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We report the synthesis of a dibenzodinaphthocoronene (DBDNC) derivative as a novel nanographene with armchair, zigzag, and fjord edges, which was characterized by NMR and X-ray crystallography as well as infrared (IR) and Raman spectroscopies. Ultrafast transient absorption (TA) spectroscopy revealed the presence of stimulated emission signals at 655 nm and 710 nm with a relatively long lifetime, which resulted in dual amplified spontaneous emission (ASE) bands under ns-pulsed excitation, indicating the promise of DBNDC as a near-infrared (NIR) fluorophore for photonics. Our results provide new insight into the design of nanographene with intriguing optical properties by incorporating fjord edges.

Los compuestos orgánicos conjugados han sido investigados ampliamente debido a su versatilidad para integrarse con otros materiales a través de métodos de bajo coste y a su idoneidad para una amplia gama de aplicaciones optoelectrónicas; por ejemplo, transistores de efecto de campo, células solares, LEDs y láseres, entre otros. Actualmente existe un interés particular en los materiales orgánicos para láser promovido por el desarrollo de aplicaciones biomédicas y de telecomunicaciones. De hecho, el desarrollo de técnicas bottom-up en la síntesis orgánica y de métodos computacionales químico-cuánticos permiten el diseño inteligente de compuestos orgánicos con propiedades a medida que pueden ser beneficiosas para tales aplicaciones. En este sentido, comprender la relación entre las características estructurales de los compuestos orgánicos y sus propiedades optoelectrónicas es una etapa obligatoria en el proceso de diseño. En el desarrollo de esta tesis se evalúan las propiedades fotofísicas de dos familias de compuestos orgánicos –perilenodiimidas y nanografenos– dispersos en matrices inertes con el objetivo de mejorar su funcionamiento como materiales activos para láseres. En particular, se han llevado a cabo tres actuaciones: 1) la investigación sistemática de dos polímeros termoplásticos comerciales, poliestireno y polimetilmetacrilato, como matrices inertes para dispersar compuestos de perilenodiimida con un enfoque en optimizar las propiedades de la guía de ondas y reducir los requisitos de energéticos de los dispositivos; 2) conocer los mecanismos de fotodegradación y quenching de la fotoluminiscencia en derivados de perilenodiimida dispersos en películas de poliestireno con el objetivo de obtener dispositivos más duraderos y eficientes; y 3) estudiar las propiedades fotofísicas de compuestos novedosos de la familia de los nanografenos dispersos en matrices inertes con el fin de comprender la relación entre su estructura –borde, heteroátomos, sustituyentes– y su

The molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD) has been widely used in optoelectronic applications, mainly for its hole-transporting properties, but also for its capability to emit blue light and amplified spontaneous emission, which is important for the development of organic lasers. Here, we report deep-blue-emitting distributed feedback (DFB) lasers based on TPD dispersed in polystyrene (PS), as active media, and dichromated gelatin layers with holographically engraved relief gratings, as laser resonators. The effect of the device architecture (with the resonator located below or on top of the active layer) is investigated with a dye (TPD) that can be doped into PS at higher rates (up to 60 wt%), than with previously used dyes (<5 wt%). This has enabled changing the index contrast between film and resonator, which has an important effect on the laser performance. With regards to thresholds, both architectures behave similarly for TPD concentrations above 20 wt%, while for lower concentrations, top-layer resonator devices show lower values (around half). Remarkably, the operational durability of top-layer resonator devices is larger (in a factor of around 2), independently of the TPD concentration. This is a consequence of the protection offered by the resonator against dye photo-oxidation when the device is illuminated with pulsed UV light.

The spectral overlap between stimulated emission (SE) and absorption from dark states (i.e. charges and triplets) especially in the near-infrared (NIR), represents one of the most effective gain loss channel in organic semiconductors. Recently, bottom-up synthesis of atomically precise graphene nanostructures, or nanographenes (NGs), has opened a new route for the development of environmentally and chemically stable materials with optical gain properties. However, also in this case, the interplay between gain and absorption losses has hindered the attainment of efficient lasing action in the NIR. Here, we demonstrate that the introduction of two fluoranthene imide groups to the NG core leads to a more red-shifted emission than the precursor NG molecule (685 vs. 615 nm) and also with a larger Stokes (45 nm vs. 2 nm, 1026 cm-1 vs. 53 cm-1, respectively). Photophysical results indicate that, besides the minimisation of ground state absorption losses, such substitution permits to suppress the detrimental excited state absorption in the NIR, which likely arises from a dark state with charge-transfer character. This has enabled NIR lasing (720 nm) from all-solution processed distributed feedback devices with one order of magnitude lower thresholds than those of previously reported NIR-emitting NGs. This study represents an advance in the field of NGs and, in general, organic semiconductors photonics, towards the development of cheap and stable NIR lasers.

