Rational Designing of Anthocyanidins-Directed Near-Infrared Two-Photon Fluorescence Probes

TL;DR

This paper designs and analyzes anthocyanidin-based near-infrared two-photon fluorescence probes with enhanced properties for high-resolution detection, focusing on structural modifications to improve emission wavelength, TPA cross section, and Stokes shift.

Contribution

The study introduces novel anthocyanidin derivatives with optimized photophysical properties for two-photon fluorescence, advancing the development of high-performance NIR probes.

Findings

2a-3 exhibits emission at 691.42 nm, TPA cross section of 957.36 GM, and Stokes shift of 110.88 nm.

Structural modifications effectively inhibit TICT, enhancing fluorescence and detection capabilities.

The work provides theoretical insights for designing advanced anthocyanin fluorescent materials.

Abstract

Recently, two-photon fluorescent probes based on anthocyanidins molecules have attracted extensive attention due to their outstanding photophysical properties. However, there are only a few two-photon excited fluorescent probes that really meet the requirements of relatively long emission wavelengths (>600 nm), large two-photon absorption (TPA) cross sections (300 GM), significant Stokes shift (>80 nm), and high fluorescence intensity. Herein, the photophysical properties of a series of anthocyanidins with the same substituents but different fluorophore skeletons were investigated in detail. Compared with b-series molecules, a-series molecules with a six-membered ring in the backbone have a slightly higher reorganization energy. This results in more energy loss upon light excitation, enabling the reaction products to detect NTR through a larger Stokes shift. More importantly, there is very little decrease in fluorescence intensity as the Stokes shift increases. These features are extremely valuable for high-resolution NTR detection. In light of this, novel 2a-n (n=1-5) compounds are designed, which are accomplished by inhibiting the twisted intramolecular charge transfer (TICT) effect through alkyl cyclization, azetidine ring and extending {\pi} conjugation. Among them, 2a-3 gains long emission spectrum ({\lambda}em=691.42 nm), noticeable TPA cross section (957.36 GM), and large Stokes shift (110.88 nm), indicating that it serves as a promising candidate for two-photon fluorescent dyes. It is hoped that this work will offer some insightful theoretical direction for the development of novel high performance anthocyanin fluorescent materials.