Femtosecond Two-Photon Absorption Spectroscopy of Poly(fluorene) Derivatives Containing Benzoselenadiazole and Benzothiadiazole

Abstract

We have investigated the molecular structure and two-photon absorption (2PA) properties relationship of two push–pull poly(fluorene) derivatives containing benzoselenadiazole and benzothiadiazole units. For that, we have used the femtosecond wavelength-tunable Z-scan technique with a low repetition rate (1 kHz) and an energy per pulse on the order of nJ. Our results show that both 2PA spectra present a strong 2PA (around 600 GM (1 GM = 1 × 10−50 cm4·s·photon−1)) band at around 720 nm (transition energy 3.45 eV) ascribed to the strongly 2PA-allowed 1Ag-like → mAg-like transition, characteristic of poly(fluorene) derivatives. Another 2PA band related to the intramolecular charge transfer was also observed at around 900 nm (transition energy 2.75 eV). In both 2PA bands, we found higher 2PA cross-section values for the poly(fluorene) containing benzothiadiazole unit. This outcome was explained through the higher charge redistribution at the excited state caused by the benzothiadiazole group as compared to the benzoselenadiazole and confirmed by means of solvatochromic Stokes shift measurements. To shed more light on these results, we employed the sum-over-states approach within the two-energy level model to estimate the maximum permanent dipole moment change related to the intramolecular charge transfer transition.

Probing the Strong Near-IR Two-Photon Transition in Supramolecular Triphenylamine-based Polymers by Nonlinear Absorption Spectroscopy

“…Such an important aspect also contributes to the higher 2PA cross-section observed for polymer 3 . The 2PA cross-section values found here for all polymers associated with the LE-2PA band located in the near-IR are higher than those for other semiconductor polymers with random coil structure such as thiophene/phenylene, fluorene, phenanthrene, etc. ,− …”

“…Although it is prohibitive in centrosymmetric molecules that an optical transition is simultaneously 1PA and 2PA allowed, in noncentrosymmetric molecules like the polymers 1 – 4 , the electric dipole selection rules are relaxed . According to several works about the 2PA properties of organic molecules based on the triphenylamine-core, the lowest-energy 2PA band has an ICT character. ,− …”

“…On the other hand, the dispersion of conjugation length in random coil polymers tends to cause a structure loss in the lowest-energy 2PA band located in the near-IR region of the 2PA spectrum, which in general is related to intramolecular charge transfer (ICT) transition, as compared to the molecules and oligomers . The polydispersion generates a higher density of 2PA-allowed states, which tends to increase the magnitude of the higher-energy 2PA band (1Ag-like → m Ag-like transition) located at the visible region on the 2PA spectrum. − …”

Assessing the Donor–Acceptor Nature and the Electrochemical Stability of a Fluorene–Diketopyrrolopyrrole–Thiophene-Based Copolymer

“…Besides, coupling aromatic substitutes at the 2,7-position using Suzuki cross-coupling reactions, for instance, allows the control of its optical and electronic properties . Furthermore, applications in three-dimensional optical data storage, optical limiting, two-photon polymerization fabrication–due to a high two-photon absorption − –light-emitting electrochemical cells (LECs), as a hole transport layer in perovskite solar cells, and, recently, in optical amplifiers that can be used in visible-light communication, have been reported.…”

Sistema experimental automatizado para estudos de Laser Aleatório em plataformas poliméricas flexíveis combinadas a biomateriais

“…No campo de pesquisas cientificas o laser possui um espectro de aplicações muito grande, uma das aplicações em estudos científicos será apresentado neste trabalho de Mestrado. O laser é utilizado como ferramenta para caracterização de novos materiais, análise de biomateriais, confecção de micro dispositivos, aprisionamento de átomos [6][7][8] . Desde sua invenção em 1960 por Theodore Maiman 9 , o laser vem tendo um papel fundamental em todos os seguimentos da nossa sociedade e no desenvolvimento da mesma como um todo.…”