Strong Two-Photon Absorption in Push−Pull Phthalocyanines:  Role of Resonance Enhancement and Permanent Dipole Moment Change upon Excitation

Abstract

We study near-IR two-photon absorption (2PA) spectra of nonsymmetric push-pull metal-free phthalocyanines, which are present in solution at room temperature as a mixture of two spectrally nonequivalent tautomers T1 and T2. Large 2PA cross sections, σ 2 ) (1-3) × 10 3 GM, are obtained in the excitation wavelength region λ ex ) 815-850 nm and are explained by ( 1) a new charge transfer state appearing in the one-photon absorption (1PA) spectrum of these compounds at 420-430 nm and (2) a strong resonance enhancement within the quasi-three-level system when the Q-state(s) serve as the real intermediate state(s). In the Q-region, λ ex ) 1100-1500 nm, 2PA and 1PA transitions coincide, and the 2PA strength of any pure electronic or vibronic band is quantitatively described in terms of a two-level approximation.

Annihilation Upconversion in Cells by Embedding the Dye System in Polymeric Nanocapsules

“…The UC emission is a result of different excitation schemes: either two-photon absorption (TPA) in organic molecules, [7,8] quantum dots [1] or in proximity of metallic clusters. [9] Another well established technique is the sequential energy transfers (ETU) in rare earth ion-doped glasses.…”

New all-optical method for measuring molecular permanent dipole moment difference using two-photon absorption spectroscopy

“…So far, such measurements involving the higher-energy states, although possible, remain relatively difficult. We have found that in many practical situations a good quantitative agreement between the measured s 2 value and that calculated from perturbation theory can be achieved by considering few essential states [4,[26][27][28][29][30]. Fig.…”

“…The molecular 2PA cross-section, s 2 , may be expressed from quantum-mechanical perturbation theory as a function of transition dipole moments and permanent dipole moment differences between the states (sum-over-the-states model) [23][24][25]. We have recently shown that often in cases of practical interest good quantitative description is achieved already by accounting for two or three lower-energy states (few essential states model) [4,[26][27][28][29][30]. Here we focus on a special situation of the lowestenergy transition in dipolar chromophores.…”

Saturable absorption and two-photon absorption of 1,2,5-thiadiazolo[3,4-g]quinoxaline based derivatives with near-infrared fluorescence

“…However, there are only relatively few classes of NIR dyes that are readily available. These include the phthalocyanines, cyanine dyes and squaraine dyes [7][8][9].…”