Theoretical understanding of two-photon-induced fluorescence of isomorphic nucleoside analogs

Abstract

We use ab initio Density Functional Theory (DFT) and Time-dependent DFT (TDDFT) calculations for a detailed understanding of one-photon absorption (1PA) and two-photon absorption (2PA) cross sections of eight different nucleoside analogs. The results are compared and contrasted with the available experimental data. Our calculated results show that the low energy peaks in the absorption spectra mainly arise because of the π-π* electronic transition of the nucleoside analogs. The emission spectra of the nucleoside analogs are also calculated using TDDFT methods. The calculated absorption and emission spectra in the presence of a solvent follow the same trend as those found experimentally. Our results demonstrate that the nucleoside analogs show significantly different electronic and optical properties, although their bonding aspects towards Watson-Crick base pairing remain the same. We also derive the microscopic details of the origin of nonlinear optical properties of the nucleoside analogs.

Pulse-shaped two-photon excitation of a fluorescent base analogue approaches single-molecule sensitivity

“…21 The potential for major improvements in 2P fluorescence brightness via systematic modifications was highlighted in a study of a series of structurally-related nucleosides. 20 The 1P and 2P cross sections and spectra in that report also agree well with subsequent theoretical calculations, 22 offering the prospect of the rational design of photophysical properties. Nevertheless, until recently, FBAs have either possessed a low two-photon cross section, a low quantum yield, an absorbance maximum outside the practical range of two-photon excitation, or a combination of all three.…”

“…A number of theoretical studies of the 1P and 2P photophysics of fluorescent nucleobases have appeared recently. 22,[45][46][47][48] However, the influence of the local electric field on the 2P cross section in DNA has not been addressed. We hope that the results of the present work will stimulate theoretical studies of this effect.…”

Tautomers of a Fluorescent G Surrogate and Their Distinct Photophysics Provide Additional Information Channels

“…[12] TD-DFT excited-state geometry optimizations (employing either PBE0 or M052X) predict a stable S 1 minimum for both tautomers in all examined solvents. [13] This S 1 minimum is characterized by a fairly large oscillator strength, of about 80% of the value computed for absorption. This minimum contrasts guanosine, for which the same functionals predict a barrierless decay to S 0 , through an effective conical intersection.…”

Tuning of Hyperpolarizability, One- and Two-Photon Absorption of D-A and D-A-A Type Intramolecular Charge Transfer Based Sensors

“…The indices  and  in the above equation run over the three Cartesian coordinates and is the -th component of the two-photon tensor. The mathematical expression for can easily be derived from time-dependent perturbation theory and is given by = ∑ ⁄(11) and…”