups worldwide

Single-molecule probing of incommensurate biphenyl

Our data on the distribution of purely-electronic linewidths of terrylene single molecules in incommensurate biphenyl crystals are compared with the data of other groups for different low-temperature organic solid hosts and with results of numerical simulations. The first two moments of the distributions measured within a narrow temperature interval have been used to calculate a single dimensionless parameter characterizing each of the respective hosts — the variation coefficient. It appears that different amorphous hosts have similar values of this coefficient, but the value obtained for the incommensurate crystal of biphenyl is significantly different. One can conclude that the remarkable single-molecule line broadening in biphenyl at 1.8 K cannot be solely explained by the interaction with two-level systems, which is considered to cause the broadening in amorphous hosts

Deliberate Switching of Single Photochromic Triads

Photochromic molecules can be reversibly converted between two bistable conformations by light, and are considered as promising building blocks in novel macromolecular structures for sensing and imaging techniques. We have studied individual molecular triads consisting of two strong fluorophores (perylene bisimide) that are covalently linked via a photochromic unit (dithienylcyclopentene) and distinguished between deliberate switching and spontaneous blinking. It was verified that the probability for observing deliberate light-induced switching of a single triad (rather than stochastic blinking) amounts to 0.8 ± 0.1. In a few exceptional cases this probability can exceed 0.95. These numbers are sufficiently large for application in sensitive biosensing, and super-resolution imaging. This opens the possibility to develop devices that can be controlled by an external optical stimulus on a truly molecular length scale

Spontaansete ja fotoindutseeritud protsesside uurimine molekulaartahkistes kõrgselektiivse optilise lisandispektroskoopia meetoditega

Spontaansete ja fotoindutseeritud protsesside uurimine molekulaartahkistes kõrgselektiivse optilise lisandispektroskoopia meetoditega Käesolev väitekiri koondab endas bifenüüli madalatemperatuursete ühismõõduta faaside lisandispektroskoopilisi uuringuid, kus lisandimolekule on kasutatud kui optilisi sonde, mille spektraalsed omadused võivad tugevasti sõltuda lisandi lähiümbrusest. Optiliseks sondiks on kasutatud terrüleeni molekule, mille kiirgusomadused lubavad seda kromofoori kasutada väga erinevateks spektroskoopilisteks uuringuteks, sealhulgas ka ühe molekuli spektroskoopia tehnikaid kasutades. Töö esimeses osas on uuritud bifenüüli ühismõõduta struktuuri mõju lisanditsentri mittehomogeensetele fotoluminestsentsi spektritele. Teises osas on kasutatud kõrgselektiivseid spektroskoopia meetodeid: spektraalsälkamist ja ühe molekuli spektroskoopiat, eesmärgiga uurida lokaalse dünaamika mõju lisanditsentri elektronsiirde defaseerumisele. Leiti, et terrüleeni homogeensed joonelaiused temperatuuril 1.8 K ületavad tunduvalt eluealisi laiusi ning joonelaiuste jaotuse standardhälve ja keskväärtuse suhe bifenüülis on oluliselt erinev võrreldes polümeerides saadud väärtustega. Need tulemused näitavad et joonte laienemine bifenüülis ei ole kirjeldatav amorfsete süsteemide puhul kasutatud kahenivooliste süsteemide mudeliga. Töö kolmandas osas realiseeriti metoodika üksikmolekulide kiirguspiltide visualiseerimiseks toatemperatuuril ja jälgiti üksikmolekulide foto­lagunemist ning ruumilist difusiooni bifenüüli kristallis. Study of spontaneous and photoinduced processes in molecular solids using high-resolution optical spectroscopy This PhD thesis comprises experimental studies of incommensurate biphenyl using various techniques of molecular probe spectroscopy. Terrylene impurity molecules were used as optical probes with spectral behaviour depending on their local environment. In the first part inhomogeneous photoluminescence spectra of terrylene molecular impurities were studied to investigate the static interaction of the probe molecules with the incommensurate host structure. In the second part the dephasing of the electronic transition of the impurity molecules by local dynamic interactions was investigated using the hole-burning and single-molecule spectroscopy. Our studies at 1.8 K indicate that the terrylene single-molecule lines are much broader than if they would have the lifetime-limited width. The statistical distribution of single-molecule linewidths indicates that the ratio of the standard deviation to the mean value is significantly different from the values observed in glassy polymers. These results indicate inconsistency with the standard model of two-level systems elaborated for amorphous solids. An additional broadening of the single-molecule lines may be caused by interaction of the probe molecules with specific excitations of the incommensurate structure. In the last part the design and application of our experimental setup for single-molecule fluorescence imaging are described. The photostability and spatial diffusion of single terrylene molecules in biphenyl monocrystals at room temperature was investigated

Single-molecule probing of incommensurate biphenyl

Our data on the distribution of purely-electronic linewidths of terrylene single molecules in incommensurate biphenyl crystals are compared with the data of other groups for different low-temperature organic solid hosts and with results of numerical simulations. The first two moments of the distributions measured within a narrow temperature interval have been used to calculate a single dimensionless parameter characterizing each of the respective hosts — the variation coefficient. It appears that different amorphous hosts have similar values of this coefficient, but the value obtained for the incommensurate crystal of biphenyl is significantly different. One can conclude that the remarkable single-molecule line broadening in biphenyl at 1.8 K cannot be solely explained by the interaction with two-level systems, which is considered to cause the broadening in amorphous hosts.Authors are grateful to Artur Suisalu for stimulating discussions. Acknowledged is the support from Estonian Science Foundation Grants Nos. 6543, 7141, and 8167