Two-Photon Absorption and Two-Photon Circular Dichroism of a Hexahelicene Derivative with a Terminal Donor–Phenyl–Acceptor Motif

Abstract

Herein, we report on the theoretical-experimental analysis of the two photon absorption and circular dichroism spectra of 1-(2-pyridyl)-4-methoxy-carbo[6]helicene derivative (P6). The primary outcomes of our investigation on this particular helicene derivative with a donor-acceptor motif on one end led to two important conclusions: (1) the lengthening of the π-electron delocalization within the helical core of P6 predominantly increases the contribution of the magnetic dipole transition moment to the two-photon circular dichroism (TPCD) signal; and (2) the electric quadrupole transition moment contribution to the TPCD signal is enhanced by the intramolecular charge transfer (ICT) produced by the donor-acceptor combination on one end of the molecule. To corroborate our results, we performed a comparative theoretical analysis of the effect of the energy gap and ICT on TPCD on a series of P6-like helicenes with different donor-acceptor combinations. Two-photon absorption and TPCD spectra were obtained using the double L-scan technique over a broad spectral range (400-900 nm) using 90 fs pulses at a low repetition rate (2-50 Hz) produced by an amplified femtosecond system. The theoretical simulations were calculated using time dependent density functional theory at the CAM-B3LYP/6-311++G(d,p) level of theory.

Undecabenzo[7]superhelicene: A Helical Nanographene Ribbon as a Circularly Polarized Luminescence Emitter

“…The helicene moiety does not usually exhibit good nonlinearity, however, remarkably TPA cross-section of 1 resulted two orders of magnitude higher than that reported for carbo [6]helicene. [28] Thus, the expansion of the electronic delocalization beyond the helicene core improved the nonlinear optical responses as it has been reported for the case of hexa and heptahelicene derivatives. [29] The introduction of non-linear optics in chiral molecules, such as in the case of two-photon circular dichroism (TPCD), the non linear analogue of ECD, combines the advantages of both responses, minimizing linear absorption and scattering and giving relevant structural and conformational information of chiral frameworks.…”

Effects of External Field Wavelength and Solvation on the Photophysical Property and Optical Nonlinearity of 1,3-Thiazolium-5-Thiolates Mesoionic Compound

“…Therefore, the field of optical materials has been exploring how to develop new compounds with tunable photophysical properties or enhanced (hyper)polarizabilities for a long time. [4][5][6] So far, researchers have successfully recognized a variety of molecules with exciting optical properties, including inorganic complexes, [7][8][9] organic molecules, [10][11][12][13] metal clusters, 14,15 doped polarizable electrides, 16,17 and even macrocyclic compounds with special topology, 6,18,19 and applied some of them into practice. Among them, the conjugated organic chromophores with electron donating and electron accepting groups at both ends were one of the most popular optical units, partially due to their convenient structural tailoring.…”

Effects of external field wavelength and solvation on the photophysical property and optical nonlinearity of 1,3-thiazolium-5-thiolates mesoionic compound

“…So far, researchers have successfully recognized a variety of molecules with exciting optical properties, including inorganic complexes [7][8][9], organic chromophores [10][11][12][13], metal clusters [14,15], doped polarizable electrides [16][17][18], and even cyclic compounds with special topology [6, [19][20][21], and applied some of them into practice. Among them, the conjugated organic molecules with electron-donating and electron-accepting groups at both ends are one of the most popular optical units, partially due to their convenient structural tailoring.…”