Perylenediimide (PDI) compounds with no substituents in their core are widely used as the active units of thin-film organic lasers. Recently, bay-substituted PDIs (b-PDIs) bearing two sterically hindering diphenylphenoxy groups at the 1,7-bay positions have received great attention because they show red-shifted emission with respect to bay-unsubstituted PDIs, while maintaining high photoluminescence (PL) quantum yields and low amplified spontaneous emission (ASE) thresholds even at high doping rates. However, their ASE photostability is relatively low compared to that of state-of-the-art PDIs. Thus, the design of b-PDIs with improved ASE photostability remains a challenge. Here, the synthesis of two b-PDIs with phenyl-type substituents at the imide positions is reported. Complete characterization of their optical properties, including absorption, PL, ASE, and transient spectroscopy, supported also by quantum chemical calculations, is performed with the dyes diluted in either a liquid solvent or a polystyrene film. Film experiments were accomplished at very low doping rates, to resemble the isolated molecule behavior, and also in a range of increasing doping rates, to investigate concentration quenching effects. The reported b-PDIs show improved ASE photostability (3-fold) with respect to b-PDIs with aliphatic-type substituents at the imide positions, whilst they show more propensity toward aggregation.

High-transparency polymers, called optical polymers (OPs), are used in many thin-film devices, for which the knowledge of film thickness (h) and refractive index (n) is generally required. Spectrophotometry is a cost-effective, simple and fast non-destructive method often used to determine these parameters simultaneously, but its application is limited to films where h > 500 nm. Here, a simple spectrophotometric method is reported to obtain simultaneously the n and h of a sub-micron OP film (down to values of a few tenths of a nm) from its transmission spectrum. The method is valid for any OP where the n dispersion curve follows a two-coefficient Cauchy function and complies with a certain equation involving n at two different wavelengths. Remarkably, such an equation is determined through the analysis of n data for a wide set of commercial OPs, and its general validity is demonstrated. Films of various OPs (pristine or doped with fluorescent compounds), typically used in applications such as thin-film organic lasers, are prepared, and n and h are simultaneously determined with the proposed procedure. The success of the method is confirmed with variable-angle spectroscopic ellipsometry.

Chemically synthesized zigzag-edged nanographenes (NG) have recently demonstrated great success as the active laser units in solution-processed organic distributed feedback (DFB) lasers. Here, we report the first observation of dual amplified spontaneous emission (ASE) from a large-size NG derivative (with 12 benzenoid rings) dispersed in a polystyrene film. ASE is observed simultaneously at the 685 and 739 nm wavelengths, which correspond to different transitions of the photoluminescence spectrum. Ultrafast pump-probe spectroscopy has been used to ascertain the underlying photophysical processes taking place in the films. DFB lasers, based on these materials and top-layer nanostructured polymeric resonators (i.e., one or two-dimensional surface relief gratings), have been fabricated and characterized. Lasers emitting close to either one of the two possible ASE wavelengths, or simultaneously at both of them, have been prepared by proper selection of the resonator parameters.

The efficient synthesis and electronic properties of two large‐size cove‐edged nanographenes (NGs), CN1 and CN2, are presented. X‐ray crystallographic analysis reveals a contorted backbone for both molecules owing to the steric repulsion at the inner cove position. Noticeably, the dominant structures of these molecules contain four (for CN1) or six (for CN2) localized C=C double bonds embedded in nine (for CN1) or twelve (for CN2) aromatic sextet rings according to Clar's formula, which is supported by bond length analysis and theoretical (NICS, ACID) calculations. Furthermore, Raman spectra exhibit a band associated with the longitudinal CC stretching mode of olefinic double bonds. Owing to the existence of the additional olefinic bonds, both compounds show a small band gap (1.84 eV for CN1 and 1.37 eV for CN2). They also display moderate fluorescence quantum yield (35 % for CN1 and 50 % for CN2) owing to the contorted geometry, which can suppress aggregation in solution.

The design and fabrication of thin-film based organic optoelectronic devices require knowledge of the film optical properties. A low-cost and non-destructive method often used for optical characterization of films is the well-established spectrophotometric envelope method. However, this method is typically limited to thickness above 400 nm, a value often higher than that of the films involved in these devices. This paper studies a procedure to obtain the thickness of sub-400 nm active films from their spectrophotometric trace when the refractive index is previously known. The proposed procedure is based on comparing the experimental transmission spectrum in the transparent spectral window with that obtained by simulation. The capabilities of the proposed method are demonstrated here by its application in the fabrication of organic distributed feedback lasers, for which a fine control of film thickness is important to obtain an optimized and reproducible response. Results are verified with other techniques, such as ellipsometry and profilometry. Thus, with the proposed method, film thickness can be easily determined down to 40 nm maintaining an accuracy of about 5 nm even for films with low refractive index (1.5–1.7). Different methods to determine refractive index of these films are also discussed.

