Two-photon absorption has important advantages over conventional one-photon absorption, which has led to applications in microscopy, microfabrication, three-dimensional data storage, optical power limiting, up-converted lasing, photodynamic therapy, and for the localized release of bio-active species. These applications have generated a demand for new dyes with high two-photon absorption cross-sections. This Review introduces the theory of two-photon absorption, surveys the wide range of potential applications, and highlights emerging structure-property correlations that can serve as guidelines for the development of efficient two-photon dyes.

Two-photon absorption and the design of two-photon dyes.

Spiropyrans and Spirooxazines for Memories and Switches

Cyanines during the 1990s: A Review

Linear and Nonlinear Optical Properties of Photochromic Molecules and Materials.

This report documents the library of thermodynamic data used with the NASA Glenn computer program CEA (Chemical Equilibrium with Applications). This library, containing data for over 2000 solid, liquid, and gaseous chemical species for temperatures ranging from 200 to 20,000 K, is available for use with other computer codes as well. The data are expressed as least-squares coefficients to a seven-term functional form for C((sup o)(sub p)) (T) / R with integration constants for H (sup o) (T) / RT and S(sup o) (T) / R. The NASA Glenn computer program PAC (Properties and Coefficients) was used to calculate thermodynamic functions and to generate the least-squares coefficients. PAC input was taken from a variety of sources. A complete listing of the database is given along with a summary of thermodynamic properties at 0 and 298.15 K.

NASA Glenn Coefficients for Calculating Thermodynamic Properties of Individual Species

The spectroscopic properties of solvent soluble derivatives of Brooker's simple merocyanine 4-[(1-methyl-4(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one, which can in principle exist in two distinct canonical forms, have been assessed both experimentally and theoretically using molecular orbital methods. 1H and 13C NMR evidence in a range of solvents suggests that the merocyanine exists as a resonance hybrid which is weighted toward the zwitterion even in solvents of low dielectric constants. In protic solvents, the large hypsochromic shift observed for the merocyanine in the visible region arises from both a dielectric effect and a hydrogen bonding effect. Theoretically, the PM3/COSMO method gives a reasonable account of the structure and spectroscopic shifts of the merocyanine in aprotic solvents. The large shifts observed arise because solvents with large dielectric constants have a much greater stabilizing effect on the more polar ground state of the merocyanine than they do on the first exci...

Fundamental Studies on Brooker's Merocyanine

The calculated hyperpolarisabilities of the symmetrical polyphenyls, containing an electron-donating dimethylamino group and an electron-attracting nitro group positioned at opposite ends of the conjugated system, slowly increase with an increasing number of phenyl units, but the effect per unit volume is a maximum for 4-dimethylamino-4′-nitroterphenyl. In contrast, the calculated values for polyenes containing the same donor and attractor increase rapidly with an increasing number of ethenyl units, and the effect per unit volume is a maximum for 20 units. Overall, the polyene system shows an effect which is at least 20 times that of the polyphenyl system and 10 times that of any other known system. A similar effect is also found in the dimethylaminopolyenals, though a comparison between calculated and experimental dipole moments and electronic transition energies suggests that their hyperpolarisabilities may be somewhat overestimated at the CNDO level of approximation.

Non-linear optical properties of organic molecules. Part 2. Effect of conjugation length and molecular volume on the calculated hyperpolarisabilities of polyphenyls and polyenes

Nonlinear optical properties of organic molecules. 7. Calculated hyperpolarizabilities of azulenes and sesquifulvalene

The calculated hyperpolarisabilities of substituted polythiophenes, polypyrroles and polyfurans containing an electron donor at one end of the molecule and an electron attractor at the other increase slowly with increasing number of heterocyclic rings. If the effective hyperpolarisability per unit volume is considered, the maximum values are obtained for the bifuran, the terpyrrole and the quaterthiophene. The largest hyperpolarisabilities are predicted for the polythiophenes, followed by the polypyrroles with the polyfurans showing the smallest values. Both the polythiophenes and polypyrroles have larger calculated hyperpolarisabilities than the similarly substituted polyphenyls but smaller than the corresponding polyenes.

Calculated hyperpolarisabilities of polythiophenes, polyfurans and polypyrroles

A method has been developed for the calculation of the spectra and hyperpolarisability tensor for the linear electro-optic effect at the CNDO/S level of approximation using a sum-over-states procedure with singly excited states. A wide range of dyes and pigments have been studied to assess their potential as non-linear optical materials using both static-field and frequency-dependent values. Conjugated systems containing strong donors and acceptors positioned at either end of the conjugation path show the largest intrinsic effects. Substantial resonance enhancement effects occur for molecules such as azobenzenes and azoheterocycles which absorb in the red or infrared region of the spectrum.

John O. Morley

Papers

Fundamental Studies on Brooker's Merocyanine

Non-linear optical properties of organic molecules. Part 2. Effect of conjugation length and molecular volume on the calculated hyperpolarisabilities of polyphenyls and polyenes

Nonlinear optical properties of organic molecules. 7. Calculated hyperpolarizabilities of azulenes and sesquifulvalene

Calculated hyperpolarisabilities of polythiophenes, polyfurans and polypyrroles

Calculations of the electronic spectra and hyperpolarisabilities of selected dyes and pigments