Tailoring optical properties and stimulated emission in nanostructured polythiophene

Polythiophenes are the most widely utilized semiconducting polymers in organic electronics, but they are scarcely exploited in photonics due to their high photo-induced absorption caused by interchain polaron pairs, which prevents the establishment of a window of net optical gain. Here we study the photophysics of poly(3-hexylthiophene) configured with different degrees of supramolecular ordering, spin-coated thin films and templated nanowires, and find marked differences in their optical properties. Transient absorption measurements evidence a partially-polarized stimulated emission band in the nanowire samples, in contrast with the photo-induced absorption band observed in spin-coated thin films. In combination with theoretical modeling, our experimental results reveal the origin of the primary photoexcitations dominating the dynamics for different supramolecular ordering, with singlet excitons in the nanostructured samples superseding the presence of polaron pairs, which are present in the disordered films. Our approach demonstrates a viable strategy to direct optical properties through structural control, and the observation of optical gain opens the possibility to the use of polythiophene nanostructures as building blocks of organic optical amplifiers and active photonic devices

Conformable Nanowire-in-Nanofiber Hybrids for Low-Threshold Optical Gain in the Ultraviolet

The miniaturization of diagnostic devices that exploit optical detection schemes requires the design of light sources combining small size, high performance for effective excitation of chromophores, and mechanical flexibility for easy coupling to components with complex and nonplanar shapes. Here, ZnO nanowire-in-fiber hybrids with internal architectural order are introduced, exhibiting a combination of polarized stimulated emission, low propagation losses of light modes, and structural flexibility. Ultrafast transient absorption experiments on the electrospun material show optical gain which gives rise to amplified spontaneous emission with a threshold lower than the value found in films. These systems are highly flexible and can conveniently conform to curved surfaces, which makes them appealing active elements for various device platforms, such as bendable lasers, optical networks, and sensors, as well as for application in bioimaging, photo-cross-linking, and optogenetics

Unravelling the intricated photophysical behavior of 3-(pyridin-2-yl)triimidazotriazine AIE and RTP polymorphs

The development of purely organic materials showing multicolor fluorescent and phosphorescent behaviour represents a formidable challenge in view of practical applications. Herein the rich photophyisical behaviour of 3-(pyridin-2- yl)triimidazotriazine (TT-Py) organic molecule, comprising excitation-dependent fluorescence and phosphorescence under ambient conditions in both blended film and crystalline phase, is investigated by means of steady state, time resolved and ultrafast spectroscopies and interpreted on the basis of X-ray diffraction studies and DFT/TDDFT calculations. In particular, by proper excitation wavelength, dual fluorescence and dual phosphorescence of molecular origin can be observed together with low energy phosphorescences resulting from aggregate species. It is demonstrated that the multiple emission property is originated by the copresence, in the investigated system, of an extended polycyclic nitrogen-rich moiety (TT), strongly rigidified by p-p stacking interactions and short C\u2013H...N hydrogen bonds, and a fragment (Py) featuring partial conformational freedom

Coherent vibrational modes promote the ultrafast internal conversion and intersystem crossing in thiobases

Thionated nucleobases are obtained by replacing oxygen with sulphur atoms in the canonical nucleobases. They absorb light efficiently in the near-ultraviolet, populating singlet states which undergo intersystem crossing to the triplet manifold on an ultrashort time scale with a high quantum yield. Nonetheless there are still important open questions about the primary mechanisms responsible for this ultrafast transition. Here we track both the electronic and the vibrational ultrafast excited-state dynamics towards the triplet state for solvated 4-thiothymidine (4TT) and 4-thiouracil (4TU) with sub-30 fs broadband transient absorption spectroscopy in the ultraviolet. A global and target analysis allows us to simultaneously resolve the contributions of the different electronically and vibrationally excited states to the whole data set. Our experimental results, combined with state-of-the-art quantum mechanics/molecular mechanics simulations and Damped Oscillation Associated Spectra (DOAS) and target analysis, support that the relaxation to the triplet state is mediated by conical intersections promoted by vibrational coherences through the population of an intermediate singlet state. In addition, the analysis of the coherent vibrational dynamics reveals that, despite sharing the same relaxation mechanism and similar chemical structures, 4TT and 4TU exhibit rather different geometrical deformations, characterized by the conservation of planarity in 4TU and its partial rupture in 4TT

A Unified Experimental/Theoretical Description of the Ultrafast Photophysics of Single and Double Thionated Uracils

