Significant Enhancement of Reverse Saturable Absorption Ability via Pt(II) Incorporation into the Conjugated Backbone of Benzo[1,2-b:4,5-b′]dithiophene-Based Donor–Acceptor Copolymers

Abstract

Organic nonlinear optical (NLO) materials with πconjugated electron donor (D) and/or acceptor (A) frameworks have attracted widespread attention because of their controllable performance through rationally structural tailoring, while optical limiting (OL) materials with reverse saturable absorption (RSA) ability is becoming a challenging focus in NLO research. Herein, 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (BDTT) was employed as an electron-rich building block to construct donor− acceptor (D−A)-type π-conjugated copolymers P1 and P2 and corresponding Pt(II)-incorporated copolymers P1−Pt and P2−Pt toward NLO materials. All copolymers exhibit typical RSA behavior toward a 532 nm nanosecond laser pulse. Interestingly, copolymers P1−Pt and P2−Pt show significantly superior RSA ability than P1 and P2, which is attributed to the synergistic effect of the extension of π-conjugation, enhancement of the ICT process, and especially the efficient formation of a triplet state caused by the novel Pt(II)-incorporated structure. Furthermore, copolymers show decreased band gaps with the tendency of P1 (2.48 eV) > P1−Pt (2.21 eV) > P2 (2.18 eV) > P2−Pt (1.94 eV). Correspondingly, P1−Pt and P2−Pt exhibit larger nonlinear absorption coefficients (β eff ) of 45 and 79 cm GW −1 , respectively, ca. 2.6 and 2.9 times higher than those of P1 (17 cm GW −1 ) and P2 (27 cm GW −1 ), respectively. This work presents an efficient strategy toward excellent organic NLO materials, facilitates the understanding of copolymer structure−property relationship, and promotes their advanced applications.

N-terminalized titanium carbide MXene coupled with graphene oxide toward optimized temporal domain-dependent nonlinear absorption

“…1–3 Materials with extended π-conjugation have been elaborately designed and explored to pursue remarkable NLO performance. 4–6 The successful delamination of graphene 7–9 has prompted heightened interest in numerous two-dimensional (2D) materials within the realm of nonlinear optics, which encompass graphene derivatives, transition metal sulfides, 10–16 black phosphorus (BP), 17,18 and MXene. 19–24 However, distinct drawbacks hinder the potential of individual materials: graphene's inherent zero bandgap and limited modulation depth hamper its advancement in optoelectronic devices; the large bandgap of MoS 2 along with the narrow tunable bandgap range poses challenges in future devices; the air-instability of BP and perovskites is not ideal in practical developments.…”