Benzothiazoles with Tunable Electron-Withdrawing Strength and Reverse Polarity: A Route to Triphenylamine-Based Chromophores with Enhanced Two-Photon Absorption

Abstract

A series of dipolar and octupolar triphenylamine-derived dyes containing a benzothiazole positioned in the matched or mismatched fashion have been designed and synthesized via palladium-catalyzed Sonogashira cross-coupling reactions. Linear and nonlinear optical properties of the designed molecules were tuned by an additional electron-withdrawing group (EWG) and by changing the relative positions of the donor and acceptor substituents on the heterocyclic ring. This allowed us to examine the effect of positional isomerism and extend the structure-property relationships useful in the engineering of novel heteroaromatic-based systems with enhanced two-photon absorption (TPA). The TPA cross-sections (δ(TPA)) in the target compounds dramatically increased with the branching of the triphenylamine core and with the strength of the auxiliary acceptor. In addition, a change from the commonly used polarity in push-pull benzothiazoles to a reverse one has been revealed as a particularly useful strategy (regioisomeric control) for enhancing TPA cross-sections and shifting the absorption and emission maxima to longer wavelengths. The maximum TPA cross-sections of the star-shaped three-branched triphenylamines are ∼500-2300 GM in the near-infrared region (740-810 nm); thereby the molecular weight normalized δ(TPA)/MW values of the best performing dyes within the series (2.0-2.4 GM·g(-1)·mol) are comparable to those of the most efficient TPA chromophores reported to date. The large TPA cross-sections combined with high emission quantum yields and large Stokes shifts make these compounds excellent candidates for various TPA applications, including two-photon fluorescence microscopy.

Solvent and branching effect on the two-photon absorption properties of push–pull triphenylamine derivatives

“…In both series, F F decreases upon branching, implying increased non-radiative pathways, but is maintained to relatively high values similar to those found for other TPA-based tri-podal molecules. 21,30,31 It is worth noting that F F for the tri-podal molecules remains relatively high even in solvents of high polarity such as acetone and acetonitrile ( Table 2). Fig.…”

Ultralow-threshold up-converted lasing in oligofluorenes with tailored strong nonlinear absorption

“…5,[8][9][10][11][12] Also, the nonlinear optical response in p-conjugated organic semiconductors attracts great interest in two-photon excited photoluminescence microscopy, [13][14][15] photodynamic therapy, 16 three-dimensional data storage, 17 microfabrication, 18 optical power limiting 19 and frequency up-converted lasing. [20][21][22] Previously, an enhanced two-photon absorption (2PA) cross-section has been demonstrated in structurally engineered oligomers [23][24][25][26][27] and molecules having elongated p-conjugation. 28, 29 Yet, frequency up-converted lasers, which have attracted increasing scientific and technological interest, 30 have not been demonstrated in fluorescent oligomers except dendrimers, 31 conjugated polymers, 20,21 donor-acceptor type organic molecules 22,32 and various dyes.…”

The inner-induced effects of YCN in C76 on the structures and nonlinear optical properties

“…The prediction and design of molecules with large first hyperpolarizability have received much attention, many strategies of enhancing NLO property are explored by increasing the strength of donor and acceptor, expanding the length of π conjugation, twisting π-electron systems, increasing push-pull effects, doping metal into organic compounds etc. [3,[20][21][22][23][24][25][26][27][28]; in which, endohedral fullerenes as an important strategy arouse our interest owing to π-electron-conjugated systems along with charge delocalization [29,30]. Our group has investigated the effect of different positions of Sc 2 S on the interaction energy and the nonlinear optical properties, it indicated that the change of Sc 2 S positions have significant influence on the first hyperpolarizability [31].…”