Photoinduced processes in thiouracil derivatives have lately attracted considerable attention due to their suitability for innovative biological and pharmacological applications. Here, sub-20 fs broadband transient absorption spectroscopy in the near-UV are combined with CASPT2/MM decay path calculations to unravel the excited-state decay channels of water solvated 2-thio and 2,4-dithiouracil. These molecules feature linear absorption spectra with overlapping ππ* bands, leading to parallel decay routes which we systematically track for the first time. The results reveal that different processes lead to the triplet states population, both directly from the ππ* absorbing state and via the intermediate nπ* dark state. Moreover, the 2,4-dithiouracil decay pathways is shown to be strongly correlated either to those of 2- or 4-thiouracil, depending on the sulfur atom on which the electronic transition localizes

Membrane Environment Enables Ultrafast Isomerization of Amphiphilic Azobenzene

G.M.P. and E.C. contributed equally to this work. G.M.P. acknowledges the financial support from Fondazione Cariplo, grant no. 2018-0979. The authors thank the financial support from the EU Horizon 2020 Research and Innovation Programme under Grant Agreement No. 643238 (SYNCHRONICS). The authors also thank Dr. Daniele Viola for helping with the analysis of the TA data.The non‐covalent affinity of photoresponsive molecules to biotargets represents an attractive tool for achieving effective cell photo‐stimulation. Here, an amphiphilic azobenzene that preferentially dwells within the plasma membrane is studied. In particular, its isomerization dynamics in different media is investigated. It is found that in molecular aggregates formed in water, the isomerization reaction is hindered, while radiative deactivation is favored. However, once protected by a lipid shell, the photochromic molecule reacquires its ultrafast photoisomerization capacity. This behavior is explained considering collective excited states that may form in aggregates, locking the conformational dynamics and redistributing the oscillator strength. By applying the pump probe technique in different media, an isomerization time in the order of 10 ps is identified and the deactivation in the aggregate in water is also characterized. Finally, it is demonstrated that the reversible modulation of membrane potential of HEK293 cells via illumination with visible light can be indeed related to the recovered trans→cis photoreaction in lipid membrane. These data fully account for the recently reported experiments in neurons, showing that the amphiphilic azobenzenes, once partitioned in the cell membrane, are effective light actuators for the modification of the electrical state of the membrane.Fondazione Cariplo. Grant Number: 2018‐0979EU Horizon 2020 Research and Innovation Programme. Grant Number: 64323

Superabsorption in an organic microcavity : toward a quantum battery

The rate at which matter emits or absorbs light can be modified by its environment, as markedly exemplified by the widely studied phenomenon of superradiance. The reverse process, superabsorption, is harder to demonstrate because of the challenges of probing ultrafast processes and has only been seen for small numbers of atoms. Its central idea—superextensive scaling of absorption, meaning larger systems absorb faster—is also the key idea underpinning quantum batteries. Here, we implement experimentally a paradigmatic model of a quantum battery, constructed of a microcavity enclosing a molecular dye. Ultrafast optical spectroscopy allows us to observe charging dynamics at femtosecond resolution to demonstrate superextensive charging rates and storage capacity, in agreement with our theoretical modeling. We find that decoherence plays an important role in stabilizing energy storage. Our work opens future opportunities for harnessing collective effects in light-matter coupling for nanoscale energy capture, storage, and transport technologies

Striated Muscle in Radical Prostatectomy Specimens: A Marker of Apical Dissection Quality and an Independent Predictor of Urinary Continence after Endoscopic Extraperitoneal Radical Prostatectomy.

INTRODUCTION: The study aimed to determine if the presence and amount of striated muscle on the apical sections of the cruciate sections of laparoscopic radical prostatectomy (LRP) specimens predict early and long-term urinary continence outcomes. PATIENTS AND METHODS: We conducted a retrospective review of our prospectively collected single surgeon LRP database. We identified patients based on their continence outcomes (continent (0 pads) or incontinent at 12 months), with an approximate even spread early continent and incontinent patients). An uropathologist separate from the urology team was blinded to outcome and assessed each patients' apical cruciate sections (H&E stained) for the presence, percentage and maximal diameter of muscle and extraprostatic tissue on these sections. Specifically 2 scoring systems were used: (1) semi-quantitative estimation of percentage of muscle on the apical cruciate sections (low 5%) and (2) percentage of total extraprostatic tissue on cruciate section (low 10%). Logistic regression and classification and regression tree analyses were performed to identify the predictors of urinary incontinence (UI). RESULTS: In total 80 patients were analyzed, 38 were continent and 42 were incontinent at 12 months follow-up. The percentage of extraprostatic tissue/muscle being an independent predictor of being wet at 12 months (p = 0.002) on multivariate regression along with age (p = 0.04). Using percentage of extraprostatic tissue in cruciate section (high >10%) to predict UI at 12 months, it yielded 71% sensitivity, 82% specificity, 81% PPV, 72% NPV and 76% accuracy. CONCLUSION: The use of simple additional reporting of muscle and extraprostatic tissue on the apical sections of RP specimens can help to better predict the likelihood of continence return