Competitive radiative and reactive relaxation channels in the excited state decay of some thio-analogues of EE-distyrylbenzene

Abstract

The photophysical and photochemical properties of some thio-analogues of symmetrically substituted EE-1,4-distyrylbenzene (linear conjugation) and EE-1,3-distyrylbenzene (crossed conjugation), where thiophene rings replace the side benzene rings or the central benzene ring, have been investigated. The kinetic competition between the radiative and reactive relaxation channels of the lowest excited singlet state has been compared with that found for the corresponding hydrocarbons. The photobehaviour markedly depends on the type of conjugation and on the position (2' or 3') of the ethenic bridge with respect to the sulfur atom. The main effect of the heteroatom is an increase in the photoisomerization yield due to a decrease of the torsional barrier in S(1) and to an increase in the S(1)--> T(1) intersystem crossing, which opens the way to isomerization in the triplet manifold. Conformational equilibria, due to restricted rotation around the quasi-single bonds with the ethenic carbons, have also been investigated by selective photoexcitation for the compounds with side 3'-thienyl groups.

Banana-shaped biphotonic quadrupolar chromophores: from fluorophores to biphotonic photosensitizers

“…This is consistent with a facilitated inter-system crossing (S 1 -T 1 ). 58 Whereas compounds bearing linear alkyl chains Q1 and Q2 present a similar fluorescence anisotropy in agreement with a similar size, compound Q 0 2 lacking terminal long alkyl chains shows a smaller anisotropy ratio. Q 0 3 having similar peripheral (and central) alkyl groups to chromophore Q 0 2 reveals a lower anisotropy ratio in agreement with the smaller size of its conjugated system.…”

Bipolar and fixable probe targeting mitochondria to trace local depolarization via two-photon fluorescence lifetime imaging

“…f Radiative (K r ) and nonradiative (K nr ) decay rates. 16 nyl groups of naphthalimide. This will generate an intramolecular electric field within the fluorophore, according to de Silva et al 13 It is the photogenerated electric field that will interact with the external electric field exerted by the inner mitochondrial membrane, which affects the fluorescence lifetime.…”

Highly Emissive H-Aggregates or Aggregation-Induced Emission Quenching? The Photophysics of All-Trans para-Distyrylbenzene

“…On the other hand, intersystem crossing (k ISC ) to the triplet manifold and trans−cis photoisomerization are negligible (Φ ISC < 1%; Φ iso < 0.1%). 41,42 The low ISC rate might be associated with the relatively large energy gap between the S 1 state and the accepting state of the triplet manifold, calculated to ΔE(1 1 B u −1 3 A g ) ≈ 0.6 eV; see Figure 2. The low efficiency of photoisomerization of the all-trans isomer was ascribed to its adiabatic character, owing to substantial energy barriers in the region of 90°double bond twists, 54,56 different from the efficient diabatic process observed in stilbene.…”