Electronic spectra of the S1←S0 transition of dimers of protonated benzaldehyde (BZH+) with Ar and N2 are recorded by resonance-enhanced photodissociation in a tandem mass spectrometer. The S1 origins observed are shifted to higher frequency upon complexation with Ar (ΔS1 = 300 cm−1) and N2 (ΔS1 = 628 cm−1). Ab initio calculations at the CC2/aug-cc-pVDZ level suggest an assignment to H-bonded dimers of L = Ar and N2 binding to the cis isomer of O-protonated BZH+, yielding values of ΔS1 = 242 and 588 cm−1 for cis-BZH+-L(H). Electronic ππ* excitation results in a substantial increase of the proton affinity of BZH+, which in turn destabilizes the intermolecular H-bonds to the inert ligands by 35%. The drastic effects of electronic ππ* excitation on the geometric and electronic structure as well as the strength and anisotropy of the intermolecular potential (H-bonding and π-bonding) are investigated.