Benzothiazole-Based Fluorophores of Donor−π-Acceptor−π-Donor Type Displaying High Two-Photon Absorption

Abstract

A series of novel heterocycle-based dyes with donor-pi-bridge-acceptor-pi-bridge-donor (D-pi-A-pi-D) structural motif, where benzothiazole serves as an electron-withdrawing core, have been designed and synthesized via palladium-catalyzed Sonogashira and Suzuki-type cross-coupling reactions. All the target chromophores show strong one-photon and two-photon excited emission. The maximum two-photon absorption (TPA) cross sections delta(TPA) of the prepared derivatives bearing diphenylamino functionalities occur at wavelengths ranging from 760 to 800 nm and are as large as approximately 900-1100 GM. One- and two-photon absorption characteristics of the title dyes have also been investigated by using density functional theory (DFT) and the structure-property relationships are discussed. The TPA cross sections calculated by means of quadratic response time-dependent DFT using the Coulomb-attenuated CAM-B3LYP functional support the experimentally observed trends within the series, as well as higher delta(TPA) values of the title compounds compared to those of analogous fluorene or carbazole-derived dyes. In contrast, the traditional B3LYP functional was not successful in predicting the observed trend of TPA cross sections for systems with different central cores. In general, structural modification of the pi-bridge composition by replacement of ethynylene (alkyne) with E-ethenylene (alkene) linkages and/or replacement of dialkylamino electron-donating edge substituents by diarylamino ones results in an increase of delta(TPA) values. The combination of large TPA cross sections and high emission quantum yields makes the title benzothiazole-based dyes attractive for applications involving two-photon excited fluorescence (TPEF).

Excited State and Injection Dynamics of Triphenylamine Sensitizers Containing a Benzothiazole Electron-Accepting Group on TiO2 and Al2O3 Thin Films

“…Interestingly, this heterocyclic scaffold has been so far only scarcely used in organic sensitizers, 41 although it has been successfully employed in various functional materials, such as organic compounds displaying enhanced nonlinear optical properties. [42][43][44][45][46][47][48] In this paper, we present a detailed investigation of three new triphenylamine-benzothiazole sensitizers ( Figure 1) by combining steady-state spectroscopy, femtosecond time-resolved 5 fluorescence spectroscopy and femtosecond transient absorption spectroscopy in the visible and IR regions. All these techniques provide an insight into the dynamics of the excited state, the electron injection, the photo-induced radical cation generation and the formation of free electrons in the conduction band.…”

Photophysical processes of an intramolecular charge transfer fluorescent dye with carbazole units

“…In recent years, elongated molecules with symmetrical molecular architectures of D-A-p-A-D, D-A-D-A-D and D-D-A-D-D have been designed and synthesized (9,10). The application of ICT has been extended into various photochemical and biochemical processes (11,12) such as fluorescent probes and biosensors (13)(14)(15)(16), organic light-emitting diodes (OLEDs) (17,18), organic material for non-linear optical (NLO) (19,20) and two-photon absorption (TPA) (21,22).…”

Optimized Photoinitiator for Fast Two‐Photon Absorption Polymerization of Polyester‐Macromers for Tissue Engineering

“…Norrish type I and type II migration, especially occur on aromatic compounds, where relatively stable radicals can be formed. Synthesis of BA740, N,N-Bis-(2-(Acetyloxy)-Ethyl) Aniline (1) [36] The colorless solution of 54.33 g (0.299 mol) N,N-dihydroxyethylaniline, together with 120 mL (1.2 mol) acetic acid anhydride was stirred at 60 to 65 C for 2 h. After cooling, the mixture was poured into ice water and the aqueous layer was extracted with chloroform. [21] One route to avoid the self-scission and to limit diffusion, are bigger initiator molecules (macroinitiators), or cyclic ketones (cyclopentanone based PIs).…”