Theoretical Studies and Design Strategies of Highly Efficient Two-Photon Excited Fluorescent Probes for Hydrogen Sulfide Detection through Simulation of Excited-State Dynamics

Hydrogen sulfide (H2S)
plays a critical role
in numerous
physiological and pathological processes, but an abnormal level of
H2S in living systems can cause various diseases. To detect
the level of endogenous H2S in a complicated biological
system, the luminous mechanism of “turn-on” probe for
H2S monitoring has been deeply explored through the simulation
of excited-state dynamic processes, and the effect of different geometric
modifications on optical properties has been minutely investigated
based on molecular modeling. TD-DFT calculations demonstrate that
line-type π-expanding in the molecular skeleton is beneficial
for improving two-photon absorption (TPA) ability, but it can give
rise to extremely large geometric relaxation, going against fluorescence
emission. It is an effective way to suppress molecular skeleton scissoring
vibration by introducing strong electron-withdrawing substituent groups
(F, Cl, Br, CN) in benzopyran, and these compounds also have superior
TPA properties in NIR. One of the potential materials in the application
of biological imaging and H2S detection has been obtained,
which simultaneously possesses easily distinguished spectra (with
a Stokes shift as large as 77 nm), high luminous efficiency (with
a quantum yield up to 20.07%), and large TPA cross section (952 GM
at 950 nm).