The chemical synthesis of nanographene molecules constitutes the bottom-up approach toward graphene, simultaneously providing rational chemical design, structure-property control and exploitation of their semiconducting and luminescence properties. Here, we report nanographene-based lasers from three zigzag-edged polycyclic aromatics. The devices consist of a passive polymer film hosting the nanographenes and a top-layer polymeric distributed feedback resonator. Both the active material and the laser resonator are processed from solution, key for the purpose of obtaining low-cost devices with mechanical flexibility. The prepared lasers show narrow linewidth ( < 0.13 nm) emission at different spectral regions covering a large segment of the visible spectrum, and up to the vicinity of the near-infrared. They show outstandingly long operational lifetimes (above 105 pump pulses) and very low thresholds. These results represent a significant step forward in the field of graphene and broaden its versatility in low-cost devices implying light emission, such as lasers.

Perylenediimide (PDI) dyes dispersed in polymer films have demonstrated great success as active materials in thin-film organic lasers (TFOLs). The type of matrix used to host the dye and the dye doping rate are both crucial parameters to optimize laser performance. This work reports the study of two soluble PDIs, the comercial derivative perylene orange (PDI-O) emitting at around 580 nm, and a new dye (b-PDI-A) with substituents at the 1,7 bay positions of the PDI core emitting at around 620 nm, dispersed at different doping levels (up to 8 and 50 wt %, for PDI-O and b-PDI-A, respectively) in two widely used polymers for optoelectronics, polystyrene (PS) and poly(methyl methacrylate) (PMMA). The main goal is to determine which of these two polymers, and at which dye concentration, provides the best results for their use in TFOLs. The assessment of the active materials has been carried out through the analysis of their absorption, photoluminescence, and amplified spontaneous emission (ASE) properties. Their capability to form high-quality optical waveguides has also been studied by determining gain coefficients and waveguide losses. Results have shown that for both types of PDI derivatives PS is better than PMMA at any concentration, which means larger photoluminescence efficiency, lower ASE thresholds, longer ASE operational lifetimes, larger gain, and lower propagation waveguide losses. In addition, the onset concentration at which dye aggregation becomes significant as to negatively affect the optical properties is lower in PMMA than in PS; thus, the larger the blending ratio, the larger the superiority of PS with respect to PMMA is.

L’aprenentatge dels conceptes físics per part de l’alumnat es pot assolir d’una manera més significativa si les classes teòriques s’acompanyen d’experiències que permeten il·lustrar-lo de forma pràctica. En aquest treball, s’hi proposa un experiment per a mesurar la velocitat del so en l’aire, on s’utilitza el concepte d’ones estacionàries en un tub semitancat. Consisteix en la generació i l’emissió d’ones sonores d’una determinada freqüència a la part oberta del tub, mitjançant un telèfon mòbil, i mesurar la intensitat del so de l’ona sonora reflectida amb un altre telèfon mòbil. El senyal acústic, en rebotar al fons del tub, produeix una ona estacionària només per a determinades llargàries del tub. En aquesta situació hi ha una relació entre la freqüència de ressonància de l’ona sonora incident, la longitud del tub i la velocitat de propagació del so en l’aire. I si determinem experimentalment la longitud del tub i la freqüència de ressonància és possible obtenir la velocitat del so en l’aire.

La realització d’experiments de física utilitzant noves tecnologies és sovint més atractiva per als estudiants que els experiments convencionals. En aquest treball usem la targeta de so d’un ordinador per a mesurar el temps que transcorre entre dos sons. Hem portat a terme dos experiments per a calcular l’acceleració de la gravetat, on hem utilitzat la targeta de so de l’ordinador i el programa Audacity de gravació i edició de sons. El primer experiment es basa en la cinemàtica del tir parabòlic d’un cos, mentre que el segon experiment està basat en la llei d’inducció de Faraday quan un imant cau per un tub no metàl·lic on hi ha espires enrotllades. D’aquesta manera, hem obtingut l’acceleració de la gravetat mitjançant un procediment diferent a l’habitual en els laboratoris de física. També hem demostrat experimentalment que el temps de caiguda d’un cos no depèn de la seua velocitat horitzontal inicial ni de la seua massa, error molt comú entre els estudiants.