Electronic spectra and intersystem spin‐orbit coupling in 1,2‐ and 1,3‐squaraines

Abstract

The main photophysical properties of a series of recently synthetized 1,2- and 1,3-squaraines, including absorption electronic spectra, singlet-triplet energy gaps, and spin-orbit matrix elements, have been investigated by means of density functional theory (DFT) and time-dependent DFT approaches. A benchmark of three exchange-correlation functionals has been performed in six different solvent environments. The investigated 1,2 squaraines have been found to possess two excited triplet states (T1 and T2) that lie below the energy of the excited singlet one (S1). The radiationless intersystem spin crossing efficiency is thus enhanced in both the studied systems and both the transitions could contribute to the excited singlet oxygen production. Moreover, they have a singlet-triplet energy gap higher than that required to generate the cytotoxic singlet oxygen species. According to our data, these compounds could be used in photodynamic therapy applications that do not require high tissue penetration.

Molecular aspects of squaraine dyes aggregation and its influence on spectroscopic properties

“…From the computational point of view, squaraine dyes still are challenging and only scarce study is present in the literature mostly for single isolated molecules or simple models of dye-sensitized solar cell [14,[21][22][23][24][25][26][27][28][29][30]. Thus, the current contribution aims to carefully analyze mutual interactions in the small squaraine aggregates and their influence on the spectroscopic properties.…”

Photocatalytic Hydrogen Evolution Driven by [FeFe] Hydrogenase Models Tethered to Fluorene and Silafluorene Sensitizers

“…The S 1 and T 1 excited states correspond to the HOMO→LUMO one‐electron transition and in T 2 to the HOMO−1→LUMO+1. Interestingly, for both systems, the T 1 and T 2 states lie below S 1 . Not considering the effect of the different Si and C termination in 1 and 2 , we discuss the silafluorene and fluorene excitations.…”

“…Interestingly,f or both systems, the T 1 and T 2 states lie below S 1 . [47] Not considering the effect of the different Si and Ct ermination in 1 and 2,w ed iscuss the silafluorene and fluorene excitations. As expected, substitution of Si with Cl eads to the lowering in the vertical and relaxede xcitation energy of the three states considered.I n the case of 1 and 2,w eo bserve that the five-membered disulfide ring has as ignificant effect in lowering the excitation energy of 2 relative to 1.T D-DFT geometry optimization of S 1 and T 1 give the photoluminescence wavelengthsa t3 38 nm (S 1 )a nd at 611nm( T 1 )f or silafluorene,a nd at 293 nm (S 1 )a nd 558 nm (T 1 )f or fluorene.…”

Theoretical Insights into the Switching Off/On of 1O2 Photosensitization in Chemicontrolled Photodynamic Therapy

“…in which is the employed spin–orbit Hamiltonian and n = x , y , z . This protocol was successfully applied to study the photophysical properties of several dyes . The standard redox potential in solution was calculated in acetonitrile by using one of the most popular methods based on the Born–Haber cycle to derive the standard Gibbs free energy ( G ) for the reaction .…”

“…This protocol was successfully applied to study the photophysical properties of several dyes. [31,41,[66][67][68][69][70][71][72][73][74][75][76][77][78] The standard redox potential in solution was calculated in acetonitrile by using one of the most popular methods based on the Born-Haber cycle to derive the standard Gibbs free energy (G)f or the reaction. [79] The G value of the redox half-reaction, DG (sol) ,c onsists of the free energy change in the gas phase (DG (gas) )a nd the solvation free energies of the oxidized and reduced species.…”