Linear conjugated polymer photocatalysts with various linker units for photocatalytic hydrogen evolution from water

Polymer photocatalysts have shown potential for light-driven hydrogen evolution from water. Here we studied the relative importance of the linker type in two series of conjugated polymers based on dibenzo[b,d]thiophene sulfone and dimethyl-9H-fluorene. The alkenyl-linked polymers were found to be more active photocatalysts than their alkyl and alkyne-linked counterparts. The co-polymer of dibenzo[b,d]thiophene sulfone and 1,2-diphenylethene has a hydrogen evolution rate of 3334 μmol g−1 h−1 and an external quantum efficiency of 5.6% at 420 nm

Acetylene-linked conjugated polymers for sacrificial photocatalytic hydrogen evolution from water

Conjugated organic polymers have shown potential as photocatalysts for hydrogen production by water splitting. Taking advantage of a high throughput screening workflow, two series of acetylene-linked co-polymers were prepared and studied for their potential as photocatalysts for sacrificial hydrogen production from water. It was found that a triethynylbenzene-based polymer with a dibenzo[b,d]thiophene sulfone linker (TE11) had the highest performance in terms of hydrogen evolution rate under visible illumination in the presence of a sacrificial hole-scavenger. Synthetically elaborating the triethynylbenzene linker in TE11 by changing the core and by introducing nitrogen, the resulting hydrogen evolution rate was further increased by a factor of nearly two

Theoretical Study of the Photophysics of 8-Vinylguanine, an Isomorphic Fluorescent Analogue of Guanine

Paving the way for the application of the algebraic-diagrammatic construction scheme of second-order (ADC(2)) to systems based on the guanine chromophore, we demonstrate the this excited-state electronic structure method provides a realistic description of the photochemistry of 9H-guanine, in close agreement with the benchmark provided by the CASPT2 method. We then proceed to apply the ADC(2) method to the photochemistry of 8-vinylguanine (8vG), a minimally modified analogue of guanine which, unlike the naturally occurring nucleobase, displays intense fluorescence, indicative of a much longer-lived excited electronic state. The emissive electronic state of 8vG is identified as an $\pi\pi$*-type intramolecular charge transfer (ICT) state, in which a charge of roughly −0.2 e is transferred from the guanine moiety onto the vinyl substituent. The main radiationless deactivation pathway competing with fluorescence is predicted to involve the molecule leaving the minimum on the ICT $\pi\pi$* state, and reaching a region of the $S_{1}$ adiabatic state where it resembles the $L_{a}$ $\pi\pi$* state of unmodified 9H-guanine. The topology of the $L_{a}$ $\pi\pi$* region of the $S_{1}$ state favors subsequent internal conversion at a crossing seam with the ground electronic state. The sensitivity of this process to environment polarity may explain the experimentally observed fluorescence quenching of 8vG upon incorporation in single- and double-stranded DNA

Theoretical Study of the Photophysics of 8‑Vinylguanine, an Isomorphic Fluorescent Analogue of Guanine

Paving the way for the application of the algebraic-diagrammatic construction scheme of second-order (ADC(2)) to systems based on the guanine chromophore, we demonstrate the this excited-state electronic structure method provides a realistic description of the photochemistry of 9<i>H</i>-guanine, in close agreement with the benchmark provided by the CASPT2 method. We then proceed to apply the ADC(2) method to the photochemistry of 8-vinylguanine (8vG), a minimally modified analogue of guanine which, unlike the naturally occurring nucleobase, displays intense fluorescence, indicative of a much longer-lived excited electronic state. The emissive electronic state of 8vG is identified as an <i>ππ</i>*-type intramolecular charge transfer (ICT) state, in which a charge of roughly −0.2 <i>e</i> is transferred from the guanine moiety onto the vinyl substituent. The main radiationless deactivation pathway competing with fluorescence is predicted to involve the molecule leaving the minimum on the ICT <i>ππ</i>* state, and reaching a region of the S₁ adiabatic state where it resembles the L_a <i>ππ</i>* state of unmodified 9<i>H</i>-guanine. The topology of the L_a <i>ππ</i>* region of the S₁ state favors subsequent internal conversion at a crossing seam with the ground electronic state. The sensitivity of this process to environment polarity may explain the experimentally observed fluorescence quenching of 8vG upon incorporation in single- and double-stranded DNA

Early Events in the Nonadiabatic Relaxation Dynamics of 4‑(<i>N</i>,<i>N</i>‑Dimethylamino)benzonitrile

4-(<i>N</i>,<i>N</i>-Dimethylamino)­benzonitrile (DMABN) is the archetypal system for dual fluorescence. Several past studies, both experimental and theoretical, have examined the mechanism of its relaxation in the gas phase following photoexcitation to the S₂ state, without converging to a single description. In this contribution, we report first-principles simulations of the early events involved in this process performed using the nonadiabatic trajectory surface hopping (TSH) approach in combination with the ADC(2) electronic structure method. ADC(2) is verified to reproduce the ground- and excited-state structures of DMABN in reasonably close agreement with previous theoretical benchmarks. The TSH simulations predict that internal conversion from the S₂ state to the S₁ takes place as early as 8.5 fs, on average, after the initial photoexcitation, and with no significant torsion of the dimethylamino group relative to the aromatic ring. As evidenced by supporting EOM-CCSD calculations, the population transfer from S₂ to S₁ can be attributed to the skeletal deformation modes of the aromatic ring and the stretching of the ring-dimethylamino nitrogen bond. The non- or slightly twisted locally excited structure is the predominant product of the internal conversion, and the twisted intramolecular charge transfer structure is formed through equilibration with the locally excited structure with no change of adiabatic state. These findings point toward a new interpretation of data from previous time-resolved experiments

Early Events in the Nonadiabatic Relaxation Dynamics of 4‑(N,N‑Dimethylamino)benzonitrile

4-(N,N-Dimethylamino)benzonitrile (DMABN) is the archetypal system for dual fluorescence. Several past studies, both experimental and theoretical, have examined the mechanism of its relaxation in the gas phase following photoexcitation to the S2 state, without converging to a single description. In this contribution, we report first-principles simulations of the early events involved in this process performed using the nonadiabatic trajectory surface hopping (TSH) approach in combination with the ADC(2) electronic structure method. ADC(2) is verified to reproduce the ground- and excited-state structures of DMABN in reasonably close agreement with previous theoretical benchmarks. The TSH simulations predict that internal conversion from the S2 state to the S1 takes place as early as 8.5 fs, on average, after the initial photoexcitation, and with no significant torsion of the dimethylamino group relative to the aromatic ring. As evidenced by supporting EOM-CCSD calculations, the population transfer from S2 to S1 can be attributed to the skeletal deformation modes of the aromatic ring and the stretching of the ring-dimethylamino nitrogen bond. The non- or slightly twisted locally excited structure is the predominant product of the internal conversion, and the twisted intramolecular charge transfer structure is formed through equilibration with the locally excited structure with no change of adiabatic state. These findings point toward a new interpretation of data from previous time-resolved experiments