Photolabile protecting groups (PPGs or photocages) are increasingly subject to molecular design to meet requirements such as absorbance in the visible spectral range, high molar absorption coefficients, and high quantum yields of leaving group release. Improvements in these properties for the promising 3-diethylaminobenzyl (DEAMb) photocage, the photoactivity of which is based on the Zimmerman meta effect, are reported. Expansion of the aromatic system with a second aromatic ring resulted in improved spectral properties. A systematic trend relating the electronic (π-donor or acceptor) properties of the new aryl substituent and its position in the DEAMb ring to changes in the spectral properties could be observed. Conclusions from the experimental results were supported by computations obtained by using time-dependent DFT. A second generation of DEAMb-based photocages was designed. A rigid linker was introduced to ensure more efficient conjugation of the aromatic ring π systems by limiting rotational freedom. The resulting fluorenol (9-hydroxyfluorene)-based photocages had superior spectral properties to those of simple biphenyl systems. The best uncaging cross section achieved was 5320 m cm (ϵΦ ).

Combined spectroscopic and computational studies elucidate excited-state photocleavage in DEACM cages, explaining vastly different time scales for different leaving groups.

We examine the mechanism of ultrafast internal conversion between the B band (Soret band) and the Q band in porphine (H2P), the prototypical free-base porphyrin, using electronic structure studies and on-the-fly surface-hopping nonadiabatic dynamics. Our study highlights the crucial role of dark states within the N band which are found to mediate B/Q state transfer, necessitating a treatment beyond Gouterman's classic four-orbital model. The sequential B → N → Q pathway dominates largely over the direct B → Q pathway which is found to be energetically unfavorable. Potential energy surface cuts and conical intersections between excited states are determined by TDDFT and validated by CASSCF/CASPT2 and XMCQDPT2 calculations. Both the static analysis and on-the-fly surface-hopping calculations suggest a pathway which involves minor structural deformations via in-plane vibrations. The B → N conversion is a barrierless adiabatic process occurring within ∼20 fs, while the subsequent N → Q conversion occurs via a conical intersection within ∼100 fs, in agreement with time-resolved experiments for porphine and related free base porphyrins. Furthermore, evidence for both sequential and direct transfer to the Qx and Qy states is obtained.

In view of the demand for photoactivatable probes that operate in the visible (VIS) to near infrared (NIR) region of the spectrum, we designed a bichromophoric system based on a...