Improving Photophysical Properties of Deazaflavin Derivatives by Acrylaldehyde Bridging: A Theoretical Investigation

The electronic structure and photophysical properties of several acrylaldehyde-bridged deazaflavin derivatives (cFLs) were investigated theoretically. The impact of acrylaldehyde bridging on photophysical properties of deazaflavin (cFL) is strongly site-dependent. Specifically, the change of adiabatic energy of electronic transitions(Delta Ead) and vibronic coupling promote fluorescent emission to be comparable to internal conversion of cFL and cFL4 (both C5-C6 and C9-N10 bridged, but C9-N10 bridged by propene), turning them eligible as fluorescent sensors. As El-Sayed's rule is satisfied in cFL1(C5-C6 bridged), cFL2(C9-N10 bridged) and cFL3(both C5-C6 and C9-N10 bridged), intersystem crossing from first singlet excited state to triplet excited states (Tn) become dominant and the evolution of excited cFLs from T1 appears vital. The rate constants of photophysical processes indicate these cFLs are of dominantly high steady state T1 concentration and are potential triplet sensitizers. We expect the findings would pave the way for rational design of novel cFLs with extraordinary photophysical properties. Acrylaldehyde bridging promotes fluorescent emission, turning cFL and cFL4 eligible as fluorescent sensors, and enhances intersystem crossing from first singlet excited state to dominate the evolution of excited cFL1, cFL2 and cFL3. High steady state concentration of T1 of cFL1, cFL2 and cFL3 suggest their potential as triplet sensitizers. image