Estimation of the relative contributions to the electronic energy transfer rates based on Förster theory: The case of C-phycocyanin chromophores

In the present study, we provide a reformulation of the theory originally proposed by Förster which allows for simple and convenient formulas useful to estimate the relative contributions of transition dipole moments of a donor and acceptor (chemical factors), their orientation factors (intermolecular structural factors), intermolecular center-to-center distances (intermolecular structural factors), spectral overlaps of absorption and emission spectra (photophysical factors), and refractive index (material factor) to the excitation energy transfer (EET) rate constant. To benchmark their validity, we focused on the EET occurring in C-phycocyanin (C-PC) chromophores. To this aim, we resorted to quantum chemistry calculations to get optimized molecular structures of the C-PC chromophores within the density functional theory (DFT) framework. The absorption and emission spectra, as well as transition dipole moments, were computed by using the time-dependent DFT (TDDFT). Our method was applied to several types of C-PCs showing that the EET rates are determined by an interplay of their specific physical, chemical, and geometrical features. These results show that our formulas can become a useful tool for a reliable estimation of the relative contributions of the factors regulating the EET transfer rate.

Relative Order of Acidity among Hydroxyl Groups of Oxyluciferin and Emission Light Colors in Aqueous Solution

The magnitude of the acidity of the oxyluciferin in water in the ground and excited state is investigated, and it is found for the first time using computational approach that the enol group of the phenol-enol species is the most acidic in the ground state, but the deprotonation of the phenol of the phenol-keto form is the most favored in the excited state. The relative order of the acidity among the hydroxyl groups in the oxyluciferin is attributed to the sequence of the O-H bond lengths in the enol and phenol group of the phenol-enol form, and the phenol group of the phenol-keto species. The mechanism of determining the dominant emissive species in the excited state is proposed, and the dependence of emission light colors on the photoexcitation energy is elucidated by the high relative concentration of six chemical forms in the ground state and the absorption efficiency.

Preparation and optical parameter characterization of two aldehyde derivative thin films for photonic applications by drop casting method

In this study, thin films of polymer poly(methyl methacrylate) were prepared using a drop casting method. Two newly synthesized aldehyde derivatives, 2-bromomalonaldehyde and 5,6-dihydroimidazo[2,1-b]thiazole-2-carbaldehyde, were used at different concentrations to dope the films. The prepared films were transparent and therefore studied for application in photonics. Optical characterization of the samples was carried out using different spectroscopy techniques. Absorption spectra for both samples were obtained using a UV-vis light spectrophotometer. Other significant optical parameters, such as refractive index, extinction coefficient, and band gap energies, were calculated from the absorption spectra. The effect of doping concentration on these parameters was studied. Emission spectra were obtained using a fluorescence spectrophotometer and the effect of doping was observed. Fourier transform infrared spectra of the doped films were obtained and compared with the pure compound to note changes in peak values and peak intensity. This present work studied the effect of doping on optical properties and examined the application of the samples for photonics.

Influence of prototropic reactions on the absorption and fluorescence spectra of methyl p-dimethylaminobenzoate and its two ortho derivatives

The influence of prototropic reactions on the spectral characteristics of methyl p-dimethylaminobenzoate (I) and its o-methoxy (II) and o-hydroxy (III) derivatives has been studied using steady-state spectroscopic technique and quantum-chemical calculations. This study concerns the solvent-induced shift of the absorption, locally excited (LE) and intramolecular charge transfer (ICT) fluorescence bands in the neat tetrahydrofuran (THF) and its hydrochloric acid solutions at different HCl concentrations. On the basis of the experimental results and quantum-chemical calculations, it was shown that in a hydrochloric acid solution the studied molecules exist as a mixture of neutral, mono-, and dicationic forms. Additionally, the results of spectroscopic measurements were used to calculate, according to the Benesi-Hildebrand method, the equilibrium constants of protopropic reactions in the ground, S(0), and excited, S(1), states. Our findings predestine molecules I and II to be used as acid fluorescence probes in a region of 0-2.5 M of [H(+)] concentrations.